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Diseases and Insects Pests of Cereals in the Atlantic Provinces

prepared by the Atlantic Advisory Committee on cereal crops 1982
by: R.A. Martin and H.W. Johnston
Agriculture Canada, Charlottetown
Prince Edward Island
for the Advisory Committee on Cereal and Protein Crops.
Certain photographs appear in this publication courtesy of the American Phytopathological Society, and U.S.D.A. and Agriculture Canada personnel.
82-6M.

 

  • CAUSES OF PLANT DISORDER
  • CONTROL MEASURES
  • DISEASES
  • INSECTS
  • CONTROL MEASURES
  • INTRODUCTION

    Cereals grown in the Atlantic Provinces are subjected to a wide variety of disease-causing organisms, pathogens, and insect pests which can dramatically reduce yield and quality of the harvested grain. The spectrum of disease problems is usually constant from year to year but weather conditions will frequently alter the severity of particular diseases. Cereal grains are normally damaged as a result of multiple infections, although damage by a single disease or insect pest can be severe. The occurrence of multiple infections makes identification of the problems difficult, but growers who regularly inspect their crops will be able to recognize abnormalities based on the time of appearance and symptom expressions. In order to reduce the damage caused by diseases and insects, it is necessary to recognize and identify the problem early in the developmental phase so that appropriate control measures can be taken. Once a crop has been damaged it is seldom possible to recover that which has already been lost to a disease or insect, through the application of control measures. Complete control of a problem is seldom possible, however much potential damage is preventable.

    This booklet has been published for Atlantic grain growers to aid in the identification of the major diseases and pests of cereals in Atlantic Canada and to provide recommendations for their control.

    CAUSES OF PLANT DISORDERS

    Damage to cereals may be classified by its causes. Fungi, viruses, bacteria, and insects are all types of organisms which may depend on the plant for survival during part of their life cycle and in so doing cause adverse effects to the plant. Other factors such as moisture, temperature, soil fertility, and soil pH can also result in damage to cereals and losses to yield and quality.

    Fungi

    Fungi or molds are very small organisms which cause most of the infectious cereal diseases occurring in the Atlantic Provinces. Their reproductive bodies or spores are frequently wind borne and are thus easily transmitted from plant to plant. Once established within a plant, they reduce yield and quality by impairing the normal functioning of the host plant. Each fungus, causing a particular type of symptom or disease, has different requirements for its life cycle. In order to devise methods of control it is necessary to identify the fungus, establish how and when it invades a plant, how it impairs the plant's normal functions, and how it reproduces or survives from year to year. Most fungi causing cereal diseases overwinter or survive between crops on seed, stubble, crop debris in the soil, and/or alternate hosts. Fungal diseases are identified in the field by the kind of symptoms or discolorations appearing on the plant and by signs of the casual fungus.

    Viruses

    Viruses are minute agents, not visible to the naked eye, which are inert when outside a host cell, but once within they multiply, become infectious, and interfere with the normal functioning of the host plant. The virus particles usually spread from plant to plant by insect vectors which transmit the viruses as they feed on cereal plants. Aphids are the most frequently encountered insect transmitters of cereal viruses found in the Atlantic Region.

    Bacteria

    Bacterial diseases are not of widespread importance in the production of cereals in the Maritimes and are not covered in this booklet.

    Nutrient Disorders

    Factors such as moisture, temperature, soil fertility, drainage, and soil pH, when in excess can result in losses of yield and quality. Soil fertility, pH, and drainage are factors which should be considered prior to planting and where necessary corrected so as to maximize yield.

    CONTROL MEASURES

    Most practical control methods prevent the occurrence of a problem or lessen its severity rather than eliminate the problem, once it has occurred.

    The following methods are general recommendations which apply to a number of diseases in the same crop and should be used together, when possible. This involves the integration of several control measures so as not to rely on a single method.

