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Cooperative Extension Service

Integrated Management of Apple Pests in Massachusetts and New England

Editor

W.M. Coli, Entomology Department, University of Massachusetts

Authors

Insects and Mites

G.E. Morin, New England Fruit Consultants, Lake Pleasant, MA

R.J. Prokopy, Department of Entomology, University of Massachusetts, Amherst, MA

W.M. Coli, Department of Entomology, University of Massachusetts, Amherst, MA

Plant Pathology

C.M. Becker, Ciba Geigy Corp

D. Cooley, Department of Plant Pathology, University of Massachusetts, Amherst, MA

W.J. Manning, Department of Plant Pathology, University of Massachusetts, Amherst, MA

Orchard Understory Management

W.J. Lord, Department of Plant and Soil Science, University of Massachusetts, Amherst, MA

Vertebrate Pests

E.R. Ladd, US Department of the Interior, Hadley, MA

 

Apple Diseases

Apple Scab

Venturia inaequalis

Apple scab is the most important apple disease in Massachusetts. Modern fungicides have made apple scab epidemics uncommon, yet, in a wet temperate climate where susceptible varieties such as McIntosh are grown, scab is a disease which must be carefully managed each season. Once scab starts, it becomes increasingly difficult to limit damage, consequently it is essential to maintain early-season control in order to ensure a marketable crop of quality fruit.

Disease Cycle (Figure 73)--Apple scab overwinters in small black structures called pseudothecia. Pseudothecia develop through the winter in apple leaves which were infected the previous year (Figure 74). In the following spring, ascospores form in the pseudothecia.

Ascospores cause primary scab infections. In most seasons, ascospores mature in conjunction with apple tree development. By green tip, a few spores will be available for release. Near bloom, the maximum number of spores are mature, and by four to six weeks after bloom, all ascospores have matured and are generally released.

Ascospore release is caused primarily by moisture. Currently, it is believed that most of the mature spores are released during the first thirty minutes of a rain. However, if rains last for 2 to 3 days, additional spores mature and are released. After release, infection of green tissue requires that a film of water be present on the tissue for a given period. The length of this period depends on temperature. The relationship between leaf wetness periods, temperature and apple scab infection is known as the Mill's infection period and is described below in Management.

If primary infections develop, large numbers of secondary spores, called conidia, are produced in the lesions. High humidity and moderate temperature encourage conidial formation. Conidia can be carried throughout the orchard by water and wind, and cause numerous new, or secondary, infections. These infections produce more conidia and continue the disease cycle.

Injury-- Early in the season, scab spots or lesions first appear on the underside of apple leaves, and typically are 1/8 to 1/4" in diameter and faint olive green, slightly darker than the surrounding tissue.

Later in the season, lesions are more likely to appear on the upper surface of leaves . As lesions develop they take on a velvety olive appearance and, if severe, they may cover the entire leaf. Foliar scab is most often found in areas that are difficult to cover with spray, especially the tops of large trees or inside dense canopies. Infected leaves may remain on trees or trees may be defoliated during severe epidemics.

Fruit scab usually is caused by the secondary inoculum produced in leaf lesions. However, primary inoculum can cause calyx-end fruit infections. Lesions on developing fruit have the same general appearance as those of leaves . In early stages, the spots are somewhat smaller and darker than leaf lesions. Later, fruit spots become gray or black, and cracks develop as the characteristic "scab" forms. Late season fruit infections cause small lesions known as pinpoint scab.

Management--There are two basic techniques currently used for managing scab in Massachusetts, the protective schedule and the post-infection schedule. If primary infections start, growers may attempt eradication. In the protective schedule, fungicide is applied at seven day intervals from the time green tissue appears. If more than an inch of rain falls or leaves grow very rapidly, a second application may be made before the seven day period elapses. In the post-infection or kickback schedule, sprays are applied only after an infection period has occurred, and fungicides Which inhibit the fungus even after infection has started must be used. Usually, these fungicides are effective for 18 to 36 hours after infection starts, though newer sterol-inhibiting fungicides have longer periods of post-infection activity.

Most IPM programs employ a combination of the two techniques. No fungicides are required prior to the time ascospores begin to mature. During the early weeks of ascospore maturity, fungicides are applied on a kickback basis, or on a 7 to 10 day protective schedule. Protective sprays are used during periods of heavy ascospore release, i.e., the two to three weeks from pink to full bloom when spore release is at a maximum. At the end of ascospore release, in orchards where no scab has developed, the period between protective sprays is extended to at least 14 days. Another option is to limit applications to those times immediately before predicted rain periods. Where scab infections have started, protection must be applied at 7 to 10 day intervals for the rest of the season.

Eradicative sprays may be necessary to manage the fungus if scab lesions appear, because the secondary spores produced on these lesions can cause additional infections during the summer once the primary season has ended. The fungicides recommended for eradicative spraying reduce the number of spores produced on existing lesions and reduces the viability and germination of existing spores. Fungicides for eradicative spraying are very limited, and must be used judiciously, because resistance to these materials can develop. Consult the New England Pest Control Guide for materials and rates.

Table 1. Management Strategies for Apple Scab

Schedule Point of Chemical Action Time interval determination
Protective Between the spore and the leaf surface Approximately regular intervals, depending on weathering and time of season
Post-infection On the already germinated spore Monitoring weather data, specifically temperature and length of leaf wetness. Choose fungicides with post infection activity.
Eradication On established scab lesions As soon as established scab is discovered, repeat within 7 days if initial coverage was inadequate for complete eradication. A limited number of fungicides are available.

Ascospore maturity information can make fungicide timing more efficient. In order to detect exactly when mature spores are available in the spring, scab-infected leaves are collected the preceding fall. These leaves are placed in wire cages at sites which are representative of a given orchard. In the spring, leaf samples are removed from the cages and brought to the laboratory. Pseudothecia are microscopically examined by trained personnel in a laboratory . Maturity is rated according to the following scale.

1. Asci immature--no spores formed

2. Asci mature--no spores formed

3. Asci mature--spores formed but not colored, considered immature

4. Asci mature--spores formed and colored, considered mature 5. Asci empty--spores discharged

Mature spores may also be detected using artificial release or"spore shooting", techniques. In general, this involves stimulating pseudothecia to release ascospores in the laboratory where the spores can be collected and quantified. Both maturity data and spore release data are used to determine when mature ascospores are first available, when mature ascospores are at a maximum, and when all ascospores have been released.

When mature spores are present, it is important to monitor the length of wetting periods and the temperature during wetting periods in order to determine whether an infection his occurred. A hygro-thermograph modified to measure approximately how long leaves are wet is located in an orchard site for this purpose . This weather data is compared to the Mills' chart, which relates temperature to periods of leaf wetness to determine whether primary scab infections have started (Table 2)

The system used in Massachusetts was developed by W.E. MacHardy (University of New Hampshire). A hygrothermograph records temperature and wetting periods by replacing humidity elements with a strand of exposed, dewaxed twine. This twine extends out from the hygrothermograph, and raises or lowers a pen arm to record wetting periods. Temperature and wetting periods are simultaneously determined by the machine. The data is recorded, and growers may examine it at any point during a wetting period to determine whether infection has occurred. Using a version of Mills' chart, growers can easily determine whether a Mills' infection period has occurred.

Table 2. Apple Scab Temperature Wet Period Guide: Modified Mills' Table

Average temperature (0F) Hours of moist foliage necessary for leaf infection
78 3
77 11
76 9,5
61 to 75 9
57 to 60 10,5
55 to 56 11
52 to 54 12
51 13
50 14
48 to 49 15
47 17
46 19
45 20
44 22
43 25
42 30
30 to 41 More than 2 days

Fungicide selection is extremely important, not only in managing apple scab, but in managing all apple diseases. Factors such as retention (ability to stick to leaves) and redistribution (ability to spread in rain), and length of after infection activity vary between fungicides and are important factors to consider when the interval between sprays in increased.

Finally, it should be noted that scab-resistant apple cultivars have been developed and are being improved. Such trees remove the necessity of apple scab fungicide entirely. (More information on fungicide characteristics and on several available cultivars of disease-resistant apples is published annually in the New England Apple Pest Control Guide.)

Rust diseases are unique in that they require two hosts. While they are seldom damaging where fungicides are used to manage apple scab, changes in fungicides or spray scheduling may allow rust infections to develop.

Disease Cycle -- Both the cedar-apple and quince rust have similar, complex life cycles (Figure 79). Two years are necessary for the fungus to complete the disease cycle, and both apples and junipers are involved in the cycle. In spring, galls expand and produce gelatinous spore horns. On twigs of eastern red cedar and occasionally other junipers. the cedar-apple rust fungus produces brick-red to chocolate brown galls that may vary in size from Us to 2 inches in diameter . The galls produce spectacular gelatinous, bright orange spore horns during spring rains from late April through early June . Galls of the quince rust fungus occur as spindle-shaped enlargements on stems of numerous varieties of juniper. During damp weather in early spring, normally inconspicuous galls enlarge and produce an orange-brown gelatinous mass, similar to the spore horns on cedar-apple galls. These horns release spores (basidiospores) within 30 minutes after the start of rain. Spores are released for the duration of the wetting period or as long as the relative humidity is greater than 85%. Once basidiospores are released, infection occurs after wetting periods only 1/2 to 1/3 as long as those required for apple scab infections. Fruit are most susceptible to infections from the tight cluster through petal fall stages of tree development.