    Resistant Varieties

    Resistant varieties should always be employed when available and agronomically suitable. Complete resistance is not always available for all of the disease problems encountered, however partial resistance to some problems may be available. Partial resistance may enable a successful crop to be produced while susceptible varieties may only be suitable in years when the environment is unsuitable for disease development. Publication 100A, Field Crop Recommendations for the Atlantic Provinces, should be consulted for currently recommended varieties for the region.

    Crop Husbandry

    Good cultural practices promote vigorous growth in plants. Recommended seeding dates, fertilization, liming, and good seedbed preparation will help to ensure successful crops. Early seeding of spring cereals is one method which is usually successful in avoiding serious disease losses. The earlier a spring cereal is planted the more mature it will be when diseases or insects attack and will therefore sustain less damage.

    Crop Rotation and Field Sanitation

    Rotation of cereals with non-cereal crops such as legume forages is a sound practice which prevents the build-up of many cereal pathogens and pests. Many grass weeds are hosts for cereal diseases and insect pests and thus a successful rotation should eliminate these alternate hosts. Quackgrass is one of the most important alternate hosts for cereal diseases and pests. Fields and headlands should be maintained weed free. The most successful cereal rotation is one in which a non-host crop is produced before and after each cereal crop. Occasionally, cereals are produced for more than one year on the same land before it is taken out of grain production. This practice is not recommended.

    Field sanitation means the destruction of stubble and crop debris on which disease causing organisms and insect pests may overwinter. The best method to reduce the amount of surface crop debris is to incorporate it into the soil as soon as possible after harvest. This will allow soil microflora to develop in warm soil and provide time to decompose crop debris and thus prevent pathogens from overwintering. When considering fall plowing and additional fall cultivation, serious thought must also be given to potential soil erosion problems.

    Seed Quality

    Cereal producers are advised to always sow high quality seed. To obtain good quality seed, crops should be harvested at the proper maturity, cleaned, dried, and stored under proper conditions. Good seed should have low levels of contaminating fungal pathogens and be capable of germinating quickly to produce vigorous and rapid growing seedlings. A germination test should be carried out before seeding. Certified seed is recommended as it is an assurance of quality and varietal purity. Seed cleaning and treatment with a license fungicide is highly recommended for all seed used in the Atlantic Provinces.

    Fungicides and Insecticides

    A seed treatment is the application of a pesticide (fungicide and/or insecticide) to the seed to provide protection for the developing seedling from diseases and insects. The duration of this protection varies with the nature of the material used. In some instances the disease control potential of a fungicide may last through most of the plant's life. Some seed treatments reduce the severity of foliar diseases and control the smut diseases at the same time. Use of an appropriate fungicide applied to the foliage may be warranted in some instances. For further information regarding fungicides and insecticides used on cereals, consult the Field Crop Guides for the Atlantic Provinces, publications 100 and 100A.

    DISEASES

    1. Seedling Blight, Common Root Rot, and Spot Blotch

    All of these barley diseases are caused by the same fungus. This fungus, Bipolaris sorokiniana, can be serious at any stage of barley development, resulting in reduced stand and in low yields of inferior quality grain.

    Seedling blight and common root rot are problems which are continuous throughout the growing season. Seedlings which are heavily infected may fail to emerge or damp-off soon after emergence. First signs of infection are brown discolorations at the base of the seedling which can spread to both leaves and roots. Roots of infected plants will be poorly developed and will have a dark brown discoloration.

    Spot blotch refers to the above ground symptoms. Symptoms on the leaves are observed as well defined oval to elongated dark-brown to black lesions, which may coalesce to form irregular spots. Lesions can be surrounded by healthy green tissue or by chlorotic, yellowish tissue. Foliar infections can occur at any time but usually begin appearing in early to mid-July. Heads and developing seeds are also attacked. infection of the seed, commonly known as black-point, is evident by black areas at the ends of the kernel. Foliar infection requires long periods of wet weather at moderately high temperatures (20 C). With severe infections, plants are stunted, leaves die prematurely, seed is small and discolored at the tip, the base of the plant is rotted, and the root system is poorly developed.