Rust lesions develop in one to three weeks, appearing as small orange spots on the upper surface of leaves. During late July and August, lesions on the lower leaf surface release spores (aeciospores). Wind disseminates the aeciospores to junipers. New galls develop on the junipers. These galls require a minimum of 19 months to mature and will produce spores which infect apple. Cedar apple rust galls in eastern red cedars are active for only 1 season, while quince rust galls on the low spreading junipers and red cedars are active for many years.

Injury -- Cedar-apple rust causes brightly colored spots , and to a limited extent. fruit spots. Leaf spots begin to appear shortly after bloom. Small, pale yellow spots first develop on the upper leaf surface, gradually enlarge and develop orange centers with orange-colored margins. When spots are about 1/8 inch in diameter, they exude an orangish liquid. Within several weeks, black dots appear on the upper surface of the spot. Late in the summer lesion development becomes evident on the lower leaf surface, as small cylindrical tubes protrude within the lesions, giving them a convex shape.

Severe infections cause defoliation, stress the tree, and make some fruit unmarketable. The varieties Golden Delicious, Rome, and Jonathan are most susceptible to cedar-apple rust.

Fruit infections from cedar-apple rust occur infrequently and are often located near the calyx. Fruit infections differ from leaf infections in that they have a dark green border and seldom have fruiting bodies. Fruit may become misshapen.

Quince rust causes fruit infections, but rarely leaf infections. Fruit infections are typically found on the calyx end of a young fruit. Initially the diseased area is depressed and the skin is dark green. As fruit enlarges, the infected area remains constricted. and fruit become malformed ). Tissue below the lesion dies and appears brown and spongy. This differentiates quince rust fruit infections from those of cedar-apple rust, where tissue remains alive but corky beneath lesions. In Massachusetts, quince rust is more common on Delicious than on any other variety.

Management -- To some extent rust diseases may be reduced by removing junipers and red cedars surrounding the orchard. To completely eradicate the disease, however, all alternate hosts must be painstakingly removed for a distance of two miles surrounding an orchard. Therefore, if an orchard has a history of rust, fungicides with activity against rusts should be included in the spray program. Since most basidiospores are released from galls from early pink to full bloom, focus rust fungicide applications at this time. Rust control cannot be achieved with post-infection applications, as most presently registered fungicides have no kickback against rusts. (Triforine is a recently registered fungicide which does have some post-infection activity against rust.) Hence, most fungicides must be applied as protectants prior to rain.

Black Rot

Physalospora obtusa

The black rot fungus causes a fruit rot, and a leaf spot (frog-eye leaf spot). It is also the most common cause of cankers on apple trees in Massachusetts. Black rot has a very wide-range of wild hosts, hence inoculum is usually abundant.

Disease Cycle (Figure 84) -- The black rot fungus overwinters in cankers, in old prunings, in mummied fruit, and on many wild hosts. Spores are produced in pycnidia and pseudothecia on diseased tissue. Spring rains discharge spores and carry them to susceptible tissue. Although the fungus can infect leaves directly, it is a weak pathogen and normally requires open wounds, dead tissue or stress to cause fruit or wood infections. The heaviest discharge of spores occurs around bloom, but spores are released throughout the summer. Once released, spores may germinate within 5 or 6 hours at warm temperatures while at lower temperatures germination times are longer. Spores can remain viable for up to six years, as long as bark covers the sporeproducing tissue.

Injury--The fruit rot caused by the black rot fungus is characterized by concentric rings of brown to black on infected areas of the fruit . Rotted areas remain firm, with a leathery texture. Severely infected fruit, shrivels up, dries and remains on the tree as a black mummy particularly on cultivars such as Cortland. Black rot mummies also occur when chemically thinned fruit fails to abscise and becomes infected with the fungus.

The leaf spot stage of the disease begins as circular brown spots, called frog-eye leaf spots ). Leaf spots often extend to larger irregular lesions with a purple margin, as a response to secondary fungi or certain pesticides (especially those lacking manganese). Severe foliar infections may result in substantial defoliation and premature fruit drop.

Black rot cankers are found on branches weakened by stress. Injuries and pruning cuts serve as the major sites of infection . Infections may spread in the wood, and kill significant portions of a tree. Very young trees can be killed by black rot which started in small injuries.

Management -- Black rot is managed using a combination of sanitation, good horticulture, and fungicide applications. Removing dead and infected branches and mummies reduces potential inoculum. Also, removing and burning all prunings before spring removes a site where black rot inoculum can develop. Vigorously growing trees are less subject to cankers, so good horticultural practices reduce tree damage. Dormant pruning rather than spring or summer pruning reduces chances of the black rot fungus invading pruning cuts. Remove black rot cankers well below the canker margin. Fungicide applications are necessary to properly manage fruit and leaf infections from pre-pink through harvest.

Minor Canker and Fruit Rot Diseases

Cytospora, Phomopsis, Phoma, Gloeosporium, Botryosphaeria

A number of fungi cause apple diseases which appear to be similar to black rot. Because relatively little is known about the biology of these pathogens, and the diseases they produce occur infrequently, they can be discussed as a group. Bitter rot, a fruit rot discussed below, is also related to some of these diseases.

Disease Cycle--Generally, the disease cycles of these fungi seem very similar to that of Physallospora. Mummified fruit, infected wood and wild hosts provide reservoirs of inoculum. Splashing rain in warm weather spreads spores, which infect fruit and/or wood. Stress and wounds predispose wood to infection.

Injury-- Cytospora infects wood, and is one of the most frequently found saprophytes on wood which has been killed by freezing, drought or other problems. During summer, numerous fruiting bodies (pycnidia) appear as pimples on the bark of infected wood . Spores are exuded as long amber-colored tendrils during wet periods. Wounds or pruning cuts appear to play an important role in initial infections, but, once established, the fungus can cause cankers. Bark in a canker may be depressed and off-color before pycnidia erupt.

Phomopsis causes canker or rough bark disease, mostly on the smaller branches of old neglected trees. Bark in the cankers is cracked into small sections with ragged edges. In spring, fruiting bodies (pycnidia) produce spores which ooze out in cream colored tendrils. These spores infect wounds in bark. Some cankers spread to infect or girdle whole branches. Phomopsis mall causes an apple core rot.

Phoma cankers are similar to Phomopsis cankers. Brooks fruit spot, or Phoma spot, is actually caused by the fungus Mycosphaerella pomi. The etiology of Phoma on apples is poorly understood.

Gloeosporium is an anthracnose fungus which causes some twig dieback, especially on Delicious and McIntosh. It produces small superficial lesions on the bark of young twigs. Cankers may be either scattered or very numerous on a limb. The cankers begin to develop in late fall when they appear as small circular reddish spots. In spring, cankers enlarge and reach full size by May. Conidia are produced in fall one year after infection occurs, while ascospores from the perfect stage (Neofabraea) are released in the fall of the second year. Fruit may be infected.

Botryosphaeria dothidea causes a canker and fruit rot, and is commonly called Bot rot or white rot. It is rare in Massachusetts. On twigs the disease causes small circular spots which exude a watery liquid. The next spring, bumps appear on the canker surface, indicating formation of fruiting bodies (pycnidia). Bark sloughs off, revealing a shiny tissue and the pycnidia. Large branches may be affected. On fruit, lesions appear as reddish spots. Infected tissue is mushy, and turns from a bleached appearance to brown. Golden Delicious are especially susceptible to the fruit rot. Fruit and branch infections appear throughout the summer.

Management -- As with black rot, a combination of sanitation, good horticulture and a spray program will keep orchards relatively free of these diseases. Pruning diseased branches should always be done 6 to 12 inches below the infection. Where fruit rots occur, summer fungicides should be applied on a more frequent basis than in those orchards where rots are absent and primary scab has been controlled.

Bitter Rot

Glomerella cingulata

Bitter rot is usually a late season disease of apple fruit. Where fungicides are applied regularly, the disease is rarely a problem. Occasionally heavy losses from bitter rot occur when warm summer temperatures, prolonged rain, and abundant inoculum combine to favor disease development.

Disease Cycle -- The bitter rot fungus overwinters as a saprophyte in many wild trees surrounding orchards, and in mummified fruit within the orchards. The latter is considered the most important inoculum source, although dead or dying apple limbs also release spores. Spores from these sources are produced in abundance during periods of warm ( > 20C) and moist (rainy or very humid) weather, and are normally ready for release by June. Rain induces release, although a few spores may be released without rainy weather. Maximum release occurs in evenings and early mornings, especially during rain. Spores are disseminated by wind and germinate as soon as 5 hours after they land on the surface of an apple. Bitter rot spores are capable of infecting uninjured fruit by direct penetration. Hence, disease incidence increases rapidly throughout an orchard when conditions favorable for infection occurs. Other crops such as grapes and pears can be infected by the fungus and serve as inoculum sources.

 

Injury--Although bitter rot may appear on apples when the fruit is half grown, it is more common for symptoms to develop as the fruit approach maturity. Onset of infection may start as early as July. The rot is first apparent as small, brown, circular spots. Lesions expand rapidly, forming saucer shaped depressions in the flesh of the apple. The fungus develops orange spore producing structures, called acervuli. The acervuli form in concentric rings in the lesion (Figure 89). In humid conditions, acervuli produce a creamy mass of salmon-pink spores (conidia). One to many lesions may develop on a single fruit.

Management--Bitter rot is managed through a combination of sanitation and the application of fungicides. Mummified fruit and declining twigs may harbor the bitter rot fungus. Removing mummies and dead and dying wood reduces sources of bitter rot inoculum.

Fungicide applications are necessary to properly manage fruit infection during warm and moist summers. Summer cover sprays applied to control black rot, sooty blotch and flyspeck, should effectively reduce bitter rot infections when used at 3-4 week intervals. Early infections may occur during warm, moist springs. Not all apple scab fungicides control bitter rot. In orchards with a history of bitter rot, the scab fungicides selected should also have activity against the bitter rot fungus.

Calyx End Rot

Sclerotinia sclerotiorum, Botrytis cinerea,

and Alternaria

Calyx end rot of apple is an occasional problem in Massachusetts. It is observed sporadically on immature McIntosh, Red Rome and many early varieties. Infections of up to 30% may occur in some orchards

Disease Cycle -- Several common fungi such as Botrytis and Alternaria can cause end rots, but the most serious problems are caused by one species. Sclerotinia sclerotiorum. This fungus is believed to overwinter as sclerotic in fallen fruit or orchard duff. The sclerotic produce apothecia. which probably release spores from late pink to petal fall. These spores apparently infect susceptible developing fruit at this time. Lesions appear on the developing fruit as the fungus grows. After the fruit drops, the fungus produces sclerotic. Some end rot fungi invade fruit before the calyx closes. These infections may develop into moldy core, either on the tree or in storage.

Injury--Calyx end rot is first observed soon after bloom when fruit are 3/3-3/4" in diameter. Light to dark brown lesions expand from the calyx. The affected tissue is initially soft. but it eventually dessicates leaving a leathery surface with a corky layer beneath (Figure 90). In advanced stages of infection the center of the lesion surface is grayish tan and is surrounded by a black or reddish border. Usually. infected fruits drop by mid-August.

Management -- The traditional apple scab fungicide program may not be sufficient for adequate control of calyx end rot. Since little is known about the end rot disease, good management strategies for them do not yet exist. It may be undesirable to store apples for a long period if they come from an area where end rot infection levels are high. Such fruit often develops rot problems.

Powdery Mildew

Podosphaera leucotricha

Powdery mildew can reduce vigor and productivity of apple trees by disfiguring leaves and killing newly emerging twigs and blossoms. While the disease is not of major concern in Massachusetts, powdery mildew seems to be increasing where mildewcides (especially sulfur or benomyl) have been absent from spray programs for several years. The varieties Cortland, Rome, Jonathan, Paulared, Idared and Baldwin are most susceptible to powdery mildew.

Disease Cycle-- The powdery mildew fungus overwinters as fungal mycelium in vegetative and fruit buds. As buds break dormancy, the fungus starts to grow and colonizes developing leaves, shoots and blossoms. Infections occur when the relative humidity is greater than 90% and the temperature is between 50 and 77F. No leaf wetting is necessary for the development of the fungus. Late season infections on leaves and vegetative shoots enable the fungus to enter newly formed buds, where it may cause increased damage the following year.

Injury--Powdery mildew infections are first visible on young, expanding leaves. Leaves appear to be covered with a white powder and are often curled and distorted (Figure 91). Infected blossoms open later than disease-free blossoms. are distorted, and rarely set fruit. Severe infections result in a web-like russetting on the mature fruit (particularly Jonathan). Newly emerging shoots and young fruiting spurs may be covered with white-gray mycelium and small black fruiting structures of the fungus called cleistothecia (Figure 92). Cleistothecia are usually observed late in the growing season.

Management -- Powdery mildew inoculum may be reduced by pruning infected terminals. However, this may produce poor tree structure, so fungicides are usually the preferred management tool. Several low dosage sprays of an appropriate fungicide at seven day intervals from tight cluster to petal fall are essential for management of powdery mildew. After petal fall, cover sprays should also be applied until terminal growth stops on highly susceptible varieties. These practices are necessary only where the disease has been identified as a problem.

Sooty Blotch and Fly Speck

Gloedes pomigena

and Zygophiala jamaicensis

Sooty blotch and fly speck are fungal diseases often found together on apple fruit in late summer. They are usually considered together as the "summer diseases". While both diseases are only superficial and cause no actual damage to the fruit, their presence on the fruit surface lowers marketability.

Disease Cycle--The sooty blotch fungus overwinters on infected young twigs of numerous wild tree species. Spores (conidia) are released from infected twigs during cool, rainy weather, particularly in May and June, and in early fall. Infections which cause problems are most likely initiated on young fruit (1/4 to 1/2") or on nearly mature fruit after the last spray application. Temperatures around 65F are most favorable for growth of the fungus with practically no growth occurring at 85F. A combination of cool, rainy spring weather, with late summer rains, and periods of low temperature in early fall are most favorable for severe outbreaks of sooty blotch and fly speck.

Injury -- Sooty blotch appears as dull black to gray spots, 3/8-3/4 inch in diameter . The black, powdery fungus is superficial and can be removed by vigorous rubbing. Fly speck forms as distinct black superficial specks in groups of about 10 to 40 . Several groups may be scattered over the surface of a single apple.

Management--Both diseases are easily managed with fungicides. The diseases require at least 30 days from infection until the blotches and specks become visible, so preventative applications of spring and summer fungicides with a spectrum of activity against sooty blotch and fly speck should be utilized. Generally, fungicide programs for other diseases will control these diseases.

Since infections are most likely on lower branches where dews are likely to linger, mowing grass and weeds will improve air circulation and reduce the potential for disease development. The disease may cause severe problems during cool, wet harvest seasons on late varieties. During such seasons late varieties may require an early September fungicide spray.

Fire Blight

Erwinia amylovera

The fire blight bacterium, while not a major apple disease in Massachusetts, can cause serious losses of blossoms and fruit, and destruction of twigs, branches, and fruit spurs. The disease is most serious on the varieties Rome, Jonathan, Idared, and Mutsu. All commercially grown pear varieties are highly susceptible to fire blight.

Disease Cycle -- The bacteria overwinter in bark infections on the host. During spring, cankers may produce an ooze containing millions of bacteria capable of spreading infections. Insects and rain are the major vectors which spread the bacteria. Pruning instruments will also spread the organism.

The disease becomes a concern when weather is warm and moist, and the bloom period is prolonged. Several days during bloom with temperatures from 65 to 85F with relative humidity greater than 60% will greatly increase the chance of the blossom blight phase of the disease. Once the blossoms are severely infected, bacteria can easily spread to fruiting spurs. Infections then spread to adjacent leaves and terminals. This is the twig blight stage of the disease, and indicates that the pathogen is well established and may cause long-term destruction.

Injury--Early season infections first appear during bloom. Blossoms rapidly wilt, appear water soaked and have a dark green color. The entire fruiting spur may become invaded within a few days. Infected tissue turns brown to black as if burned, which gives the disease its name. Leaves often become infected through the petiole, causing the midvein to be the first leaf tissue to become discolored, followed by a darkening of the lateral veins and surrounding tissue. Blighted twigs wilt from the tip and express a characteristic crook .

Branch or trunk infections range from large, depressed, water-soaked cankers to inconspicuous spots. Either type of branch infection may produce ooze as the bacterium begins growth in the spring.

Management--To manage the disease several factors should be considered:

1. Fire blight occurs sporadically in New England. If the disease hasn't occurred in an area, then there is no point in using chemicals to manage the disease. It is important to detect new infections as early as possible, since early treatment is most effective. When there is a history of fire blight in an orchard, a spray program should probably be used.

2. Fire blight bacteria grow best when the temperature is warm (65 OF or more) and the humidity is quite high. Rainy, warm weather encourages fire blight. In areas where the fire blight has occurred in the previous season, warm, rainy weather in the spring will probably initiate an outbreak of the disease.

3. The bacteria need an opening to enter a tree. These openings may be natural, such as flowers or leaf lenticels, or mechanical injury such as is caused by hail or pruning.

4. Once in the tree, the bacteria must generally be physically removed to eliminate the infection. This means pruning damaged areas, making cuts at the healthy wood well below the visible symptoms. Tools should be sterilized between cuts with either bleach in water, 1: 9, or alcohol at 30-75% .