    The fungus can overwinter in the soil, on crop refuse, on the seed, and/or in susceptible grass weeds, such as quackgrass. Seed- and soil-born spores are responsible for seedling and root infections. They are probably also responsible, in part, for initial foliar infections. Other cultivated and non-cultivated grasses can also contribute to foliar infection by acting as a source of the disease-causing organism.

    Seed with a minimum of contamination should be used. It is recommended that seed be treated with a suitable fungicide to reduce inoculum, that is, the amount of the fungus initially present on the seed. Elimination of grass weeds, especially quackgrass, from within the field and from the fence rows, and crop rotation away from cereals are important methods of reducing infection sources. Good soil fertility will also reduce some of the effects of seedling and root infection.

    2. Take all

    Take-all is a fungal disease which is most damaging to wheat, barley, and rye. Oats, which does not exhibit symptoms, and other cultivated and non-cultivated grasses, enable the pathogen to survive between cereal crops. The fungus, Gaeumannomyces graminis, can overwinter in soil on diseased, undecomposed stubble, and roots of diseased host plants. Take-all is usually most damaging in situations of continual cereal production or where poor weed control is evident in the rotation.

    Diseased plants usually appear in localized areas of a field. These areas increase in size with each successive cereal crop. Infected plants are usually stunted with reduced tillering and are most conspicuous at heading at which time they become prematurely bleached and mature appearing. Heads are usually straw colored and empty. Roots are poorly developed and exhibit a dry black rot. If the lowest leaf sheath is pulled back a black fungal mat is evident. This blackening of basal stalk tissue is the best field diagnosis for Take-all. As the remainder of the crop matures, Take-all plants are often infected by non-pathogenic fungi which give a black, sooty appearance to the heads.

    Long crop rotations will reduce the amount of the Take-all fungus present in the soil. However, it is also necessary to control weed grasses in the field and fence rows which can act as reservoirs for future infections. Use of good seed and adequate fertilization will increase root growth and vigor and reduce the severity of Take-all. Plowing down the stubble promotes rapid decomposition of the pathogen's food base.

    3. Net Blotch

    Net blotch is a fungal disease, caused by Pyenophora teres, and is common to most barley fields in the Atlantic Region. Early symptoms of net blotch are light green to brown patches near the leaf tips. Blotches develop which are dark brown and have a cross-hatch pattern, vertical and horizontal lines within the lesions, giving the characteristic netted appearance. Lesions will spread across the leaf or extend longitudinally, confined between veins. The latter type of blotch appears as a dark netted stripe down the leaf and can be several centimeters in length. Early symptoms are often similar in appearance to spot blotch. The area surrounding the net blotch lesion will often yellow and if lesions are extensive the leaf will wither and die. Stems may lack strength and be more susceptible to breakage. Small blotches may also develop on the head, and along with leaf infections, cause lower yields and a low seed.

    Stripe disease of barley is similar to net blotch. However, with barley stripe, lesions spread into the leaf sheath from the leaf. Leaf tissue will also split and shred. Severely infected plants will also be stunted.

    The net blotch fungus is favored by cool, humid weather. It is, therefore, of particular importance in the spring and fall. This fungus overwinters in the seed and on crop residue in the field. Foliar symptoms can originate from infection of seedlings by mycelium of the seed-borne fungus or by wind-borne spores produced on stubble and straw within the field.

    Six row barleys usually show fewer symptoms than two row barleys. No barley cultivar, however, is totally resistant to the disease. Crop rotation and plowing down barley stubble and crop residue will reduce the number of air-borne spores. Recommended seed treatments will also reduce infection of seedlings from infected seed.

    4. Leaf Stripe

    This is a fungal disease of barley, caused by Pyrenophora graminea, which is not, at present, common in the Atlantic Provinces. It is however a disease which in the past few years has reappeared in Western Canada and one which could be imported into the region.

    Leaf stripe at some stages is very similar to net blotch in symptom expression. Lesions appear as yellow or brownish stripes on the leaf. These stripes will usually extend from the tip to the base of the leaf and are confined between leaf veins. As the disease progresses a longitudinal tearing of the leaf will occur. Plants may also be stunted.