Bactericidal chemical sprays cannot cure established infections, but can slow disease spread. The first spray, at silver-tip to green-tip, is a Bordeaux mix plus oil, and is designed to reduce the number of Overwintering bacteria. At bloom, when temperatures above 65F and relative humidity above 60~b for 24 furs. are expected, sprays should be applied. A Bordeaux mix (2-6-100) spray should be applied when temperature is at least 70F, and drying is relatively good. (Note: Bordeaux mix can be phytotoxic.) The first spray should be applied any time after the first blossoms open. If weather favorable for infection continues, or is predicted, a second spray should be applied around 50% bloom. A third spray may be applied at the end of bloom. Bordeaux may cause fruit russetting, and it's use should be limited to dilute applications during dry weather. (See Peach, Pear and Plum Pest Control Guide for Southern New England for more specific recommendations.)Streptomycin is an antibiotic which has been successful in controlling fire blight epidemics. It is a valuable tool in managing severe outbreaks of the disease. It should not be used as a routine chemical control, since bacteria can rapidly become resistant to it. If a grower believes fire blight in his orchard warrants streptomycin, he should contact the plant pathologist responsible for tree fruits in his area.

Blister Spot

Pseudomonas syringae pv. papulans

Blister spot is a highly specific disease, essentially effecting only one cultivar, Mutsu. As Mutsu acreage increases, the disease becomes more important. However, other varieties are not immune and can develop blister spots.

Disease Cycle -- The Overwintering and dissemination of blister spot bacteria is not well understood. Bacteria may overwinter in bark cracks or buds as in other Pseudomonas diseases. Fruit are apparently most susceptible during a period approximately 2 weeks after petal fall. Bacteria enter stomates on the fruit, and develop large populations. This build-up is favored by warm, humid weather.

Injury -- The bacteria infect fruit lenticels, and cause reddish brown spots approximately /6 to l/4 inch in diameter. These spots are sunken slightly in the fruit surface (Figure 96). The infection does not progress deeply into the fruit, but does significantly reduce marketability. A leaf spot occurs rarely.

Management--Mutsu growers should assume blister spot will occur if the disease was previously present in the orchard, and if weather is warm and humid 7 to 10 days after petal fall. In tests, the antibiotic streptomycin has been successfully applied during the 2 weeks following bloom. However, no materials are presently registered to control blister spot.

Nectria Twig Blight

Nectria cinnabarina

Nectria twig blight is of importance on only a few varieties which have large cluster-bud bases, such as Rome and Northern Spy. The disease may look like fire blight, but requires different controls.

Disease Cycle--Heavy infections often follow a season with a late harvest, indicating that infections occur in late fall. Viable spores exist from September through the winter. Spores are carried in rain water. In June, leaves on infected twigs wilt and die. Blighted blossom clusters are not retained, and the blight doesn't appear to progress from the tip. Cankers develop at the base of diseased twigs, later in the summer, bright pink or red fruiting structures appear on the canker surface.

Injury -- Injury is usually limited to the cluster bud base and adjoining twig. Though the disease is seldom severe, Nectria may sometimes invade wounds on larger branches and girdle them .

Management -- Chemical controls specifically for Nectria have not been developed because detailed knowledge on the pathogen biology does not exist. Removing infected twigs has no major effect on later infections, and it is nearly impossible to find and prune all infections.

Root Diseases

Phytopthora, Nematodes and Apple

Replant Disease

A number of micro-organisms can cause root problems on apple trees. Apple roots may also be stressed by abiotic factors, such as winter freezing, excess water, drought, or poor soil structure. When diagnosing a problem, it is often difficult to tell which factor is most important. In general, most root problems produce similar symptoms on the above

ground tree. Trees with damaged roots often have leaves which suddenly shrivel and die as if affected by drought. Leaf scorching usually indicates poor water transport which often indicates a root problem. Root problems are more severe on young trees because small trees cannot tolerate much root damage. Whereas an old tree may not produce well because of root problems, an affected young tree often dies.

In some instances, trees show a low, uneven growth pattern. When trees develop such problems after being planted on an old orchard site, it is often referred to as apple replant disease. The exact causes of apple replant disease remain unknown, though various microorganisms have been implicated in different manifestations of the problem. Alternatively, preplan" root dips with systematic nematicides or post-plant nematicide applications may reduce high nematode populations. Treating only the planting holes with an insecticide nematicide is another possibility.

Nematodes are one of the many factors contributing to apple re-plant disease. Nematodes are microscopic worms which live in the soil along with bacteria and fungi and feed on root tips. The feeding process injures or kills root tips and leads to problems of water and nutrient absorption. The resulting wounds usually become infected by root rotting fungi. In addition, some nematodes can transmit virus diseases.

A vigorously growing, mature tree can support a large number of nematodes without showing any symptoms. However, trees coming from the nursery. especially those in poor condition or being planted under adverse conditions, cannot tolerate this damage. Experiments at Cornell University and elsewhere have shown that the head start given to small trees by soil treatment is never lost even when high nematode populations return after a year or two.

Soil samples from Massachusetts orchards always contain plant-parasitic nematodes, usually of several different species. The three most common, and most injurious, are the lesion, dagger and ring nematodes. Lesion nematodes, Pratylenchus spp., migrate through the inner root tissues. breaking them down as they feed. Dagger nematodes, Xiphenema americanum, have spears which penetrate into the root tip and cause it to swell and stop growing. Dagger nematodes can transmit the virus that causes peach stem pitting or apple brown line and theoretically only one infective nematode is necessary. Ring nematodes, Criconemoides and Macroposthonia, are root surface feeders. Injury is not severe, but helps to slow down the growth of young trees.

Before planting, sites should be sampled for nematodes. Because nematodes are distributed in clusters throughout the field, it is important to collect soil from several areas. For each 5000 sq. ft. area, 10 or more subsamples taken to a depth of 8-10" from the strip where trees are to be planted should be collected with a trowel or spade. Mix the soil in a bucket and then put one quart of mixed soil in a plastic container. If a sampling tube is used, about one quart of soil should be collected. Samples should not be allowed to dry. Soil samples may be taken at any time during the year although winter and spring populations will be low and less representative of the peak population. Samples should be analyzed by a nematologist.

If a grower decides to treat soil, fumigation which reduces all disease organisms is probably the most effective procedure. Land should be prepared by removing old roots, and developing the top soil so it is friable and free of clods. This may mean cover cropping for a year. Finally, fumigation should be done by a trained applicator.

Phytophthora, Collar rot and crown rot are serious root diseases which occur in Massachusetts. The diseases are caused by the same fungus, Phytophthora, and differ only in the initial point of infection. Infections occur from the soil line to the crown area where major roots emerge from the tree. The diseases can girdle the trunk, and move along both trunk and primary roots. A distinct margin between healthy and necrotic tissues is usually present. The diseases are frequently associated with soil moisture extremes and temperature stress. However, the environmental conditions, and even the fungus species, which cause the disease are not well understood. One rootstock, MM106, is particularly susceptible. Presently, a fungicide for controlling collar rot is in the process of being released. This fungicide is applied as a soil drench on problematic sites.

For more information on Rootstock/Site/Disease Interactions.

Integrated Orchard Floor Management Systems

Integrated orchard floor management systems (IOFMS) are part of integrated pest management (IPM) strategies. Neither IPM or IOFMS replace selective, safe and efficient chemicals in crop and weed management but encourage the judicious use of chemicals along with other economical nonchemical methods and strategies.

It can be argued that IOFMS is simply new terminology for systems that were called soil management or orchard floor management. Nevertheless IOFMS is a much more important factor in IPM strategies than most orchardists realize since insects, diseases, rodents, water, nutrients and herbicide persistence can be affected by rootstock/insect/disease interactions, the type and position of the ground cover, and/or the absence of a ground cover. IOFMS should start before the trees are planted and the systems used in New England are sod, mulch, cultivation, herbicides, and various combinations of these.

Pre-Plant Treatments

Hay fields and pastures. Frequently, hay fields and pastures are planted to fruit trees without soil preparation. Since most growers do not irrigate or heavily mulch trees, the lack of soil preparation often is the cause of poor growth the year of planting. Whenever possible, it is desirable to plant fruit trees in tilled strips, regardless of the soil management followed later. An alternative to the tilled strips particularly where the soil is stony are herbicide strips Paraquat (trade name) or Roundup' can be applied in late summer in 4-6 foot wide strips where the trees are to be planted. The herbicide can be applied again in late fall or the strips rototilled. If the strips are rototilled they can be "worked-up" again prior to planting in the spring.

Newly cleared land. On newly cleared land and soils which are low in fertility and are not too stony or likely to erode badly, it is advisable to build up the soil by seeding and plowing or dishing under cover crops before planting trees. Spring oats, buckwheat, or millet can be sown as the summer cover crop and spring oats for the winter cover crop. This is an opportune time to apply lime because it can be incorporated into the soil during the dishing of the cover crops. Perennial weeds such as brambles, sumac, sprouts of hardwood trees, or poison ivy may be on newly cleared land and should be treated with an herbicide the season before planting.

Old orchard site. When an old orchard site is renovated nematode populations should be determined because some nematodes transmit viruses while others may reduce tree growth by feeding on young roots.

Rootstock/Insect/Disease Interactions

Size-controlling rootstocks, in general, are more demanding than seedling rootstocks in respect to drainage, depth of soil, and water holding capacity. Thus, the proper match between rootstock and soil may be the difference between the success or failure of the planting.

All the common clonal rootstocks except M13 are sensitive to "wet feet"; M26 and MM106 appear to be the most sensitive. A pan within 20 inches of the soil surface may impede drainage early in the growing season and cause mortality of trees on clonal rootstocks including MM 111. MM 111 reportedly is tolerant both to dry and wet soils. Trees on M26 planted on shallow (less than 20 inches) soil over bedrock, may show water stress in droughty summers, especially on the sandier soils.

For M26 and M9 good deep soils, average to good drainage and good waterholding capacity appear needed. These soils include Colrain fine sandy loams, Charlton fine sandy loam and Brookfield fine sandy loam. MM106 also should do well on these soils and on soils classified as light, gravelly or sandy soils without the tendency to drought. This group of soils, among others, includes Canton fine sandy loam. M7A should do well on the same soils as M9 and MM106 plus soils that are good except with hardpans below 24 inches. (A more complete discussion of matching rootstocks and soil can be found in "Establishment and Management of Compact Apple Trees". Cooperative Extension Service, University of Massachusetts C102.)

Rootstocks vary in winter hardiness and influence tree survival. Winter hardiness of a rootstock relative to others may also differ in early, mid, or late winter. M9, M7A, or M26 will induce early maturity of the scion, therefore they tend to protect trees from damage from fail or early-winter freezes. In contrast, the tendency of trees on MM106 to grow late in the season appears to increase susceptibility to early winter freezes, collar rot, and fire blight. K- 14, the Bud. series, Hibernal and Robusta 5 stocks are all very tolerant to low mid-winter temperature. Nevertheless, Robusta 5 is low temperature sensitive in late winter and early spring because of very low chilling requirements (a short dormancy).

In New England, MM 106 is recommended for planting on only lighter soils because of its extreme susceptibility to collar rot on wet soils. Fire blight susceptibility varies with rootstocks. M9 and M26 rootstocks are highly susceptible, MM106 is moderately so, while M7A and MM111 are relatively resistant. M9, M26 and M7A are highly susceptible to woolly apple aphids, normally a secondary problem in New England but with the potential of becoming a major pest under certain spray programs. M9 stem-pieces on interstem trees are the site for fire blight entrance probably because of the presence of burrknots. (Rootsuckers are also fire blight entry sites.) Such burrknots are also feeding sites for apple bark borer. Deeper planting will reduce root suckering and reduce number of burrknots exposed to insect and disease problems. Placement of sand or gravel around the tree base helps to keep the area dry and reduces the danger of collar rot.

Sod

Generally, newly set fruit trees, and probably trees on rootstocks of M26 vigor or less, do very poorly in a heavy grass sod because of competition with the sod for moisture and nutrients. This objection to sod can be resolved by installation of trickle irrigation.

A vigorous orchard sod requires mowing 3-5 times per season. Mowing is expensive and requires considerable energy but does aid in mouse control by depriving them of cover. Fortunately, growers now can mow closer to the tree trunks, and reduce the need of herbicides, by purchasing a swing-arm mower. However, particular care is needed when operating a swing-arm mower to prevent tree damage in young plantings and/or when trees lean.

The most common grass species used as orchard cover are Kentucky bluegrass, smooth bromegrass and orchard grass. However, creeping red fescue may be a better choice because it requires less mowing and will suppress the influx of broadleaf weeds such as milkweed, clover and goldenrod which attract foraging bees and may preclude the use of Penncap-M (trade name) against crawlers of San Jose Scale. Red fescue is reported to be quite slippery particularly when wet, although conversation with local growers do not indicate that this has been a problem under New England conditions. To the contrary, it has been claimed that the heavily matted nature of a fescue cover provides a more firm operating surface, particularly in wet years. Leguminous plants like alfalfa and common vetch are alternate hosts for tarnished plant bug. Weeds may also serve as a reservoir of Tomato Ring spot virus (TmRSV) which is associated with a disease known as apple union necrosis and decline. Apple trees in orchards become infected with TmRSV through inoculation by dagger nematodes which acquire this virus from previous trees, from current weed cover, or infected nursery stock.

Cultivation

Cultivation generally is practiced only in young plantings when land has been cleared from woods or when an old orchard site is renovated. After a year or 2, grasses and weeds are allowed to reestablish themselves between the rows or the land is re-seeded.

In the cultivated orchard the whole area between the trees is cultivated during the late spring and early summer. Then grasses and weeds are allowed to reestablish themselves in early July or a cover crop of rye is planted to prevent late growth of trees and/or soil erosion the following year. The cover crop is allowed to grow in the spring until growth of the trees is well started. It is then dished and the land again kept free of weeds by cultivation until early July. A modification of the system is sometimes adopted on moderately steep slopes. Narrow strips on either side of the tree row are cultivated and the row middles are kept in permanent sod. After the trees have become well established the cultivated strips may be seeded to a grass mixture, creeping red fescue or the grasses and weeds allowed to reestablish themselves. '

Cultivation under the trees can affect nutrient level because it destroys the roots in the surface soil which is particularly high in K and P. Grass and weed competition are reduced by cultivation, thus soil moisture is conserved and N is more available because grass competes with the trees for N.

Sod Mulch

Mulching presents a dilemma in regards to orchard floor management. Hay mulch can suppress grass and weed growth, improve soil structure, conserve moisture, and is a source of nitrogen (N) and potassium (K). Soil contamination from soil sterilants such as terbacil, diuron, simazine, and dichlobenil will be reduced because they accumulate in hay mulch residue under apple trees. Calcium mobility might be greater under mulched trees because this element is carried by water. High K is favorable for red color development and the need of this element is high in heavy-cropping trees. Mulch is favored by individuals who prefer not to use commercial fertilizers. In contrast, mulch is expensive to purchase and/or apply, might not be readily available, and provides ideal nesting places for rodents. Excessive N and K supplied by the hay mulch can suppress Ca uptake. Thus, when apple trees are heavily mulched, it is necessary to adjust fertilizer programs, especially after the mulch commences to decay. While the material applied as mulch varies considerably in chemical content, the average hay mulch contains approximately 1% N. 0.4% P and 1.3% K. On this basis, 33 pounds of hay mulch is equivalent to 1 pound of ammonium nitrate in respect to the N added to the soil. The heavy application of mulch eventually adds large quantities of K and N to the soil. In addition to adding K to the soil, mulch makes more readily available the soil's supply of K.

Herbicides

Chemical weed control is a proven economical practice and now apple trees are commonly grown with herbicide strips and grassed alleys. Herbicide applicators must be trained to observe all safety precautions. Volatility and drift of sprays are serious problems because of damage to the trees and contamination of the environment. Transfer of herbicides to improper containers; failure to provide for the safety of orchard workers, children and animals; improper handling, storage and disposal of unused herbicides; and disposal of herbicide containers rank high among the problems and risks in chemical weed control.

Herbicide strips and grassed alleys present the trees with 2 distinct soil environments--with and without root competition from grass, and presents several cultural considerations. For the latest recommendations on chemical weed control refer to the current year's New England Chemical Weed Control Chart for Tree Fruits.

Considerable attention has been given to the effect of herbicides on nutrition. A number of workers have reported that sub-lethal concentrations of simazine will increase leaf N of apple trees. In contrast, in our field studies, no difference in nutrient levels or in growth of apple trees could be attributed to simazine. However, in greenhouse studies, we found that low concentrations of soil-incorporated simazine did increase leaf N of McIntosh apple trees grown in 30 lb. cans. We believe the lack of a response under our field conditions is because most of the simazine is absorbed by the organic matter in the upper 3 inches of the soil and not available to tree roots.

The effects of herbicide strips on root growth and nutrient uptake have recently received much attention in England and Europe. The studies at East Malling Research Station show that apple trees produce most of their roots in and obtain most of their nutrients from the soil of the herbicide strip. Root growth under the grassed alley appear deeper and more sparse.

Herbicides indirectly affect the nutrition of fruit trees because killing of vegetation under the trees reduces the competition between grass and tree roots for minerals and water. Furthermore, herbicides will decrease soil pH and adversely affect earthworm populations and thereby soil structure.

Mono-herbicide combination. Many orchardists use a tank mixture of the same herbicides year after year. The combination consists of a post-emergence herbicide which has contact or systematic activity plus a pre-emergence herbicide (Table 1).

Table 1. Classification of herbicides according to their mode of action.

Systemic Contact Soil sterilants**
Ammate X-N1 * dalapon paraquat terbacil
Dacamine 4D Glyphosate diuron
Dacamine *   simazine
Pennamine   dichlobenil
    napropamide
    oryzalin

 

* Trade names

** Soil sterilants are used as pre-emergency herbicides

The annual use of the same herbicides is simple and requires the least skill but has a number of weaknesses. The continual spraying of the same tank mix of herbicides permits the establishment of herbicide-resistant weed species since most herbicides are unable to control all noxious weed species (Table 2).