    The fungus which causes leaf stripe has a life cycle similar to the fungus which causes net blotch. The control recommendations are therefore similar for the two diseases, see the section on net blotch. As the fungus is seed borne it is important to use clean disease free seed which has been treated.

    5. Scald

    Scald is a disease common to both barley and rye. Other cultivated and weed grasses may also be infected by this fungus, Rhynchosporium secalis.

    This disease is characterized by lesions which appear as oval to irregular blotches on the leaves and sheath. Individual lesions range in size from 5 to 25 mm in length and merge to form even larger blotches which totally girdle the leaf. Once girdled that portion of the leaf above the lesion is no longer of any benefit to the plant and will wither and die. Early lesions have a water-soaked appearance and a bluish green to pale grayish-green coloration. The center of older lesions progress from a brownish color to a bleached straw color. On barley the margin of the lesions will be a deep brownish color while on rye it is straw color.

    Scald, favored by long periods of cool damp weather, results in infections being most severe on very early seeded spring barley and on winter barley. Moderate infection early in the spring may be of little significance on yield. However, if the cool moist weather continues through late June then infection can be severe. Severe scald infection can result in yield losses in excess of 20%.

    The fungus, Rhynchosporium, overwinters on infected leaves and crop residue. In the spring the fungus produces spores which are carried in the air or by rain-splash to new growth. These spores infect new growth which then acts as a source of spores for further infections. Spore production and infection continues until the hot summer months when the spread is held in check. Infection and spread will restart in the fall when cool damp weather resumes. Volunteer plants and other grasses can also become infected. Seed can also act as an infection source.

    Control measures which eliminate or suppress the sources of inoculum are effective in controlling scald. Crop rotation, good field sanitation and elimination of crop residue is recommended. This includes plowing down stubble and controlling volunteer plants and grasses in the field and fence rows. Resistant cultivars may also be employed. Seed should be treated with a recommended fungicide.

    6. Powdery Mildew

    This fungal disease is frequently found on spring and fall seeded wheats but seldom on oats or barley. The fungus, Ecysiphe graminis f.sp. tritici, overwinters on stubble or winter wheat either as mycelium or overwinter fruiting structures called cleistothecia. The fungus can be found on stems, leaves, and heads resulting in a loss of plant vigor. The earlier the infection takes place, the greater the yield losses.

    Initial symptoms appear as small fluffy white spots on the leaves. This fluffy material, consisting of mycelium bearing summer spores of the fungus, may be easily rubbed off the leaves, leaving behind a yellowish area. These lesions later enlarge and take on a flowery appearance. Small black flecks, the overwintering fruiting bodies, can be seen within older lesions. The disease is more severe when winter and spring wheats are produced in the same area. High nitrogen (N) levels enhance disease severity but the disease may be reduced when phosphorus (P) and potassium (K) levels are adequate.

    Control of powdery mildew may be achieved through the integration of a number of methods. A number of resistant varieties are available and should be used when suitable. Field sanitation to reduce crop debris on the soil surface and keeping winter and spring wheat as far away as possible from each other is recommended. Crop rotation including cereals will aid in lessening the ability of the fungus to survive between wheat crops. Use of a recommended foliar applied fungicide may be warranted, particularly when high nitrogen levels are used to increase protein content and yield of seed. Certain fungicide seed treatments have the potential to control powdery mildew.

    7. Septoria Leaf and Glume Blotch

    These two diseases of wheat are caused by the same fungus, Septoria nodorum. Leaf blotch refers to foliar infections while glume blotch refers to head infections.

    Leaf blotch is most critical when the flag leaf, the first leaf below the head, is infected. Early symptoms are small light green to yellow lesions. Usually lesions appear on lower leaves prior to upper leaves. The lesions will enlarge to form large, irregular shaped, light brown to reddish brown blotches which may have a yellowish margin. Small dark colored specks, spore producing structures, will usually appear in the center of maturing lesions. Severely infected leaves will yellow and die prematurely. The fungus can also infect leaf sheaths and stems, especially at nodes, and thus severely reduce the plants resistance to node breakage and lodging.