Integrated system. This system rotates combinations of pre-emergence and post-emergence herbicides that are complimentary in the weeds they control, increases crop safety and reduces herbicide build-up in soil (Table 2). Nevertheless, the age of trees and the weed species in the orchard cover can, and should dictate the herbicide program utilized as illustrated in the following examples. Young trees are less tolerant to herbicides than older trees probably due to the limited root system and "depth protection" of newly-set trees. Dalapon will control only grasses. The absence of a residual effect in soil from glyphosate and paraquat sprays may necessitate the use of pre-emergence herbicides. Most pre-emergence herbicides are ineffective in controlling perennial weeds such as poison ivy, brambles, bindweed and milkweed (Table 2). Glyphosate will control a broad-spectrum of weeds but spray contact with the tree other than with mature bark on the main trunk may result in tree injury. Lastly, simazine will not control dandelions whereas dichlobenil another preemergence herbicide, provides excellent control of this noxious weed.

Shielded sprayers, wiper applicators for "spot" treatments of problem weeds have broadened the use of non-selective, systemic herbicides. Pipe-wicks ropewicks. spongebars. rollers and mops make up the universe of wiper applicators. The most popular with orchardists is the sponge bar attached to a PVC pipe (a hockey stick wiper). The pipe is filled with a concentrated solution of glyphosate (25% solution).

Suppressing weed growth. Growers have become concerned about winter injury due to the absence of sod under their trees from annual use of herbicides. Of more concern is the occurrence of soil erosion and in some instances tree heaving. Therefore, growers have expressed interest in re-establishing sod and then suppressing grass and weed growth rather than eliminating this growth.

Dacamine*, Dacamine 4D*, paraquat or Dowpon*M (dalapon) appear to be the logical herbicides to use for re-establishment and maintenance of sod under apple trees. Where heaving of trees has occurred applications of mulch and re-establishment of sod may help prevent it.

The first year after herbicide applications are discontinued broadleaf weeds like cinquefoil, dandelions lambsquarters, ragweed, and plantain will probably be the predominant types of vegetation. If these weeds become troublesome by late-July or in August, Dacamine or Dacamine 4D can be applied under apple trees for their control without injuring grasses. Continue to use Dacamine or Dacamine 4D in subsequent years as needed under apple trees until grasses are re-established, then switch to dalapon or paraquat.

Table 2. Common problem weeds in orchards and herbicides for their control

1. Quackgrass--glyphosate, terbacil, dalapon and dichlobenil are most effective.

2. Horsenettle--glyphosate most effective. Some control with terbacil, paraquat, Dacamine*,

Dacamine 4D*, Pennamine D7*, and Ammate XN-1*.

3. Milkweed -- glyphosate most effective. Some control with Ammate XN-1*.

4. Bindweeds ("Morning glory") -- glyphosate, Dacamine*, Dacamine 4D* and Pennamine D7* are effective.

5. Dandelions -- Dacamine*, Dacamine 4D*, or Pennamine D7* are best for control in tree alleys. Terbacil, dichlobenil, glyphosate and Ammate XN-1* are best for control of dandelions under trees because of danger of tree injury from drift of fine spray particles and/or volatilization of Dacamine*, Damacine 4D* or Pennamine D7*

6. Poison ivy--Ammate XN-1* and glyphosate are both effective.

7. Vetch--a combination of paraquat and terbacil is best.

Dalapon is labelled for grass control at 5 to 10 Ibs. per acre under apple trees (use the low rate for trees less than 4 years old). Nevertheless 5 Ibs. per acre may be sufficient for apple trees of all ages. Trials in the past showed that this rate in some instances merely suppressed grass growth and in other instances. it eliminated 40-90% of the grasses. Therefore, the degree of grass control with 5 Ibs. per acre is not predictable. However, users of dalapon may find that lower rates are necessary under older trees where grass growth is less luxuriant than under young trees.

The re-established sod probably will be a mixture of grasses and broadleaf weeds; therefore, it may be necessary to control troublesome weeds with paraquat, Dacamine or Dacamine 4D since dalapon controls grasses.

A paraquat program alone also should be suitable for re-establishment and maintenance of sod. Apply in spring under apple when grass is 10-12 inches high. A repeat application may be necessary in mid July.

Studies by Hislop and Prokopy (Fruit Notes 44(5) :6-8) showed that dalapon had low toxicity to Amblyseius fallacis, the most important predator of red and two-spotted mites id commercial orchards in Massachusetts, and they suggested the use of dalapon as the herbicide in integrated pest management programs. In contrast, in earlier studies Hislop et al., (Fruit Notes 43(4) :5-8) found paraquat highly toxic to A. fallacis. These workers have not determined Dacamine or Dacamine 4D toxicity to A. fallacis.

Vertebrate Pest Control

The control of vertebrate pests in the orchard is a decision that most fruit growers will ultimately have to make. Because damage can delay the onset of production (e.g. deer browsing) or shorten the productive lives of trees (e.g. pine or meadow vole bark chewing), the success of vertebrate pest management can affect the apple crop for years to come.

Damage for the most part will take place during the winter months when access to the orchard may not be possible. Thus, it becomes necessary to look at the history of animal damage in the orchard and gather information on the various species of wildlife that have or could cause damage. This information will determine what actions should be taken to contain or prevent further damage by wildlife.

Meadow Voles

Description -- The meadow vole is a small, heavy bodied rodent with short visible ears and prominent black beady eyes. The fur is relatively coarse and dark brown in color. The total body length is approximately 5", and the tail length (approximately 13/4") exceeds the length of the extended hind foot. Both sexes are of similar color. Males are frequently slightly larger than females.

Life History--Meadow voles are capable of reproducing during all months of the year. During an average year a female will produce 8 to 10 litters, each litter consisting of 4 to 6 young. If food and cover conditions are ideal, the reproductive rate may be much higher. Young females may become sexually active at 4 months. The average life span of meadow voles is about 1 year or less.

Meadow voles primarily inhabit the ground surface and are found in a wide variety of habitats. Some of the more preferred areas are orchards, meadows and other areas with heavy grass, sedge, or legume vegetation. Although meadow voles will make and use shallow underground burrows the majority of travel is in surface runs.

Food habitats are variable with clover, dandelions and a variety of grass and sedge species included in their diet. As the soft vegetation becomes less abundant or less palatable these animals can and do feed on several types of woody vegetation, including bark of cultivated apple trees.

Injury -- Damage to apple trees may occur at any time of the year, but usually occurs during the fall and winter months. The majority of the damage to trees occurs at the base of the trunk beginning at the root collar and up to and including any low branches. Damage to upper trunks and branches occurs most frequently during periods of deep snow. Damage consists of patches of chewed bark with tooth marks at different angles,1i/8" wide,1/6" deep and up to l/8" long. In cases of severe injury the trunk of the tree will be completely girdled.

Monitoring -- The presence of this surface dwelling animal is fairly easy to determine as the constant travel of voles will develop a definite pattern of surface runways that are well packed and clean of vegetation. During the growing season piles of fresh grass clippings will be evident in the runways. Clippings are up to 1-1~/2" long and show definite tooth marks on the cut ends. Active runways in use can also be identified by the presence of fresh droppings.

To determine the presence of meadow voles, a series of flagged apple slices can be placed in the runway systems or in the 4 quadrants of a tree, under the drip line. Recheck these placements after 24 hours to determine if voles under that particular tree have chewed or totally consumed the apple slices. The degree of consumption will approximate the degree of infestation. The presence or absence of vole activity will determine the need and intensity of a control program.

A map of the blocks and individual trees sampled should be maintained along with the degree of activity for each apple placement. If a baiting program is required, a second series of apple placements should be put out under the same trees previously sampled approximately two weeks after poison bait application. The degree of vole activity measured during the second 24 hour placement when compared to that of the first will indicate the success of your control program and the need for any additional control measures.

Management--Unless preventive measures are taken, many orchardists can expect mouse damage to occur during the winter months. Most fruit growers know from past experience which areas or blocks of trees are likely to be damaged. However, it is still a good idea to check the orchard in the fall to determine the status of old problems and if any new trouble areas have developed. After identifying problem areas, a sound management program can be developed and put into operation which would include some or all of the following measures:

Barriers -- Tree guards should be installed on newly planted and young trees to protect them from mouse damage. One of the better materials to use is 1/2 inch mesh galvanized screen. The screen should be recessed into the ground as deep as practical and should extend up the trunk to the first set of limbs to afford as much winter protection as possible. The screen must have sufficient overlap around the tree to allow for future growth. During seasons of heavy snowfall, trampling down snow accumulation around wire guards may be needed if mouse populations are high to prevent damage to trees as mice feed on top of snow and above mesh barriers.