    Glume blotch refers to infection of the glumes, or chaff. Early symptoms are small, irregular, light brown lesions on the glumes. With age these lesions enlarge and taken on a deeper brown color. Older lesions are lighter in color with numerous dark specks, the fungal fruiting bodies. Often, only the upper portion of the head or several glumes are infected. Infected heads may produce shrivelled and lightweight kernels or no kernels.

    The fungus overwinters on infected wheat stubble and volunteer wheat plants. Seed can also serve as a source of infection and may be one of the more important sources when seed produced from infected heads is used. Spores are produced in the spring during wet periods and are dispersed by splashing and blowing rain. Infection of plants is favored by wet weather and warm temperatures, 20-25 C. Some weed grasses may act as sources of inoculum but are of only minor importance.

    Control of both leaf and glume blotch is largely dependent on the use of clean fungicide-treated seed and good field sanitation. Rotation out of wheat for several years will reduce the inoculum in the field. Plowing down stubble and volunteer wheat plants should reduce Septoria during the following year. When warranted, foliar applied fungicides may also be beneficial.

    8. Septoria Speckled Leaf Blotch and Black Stem

    These diseases occur on oats throughout the Atlantic Region and are caused by the same fungus, Septoria avenae f. sp. avenae. Conditions required for disease development and control are similar for both. They are present each year and can cause significant losses in both yield and quality. In many respects, speckled leaf blotch is very similar to leaf blotch of wheat caused by Septoria nodorum.

    Foliar symptoms of speckled leaf blotch first appear in mid-June as purplish brown spots. These spots enlarge and coalesce into tan colored lesions. In late summer, the stems become infected and show blackened areas. These areas are weakened and thus lodging of the crop is enhanced.

    Control of speckled leaf blotch and black stem is similar to the control of leaf and glume blotch of wheat. Control is partially achieved through field sanitation and crop rotation with non-cereals. Incorporating stubble and crop debris will reduce Septoria inoculum in the following season. There is a low level of resistance in some cultivars. The use of a recommended fungicide seed treatment will reduce the seed transmitted phase of this disease.

    9. Fusarium Head Blight and Stem Breakage

    Fusarium head blight, as caused by Fusarium graminearum, is a fungal disease which appears on all cereals but is most noticeable on spring wheat. In some years, Fusarium head blight has had dramatic effects on cereal production in Atlantic Canada. This disease results in severely blighted or premature death of the heads, low grain yields of very poor quality, and possible contamination of the grain with toxins. The pathogen has a wide host range including some forage and wild grasses. The fungus may attack roots and stems, as well as heads.

    Symptoms on wheat usually appear in late July with one or more spikelets ripening prematurely thus appearing bleached in coloration. This coloration spreads and the entire head may be infected with complete fields appearing blighted. Wheat and barley heads and oat panicles gradually taken on a pink to salmon coloration. If the stem within the head or rachis becomes infected, the head above the infection will die. Individual seeds which have been infected may have pinkish discolorations or be white.

    Infection of the root system may occur resulting in reduced emergence, damping-off after emergence, or stunting of the crop. Infections at the nodes will often result in a breaking over of the tiller at the infected node. The infected node may have a salmon coloration to it.

    Seed which has been infected may be contaminated by toxins produced by the Fusarium pathogen. There is some indication that the greater the number of pink seeds, the higher the level of toxin. However, grain from infected fields which has very few or no pink seeds may still have high toxin levels. If feeding problems develop contaminated grain may be diluted with uninfected grain to safe levels.

    Control is difficult since the pathogen has a wide host range. Disease severity may be enhanced by humid weather during heading and ripening stages. The use of high quality seed treated with a fungicide, field sanitation, and crop rotation, combined, can reduce disease severities. However, control is only partial.

    10. Snow Mold

    Snow Mold is a disease of winter cereals which occurs when there is adequate snow coverage, but a lack of frost in the soil. These conditions are ideal for several patogens such as Fusarium nivale, Sclerotinia borealis and Typhula spp. which are active at very low temperatures.