Vegetation Control--Control of vegetation by mowing limits the number of voles by reducing the amount a cover needed for their surface runways. Vegetative cover should be removed not only from between rows and trees but from areas under each tree as well. Mowing equipment should be of a type that does ,not leave a thick mulch layer after the operation, so that rotary mowers are preferable to sickle bar mowers. This mulch-like layer of vegetation, if left may attract and concentrate voles. Ground cover may be eliminated by clearing a 3 foot radius of vegetation around the base of the tree trunk by cultivation, or chemical weed killers. The use of herbicides, including dosages and methods of applications should be according to label instruction. (Consult your Extension Fruit Specialist for more information .)

Cultural practices have definite limitations and should not be relied on as a complete control program for meadow mice. Vegetative control may not be effective during winter months when there is snow cover.

Toxic Baits--Currently there are several toxic baits commercially available. the primary application select one and follow the recommended rates on the label. If a second application is necessary consider using a different orchard mouse bait. If the mouse population is low the highest application rate of bait may not be necessary.

Since all baits will be affected to a degree by wet weather, applications should be made with a reasonable assurance of 72 hours without rain. The recommended time of bait application is after harvest. Usually during the month of October, but before snow fall.

To be effective, orchard mouse control materials have to be placed so that voles can find them. This is typically not a problem with hand or machine bait placements. When baits are broadcast however, the condition of grasses and other vegetation on the orchard floor can be very important. Mowed vegetation, particularly if it is tall and thick will fall in a mat and prevent broadcast bait from getting down to the soil level and runways where it is most effective. Therefore, it is often best to bait first and mow later.

Matting of vegetation will also be present under trees shortly after picking, caused in this case by harvesting crews working around and under the trees. To enable broadcast baits to reach soil surface, a week or two should be allowed after harvest for the vegetation to recover and for the mice to re-establish their travel systems. After the bait is applied mowing can then work to the growers advantage by providing protective cover for the bait and giving the mice the cover they require.

Hand Baiting--Examine the orchard floor systematically for distinctive trails made by mice. Fresh grass clippings and droppings in runways are evidence of activity. Abandoned runways may have thread-like fungus growth, green grass shoots, and the general appearance of non use. When baiting. glance ahead to locate probable spots for bait placement. Examine one side of a tree, looking for runways in heavy cover under the drip line and move in toward the tree base until either an active run is found or a tree is considered inactive. Disturb the area as little as possible.

Bait Stations -- One modification of hand baiting is the use of baiting stations under the trees. These stations can be of any material such as asphalt shingles. ]/2 tires or wooden box ends placed under each tree. Bait stations should be placed in the spring. This gives the voles ample opportunity to locate and build runways under the placements. During the fall baiting season stations are then lifted and a prescribed amount of bait is applied.

Broadcasting Bait -- Broadcasting bait by airplane. tractor-drawn seeder or fertilizer speeder can produce good results and will reduce time and labor costs. All equipment must be calibrated to dispense the proper amount of bait per acre. With the exception of bait distribution by aircraft most ground equipment can be adjusted to place baits in the tree row were it is most needed. Other considerations important when broadcasting baits have been previously discussed.

Trail Builder--The Trail Builder is a machine that makes an artificial burrow, approximately three inches below the ground surface and automatically dispenses bait into the runway at regular intervals. Commercially-made Trail Builders usually reduce labor costs and are more efficient than homemade machines. They are most effective in light loamy soil and with sod conditions conducive to making a clean, smooth trail.

Migration and Buffer Strips -- Growers should realize that a meadow vole population is not static. Populations constantly change and under some situations the vacuum or void created by regular vole control will be filled by animals moving in from elsewhere. This frequently happens when a block of trees is adjacent to unmowed fields. Mice frequently move into the orchard under the snow cover.

To reduce the chance of mice immigrating into a treated orchard, buffer strips may have to be considered. This is particularly important for those tree blocks abutting heavily-grassed areas. Vegetative control by cultivation, herbicides or bait treatment of these strips will increase the hazards and distance that meadow mice will have to travel before they reach the orchard.

Caution -- Before carrying out these recommendations, check the legality of the method in your state. In all cases check the label before using any toxic material for mouse control to insure proper and safe usage. Toxic baits should only be used where children, irresponsible persons, pets, livestock, and desirable wildlife are adequately protected. Avoid breathing the dust and wear gloves when distributing bait. After use, carefully wash hands and utensils. Store the poisoned bait and contaminated items in a safe and well-ventilated place in accordance with safe pesticide storage practices.

In Massachusetts, a permit from Massachusetts Division of Fish and Wildlife is required before toxic baits can be used. Similar permits may also be required in other states.

Read and Follow the Label Instructions Carefully

Pine Voles

Description--Pine voles are similar to meadow voles in general appearance. The body is the same general shape but smaller in size. The body length is about 3-31/2". The tail is approximately 1" or less and always equal to or shorter than the extended hind foot. The eyes and ears are small and the fur is smooth, fine in texture and a rich brown color. Both sexes are similar in color and size.

Life History -- The reproductive season for these voles in New England extends from February into November. Unlike the meadow vole this animal's reproductive potential is only 1 or 2 litters a year consisting of 2 to 4 young per litter. Young of the year become sexually active at about 2 months. The average life span for pine voles is probably 1 year or less.

Pine voles spend the majority of their life living and feeding in underground burrow systems. Although found in a wide variety of habitats, they prefer woodlands or grasslands having well drained soils suitable to the digging and maintenance of burrows. Soil structure is probably a limiting factor in their movements. Burrow systems may be extensive and vary from just under the soil surface to a depth of 10-12 inches. In orchards the majority of these burrows are within the drip line of apple trees. The diameter of the burrow is 1 to 2 inches.

Food habitats are variable and probably opportunistic with indications that the stems and root systems of grasses and other plants are a primary summer food. As seasons progress additional use is made of fruits, seeds, barks, tree and shrub roots. Fall, winter and early spring are the times of year when the most damage to apple tree root systems occurs.

Injury--Since the majority of feeding is underground, damage is not readily observed and frequently shows up as weak trees or sprouts from damaged roots. Large roots may be peeled of bark and cambium and smaller roots can be completely consumed. Heavy feeding will kill younger and smaller apple trees in one year.

Monitoring--The underground habits of these animals make it extremely difficult to monitor their presence and determine relative numbers. There are however. some signs that can be used to determine the presence of pine voles.

Examine under the drip line of trees by probing the ground with extended fingers to locate underground burrows. Carefully excavate a runway to determine if it is active or not.

During mid-September into October look for fresh piles of soil under suspected trees. These soil piles will be most evident after a tree has been picked and will indicate pine vole activity caused by the cleaning out of burrow systems.

If trees are known to have pine voles or if burrows of unknown age are found the flagged apple slice method described under meadow voles can be used to confirm activity. Instead of using surface runs, the slices are placed in the pine vole burrow systems. The section of burrow systems to be used should be cleaned out and disturbed as little as possible during apple placement.

Since pine voles will clean disturbed burrows and plug any openings this sign can also be used to determine the degree of activity in addition to any chewed or consumed apples.

Management--(Review management methods under meadow voles). Since pine voles are a burrowing animal and live most of their lives underground broadcast baits will only be partially effective. The most effective method of bait application is careful hand baiting of burrows or the use of a trail builder machine. The same bait materials available for the control of meadow voles are suitable for pine vole control, only the method of application will vary. i

Control of vegetation by dishing. sod chopping and herbicides in tree rows may provide some control since these techniques remove food supplies and/or disturb burrow systems. The effects of these treatments must be maintained over long periods to achieve any degree of pine vole control.

Caution -- When using toxic baits. read and follow label recommendations on application rates. Review legal requirements discussed under meadow voles.

Deer

General Information -- The white-tailed deer is one of New England's largest game animals. Throughout some of its range' deer populations have generally increased in the last few years. Much of this increase is due to human activity, such as logging, which has changed vegetation patterns. These changes have provided new habitat and increased the overall food supplies for deer.

The deer is a strict herbivore feeding during the colder months on a variety of twigs and buds of trees and shrubs. Some of the more preferred woody plants are maples, oaks, dogwoods, sumac, blueberry and spireas. As a herd increases, the density of deer in an area will determine the food priority. As the more desirable browse disappears other types will be used more frequently. It is during these periods of higher population and decreasing availability of highly preferred foods that apple and other commercial fruit trees are most susceptable to browsing damage. This is particularly true if the orchard is surrounded by woodlands that harbor deer during the winter months.

Injury -- Under most conditions feeding takes place during the early morning, late afternoon or evening. Under severe stress the deer will feed in some portions or fringes of the orchard with greater frequency during other times of the day. Damage to fruit trees may be limited to a few trees or, under severe conditions, cover large areas. Damage for the most part will be restricted to areas close to the deer's escape cover.

Browsing damage by deer can be identified by its rough and ragged appearance. Deer, unlike rodents and rabbits, do not have upper incisor teeth. They cannot cut the twigs cleanly, and instead must tear and twist the material from the branch. Twigs up to /" diameter are browsed with damage 3' to 5'from ground level. Repeated browsing will lead to a brushy appearance as the plant sends out new growth. Although heavy damage is very apparent, detection of lighter browsing activity may depend on signs of deer presence such as tracks or droppings.

Monitoring--Monitoring should be an essential part of a deer control program. Since existing control methods tend to be expensive and labor intensive it is necessary to determine when damage becomes an economic problem. When does the damage to trees and the resulting crop loss exceed the cost of selected control measures?

Accurate records over a period of time (years) will help growers decide when it is cost effective to control deer damage. On an annual basis the location of damage, number of trees, degree of injury per tree, time of year when damage is likely to occur and estimated crop loss should be recorded. Additional information on changes in deer numbers in an area, the proximity of a winter yard to the damaged area and even snow depth and other weather conditions which could effect deer movement will also assist in the decision making process.

By examining the past history of damage a grower should have a good idea what to expect during the upcoming winter season. Applications of a chemical or mechanical control measure are always more effective if done before damage is likely to occur.

Management -- Several techniques of managing deer are used, including:

Repellents -- A wide variety of materials have been used over the years with varying degrees of success. There has been some use of noise and scare devices, but for the most part they are ineffective during the winter months.

The majority of repellents in use today are chemical, either those commercially available or of a homemade variety. Since home remedies are so varied they will not be discussed.

Commercial chemical repellents for fruit trees include the fungicide thiram, ammoniated soaps of high fatty acid, putrescent whole eggs and bonetar oils. Classified as taste and/or odor repellents, all are applied by spray, brush or dip either directly to the plant or the ground around the plant. All have to be applied at temperatures exceeding 40 . Resulting control can and does vary a great deal with chemical repellents.

To achieve the best possible results the label directions should be strictly followed. Application of chemical repellents should take place after harvest when trees are dormant, but before deer damage occurs. With all animal problems it is easier to prevent damage from occurring than it is to stop damage that is underway.

Typical winter weather of rain, snow and sleet will erode the repellent over a period of time and reduce its effectiveness. This erosion may be severe enough so that by the time the chemical is most needed it is not sufficiently available to do the job. If the repellent to be applied does not include a sticking agent one should be added to the mixture before use.

Growers should also realize that, as winter progresses and preferred foods are consumed, deer will feed on other trees and shrubs no matter how bad they taste or how low its food value. It becomes a matter of survival.

Fences -- The use of a well designed fence is perhaps the growers best protection against deer damage. In determining the use and type of fence a grower will have to make certain decisions relating to cost and effectiveness. Of primary importance is whether the cost of the fence will be offset by the increased production being lost to deer. By prorating the initial cost and maintenance over the life span of the fence the use of this control measure may be feasible.
There are several requirements that have to be met for any fence to be effective. By preference, deer will crawl under or through a fence rather than jump over it. Consequently all fencing has to be kept tight and close to the ground. For electrified fences the bottom wire can be up to 10" from ground level. All non-electrified fences have to be at ground level and staked, and a minimum of 8' high.

To be effective there should be a cleared area on the outside of the fence for 4 or more feet. This cleared area reduces the tendency of deer to jump the barriers. Some electrified fences require control of vegetation at the base of the fence to prevent shorting out of the critical bottom wire. In some areas the normal snow depth and drifting have to be considered. In areas where snow depths are normally high and drifting occurs the fence may be buried and its barrier effect lost when it is most needed. All fences require periodic maintenance. If wires are loose or the fence is damaged or broken it is ineffective.

There are currently several types of fence designs which should be considered by growers.

1. 8-foot woven or stock fence, with or without an electric wire outrigger.

2. 5 wire vertical electric deer fence (Penn. State design) requiring high-tensile steel wires and a high voltage, low impedance energizer.

3. 7 wire high-tensile steel sloped deer fence. This also requires a high voltage, low impedance type energizer.

4. New Hampshire figure 4 electric fence. Normally not over 4' high but may be effected by vegetation and snow. Uses a standard fence charger and is primarily for summer use.

5. Individual tree fence. This may be a snow fence or woven wire staked around individual trees.

Herd Reduction -- In Massachusetts and the other New England states the white-tailed deer is a managed game animal. During the fall there will be a regulated period when hunting is permitted. If you have a deer problem consider working with the local deer hunters and permit the harvesting of deer in the orchard area. The removal of a few deer may be all that is needed to reduce damage to an acceptable level.

Cottontail Rabbits

Damage by these animals is highly variable by year and usually localized within the orchard. Damage is usually not severe except during winters with deep snow when natural foods are scarce. Areas of rabbit damage will be adjacent to normal rabbit cover such as overgrown ditch banks, stonewalls, brush piles and other brushy areas that provide cover.

Damage usually occurs during the twilight and night time hours. Damage is seldom more than 2.5 feet above the ground or the highest winter snow level. The height of damage will increase with increasing snow depth.

Injury--One type of injury consists of clipping of small twigs, branches or buds. Material removed is usually l/4" in diameter or less. The cut is smooth and angular rather than the ragged type caused by deer.

A second type of injury will be the debarking of limbs and tree trunk. This type of damage is usually in patches. On hardwoods such as apple trees, gnawing is usually clean and will show incisor marks.

Monitoring -- Like deer damage, the past history and location of rabbit damage over the years may be the growers best indication of what to expect. This past history plus late fall checks for rabbit signs in known problem areas may be all that is needed to determine the need for control.

Management--Cottontail rabbits prefer dense thickets or heavily vegetated areas in which to live. Cover of this type is necessary for food and protection from predators. Rabbits leave cover at night or early morning, feed in crop areas, and return to the thicket for protection during the day. Habitat control by mowing, brush cutting, and general cleanup of overgrown areas may be all that is needed for rabbit control. Without sufficient cover, rabbits do not stay in exposed areas.

Tree Guards--Tree trunk guards are also effective in preventing rabbit damage to trees or shrubs. These guards should be of a material heavy enough to prevent rabbits from chewing through it. Tree guards of various types are available from commercial sources.

Repellents -- Taste repellents are another method of reducing rabbit damage. When properly applied, repellents make treated trees less desirable as food. Three factors determine the effectiveness of the repellent: (1) thoroughness of the application; (2) weather conditions, and (3) proximity of existing rabbit food and cover. The entire area of the plant susceptable to damage must be completely covered. The application must be heavy enough to withstand adverse weather conditions, since frequent rains and snows erode and dilute the material and reduce the amount of protection the repellent offers. Retreatment may be necessary during late winter to provide continued protection. For further information on repellents refer to repellent section under deer.

Population Control -- In areas having a high rabbit population and a constant history of injury, rabbit damage to trees may be reduced by hunting. During the legal hunting season. local hunters should be encouraged to hunt rabbits in these areas.

Porcupines

Porcupine damage to fruit trees is only an occasional problem. When it does occur, however, damage can be several. Damage is usually very localized and restricted to a few trees adjacent to wooded areas. Most damage occurs during the winter or early spring when these animals are concentrated in winter dens. Damage tends to be persistent occurring year after year and to the same trees.

Injury--Porcupines are excellent climbers, consequently damage may occur anywhere on the tree. The main trunk and large limbs from base to crown may have large sections of bark removed. Damaged areas will have both horizontal and vertical tooth marks. The average width of incisor mark is .10 inches.

Clipping and cutting of twigs and smaller branches frequently occurs with branches up to 3/4 inch removed by a slanting cut. Clipped branches and twigs will be found under the tree. Near harvest porcupines will also climb trees and feed on fruit on the tree, leaving only the apple core hanging.

Management--Repellents are not effective on porcupines, so that habitat and population control measures must be relied upon. Porcupines tend to concentrate and use the same winter dens each year. The travel distance from these dens is usually not more than 300 feet. After a fresh snowfall, these animals can be easily tracked from tree to den or vice versa and the offending animal can then be shot or trapped (note in some states only live traps may legally be used). If their den is in a tree, stonewall or a single opening in a ledge, consider removal or blocking of the den to prevent future use.

Acknowledgements

The authors wish to thank the following individuals who reviewed the manuscript and offered numerous helpful suggestions.

Dr. T. Burr, (NYSAES, Geneva, N.Y.)

Dr. R. Weires and Dr. D. Rosenberger (Hudson Valley Lab., Highland, N.Y.)

Dr. A. Eaton, Dr. W. MacHardy (University of New Hampshire, Durham, N.H.)

Dr. R. Adams (University of Connecticut, Storrs, CT)

Dr. J.F. Dill (University of Maine. Orono. Maine)

Dr. A.L. Jones (Michigan State University, E. Lansing, Michigan) and

Dr. G.N. Agrios (University of Massachusetts, Amherst, MA)

Special thanks to Priscilla Coe for typing the manuscript.

All photographs are by the authors except: White apple leafhopper adult, two-spotted mite, San Jose scale crawler and apple blotch leafminer adult (Cornell University). Life Cycle of Apple Scab. Physalospora, and Life Cycle of Cedar Apple Rust (Courtesy of Academic Press, Inc., N.Y.. N.Y.) Powdery mildew and black rot symptoms (Courtesy Cooperative Extension Service, Clemson University)

This publication is supported in part by a grant from the United States Department of Agriculture. Cooperative Extension Service. Office of IPM Programs.

Copyright 1989