    The first indication of disease is observed as a pinkish tinge to the foliage as the snow melts in the spring. This is most characteristic of Fusarium snow mold, while Sclerotinia snow mold can be identified through close observation for small black sclerotia on dead leaves. These sclerotia are masses of mycelium which serve a reproductive function.

    Control of these diseases is difficult. There is little resistance available. Fall rye is frequently more susceptible than winter wheat. Cultural practices such as rotation, field sanitation, and seeding at recommended dates are important.

    11. Smuts

    Smuts, caused by Ustilago spp., are common diseases of barley, wheat, and oats. There are two basic kinds of smuts, covered smut and loose smut. The kind of smut and the host plant they infect will have a direct bearing on the control methods. Smuts cause the most problems where seed from infected fields is used and no appropriate control measures are taken.

    Smuts are easily recognized by the black spore masses which replace the kernels. This is only evident after the heads have emerged from the boot. Loose smutted heads are covered by a very thin and delicate membrane which rapidly ruptures to expose black spore masses. The spores adhere loosely and are easily dislodged and by harvest only a bare spike remains. Spores are usually released at flowering time and dispersed by the wind. In loose smut of wheat or barley, the spores lodge in the flower where they germinate and infect the embryo of the developing seed. At this stage it does not kill the embryo but remains dormant within it. When the infected seed is planted, the fungus grows systemically within the plant and eventually infects the developing heads prior to emergence from the boot.

    In covered smut, the black spore masses are enclosed within a persistent membrane which will usually remain intact until the grain has matured. Once released, spores land on the exterior of healthy seed where they remain dormant. When infested seed is planted, the spores germinate along with the grain. The fungus penetrates the developing seedlings and grows within the plants. Loose smut of oats is similar in that the fungus is carried on the exterior of the seed.

    With smuts, the amount of disease depends largely on the level of smut in the field where the seed was grown during the previous year. The amount of disease can be reduced through the use of resistant cultivars, and or appropriate seed treatment will also significantly reduce the problem. The use of systemic fungicide seed treatments is important in the control of loose smut of barley and wheat. Either systemic or non-fungicide seed treatments can be used to control loose smut of oats and covered smuts of barley and oats. The continued use of non-resident or untreated seed in successive years will result in a substantial increase in smut every year and will result in substantial yield losses.

    12. Ergot

    Ergot, as caused by Claviceps purpurea, is a fungal disease primarily found on rye. However it can also be a problem on barley, wheat, and many other cultivated and wild grasses.

    This disease is characterized late in the season by the presence of hard, curved, and elongated purpleblack ergot bodies. These ergot bodies completely replace the kernel and are usually several times the size of a normal seed. Ergot bodies may be harvested with the grain or fall onto the soil. When sown with seed or left on the soil surface, the ergot bodies will develop spore bearing organs which disseminate spores in splashing rain or wind. If these spores land on the flower stigma, they will infect the ovary of the developing flower. Spores develop in a sugary slime called honeydew which exudes from the infection. The honeydew attracts flies which in turn carry the spores to other florets.

    Ergot is favored by cool, wet weather because it prolongs the period of flowering. Susceptibility to infection is greatest just prior to flowering, decreasing thereafter.

    The presence of a high percentage of ergot bodies in feed grain should be avoided, since they contain toxic materials which are harmful to the circulatory system of animals. Large single doses or continuous small dosages cause the contraction of blood vessels which can lead to reduced circulation, breakdown of tissue particularly in the extremities, abortion, reduced lactation, and even death. If feed is contaminated by ergot bodies, in excess of 0.1% ergot bodies by weight, it must be properly cleaned prior to use.

    Ergot bodies act as the source of inoculum for the next season; therefore, crop rotation and field sanitation are important. Infected weed grasses can act as a primary source of inoculum and should be cut or eliminated from within and around the field. Grain containing ergot bodies should be cleaned prior to use. If ergot bodies are present in the seed, it can be successfully used for planting if the seed germination is high and it is at least twelve months old, but it should not be used as feed.

    13. Barley Yellow Dwarf Virus (BYDV)

    This is a virus disease which is common to barley, wheat, oats, and other cultivated and weed grasses. Transmission of the virus from plant to plant is dependent on aphids.

    Symptoms of BYDV are somewhat similar on the different cereals, but, each exhibits a characteristic color difference. In barley, evidence of infection begins as yellowing which progresses from the leaf tip down towards the base of the leaf. In oats, BYDV is often referred to as Red Leaf. The discoloration is of a reddish color and follows the same pattern as in barley. Infected wheat leaves usually have a purplish coloration.

    Symptoms of BYDV will often appear at the margin of fields or as patches within the field. These patches serve as centers for future spread. Aphids may be carried by the wind and the virus is thus spread over long distances. It will usually take two to three weeks after aphids carrying the virus feed for disease symptoms to first appear. Care must be taken not to confuse BYDV with fertilizer deficiencies, root rots, or low temperature effects.

    Early infections result in extensive leaf discoloration, severe stunting, and in some cases heads may not form. Late infections result in less discoloration and stunting, and small heads that may be partially or entirely sterile. Large yield losses are a possibility, the level of which will be dependent on when the plant is infected. Fall infections of winter wheat may also predispose the plants to greater winterkilling.

    BYDV is transmitted solely by feeding aphids which acquire the virus from perennial grasses or diseased winter cereals. Early infections may originate from aphids blown up from southerly areas where cereal crops are in a more advanced stage of growth.

    Barley and wheat varieties are usually less susceptible to BYDV than oats. Late seeding of spring cereals and early-seeding of winter cereals should be avoided so as to prevent a heavy build-up of aphid populations at critical periods in the plant development. Use of good quality seed and adequate soil fertility results in increased plant vigor which reduces the damage caused by BYDV. The use of insecticides for aphid control may be effective but often difficult to time correctly. Herbicides can be employed to control alternate hosts which act as reservoirs for BYDV between seasons.

    INSECTS

    1. Aphids

    Aphids are very small soft green insects which feed on cereals and many other types of plants and can cause considerable damage. The cereal aphids feed by sucking plant juices which may reduce yield by directly weakening the plant. Probably of greater importance, however, is that they may also transmit the virus responsible for barley yellow dwarf (BYDV). The destructiveness of aphids is dependent on a number of factors, including weather conditions, number of aphids, insect predators such as the lady beetle larvae, and whether or not the aphids are carrying the virus, BYDV.

    The best control for aphids and associated virus disease is to plant spring and fall grains at optimum times so that the crop is well advanced when the aphids become prevalent. Host plants will therefore suffer relatively less feeding and virus damage. Insecticides can be used to control the aphids but timing is very important. The insecticides should be applied before aphids develop wing pads which indicate they are about to migrate. If numerous lady bud larvae are noted, then chemical control is not warranted as lady bug larvae are predators on aphids. For further information, see the section on Barley Yellow Dwarf Virus.

    2. Wireworm

    These insects are reddish-brown segmented worms approximately 3 cm long and 2 mm wide. Extensive damage often occurs to cereal crops which follow sod crops. Seedling emergence can be poor and stands patchy because of the worms chewing the young seedling just below the soil line.

    Control is best achieved by the use of a dual purpose seed treatment which contains both an insecticide and fungicide which provides seedling protection from both insects and fungal pathogens.

    3. Armyworm

    Armyworms, Pseudaletia unipunate, are insects which periodically occur in various parts of the Atlantic Region. These insects can be very destructive if not controlled as they stripe off the leaves and heads leaving only the stems. They migrate from field to field as food sources become scarce. The larvae are about 5 cm. Iong, dark green to brown with white stripes along the sides and back.

    These insects should be controlled at outbreak using recommended insecticide sprays.

    4. Jointworm

    The insect, Tetramesa hordei, is only found on Prince Edward Island, in localized areas, where heavy losses have been reported. It is a tiny fly lays eggs in the stems of barley plants. The eggs hatch, producing larvae which cause galls and distortions of the stem preventing proper head development. Susceptibility to lodging is also increased.

    NON INFECTIOUS DISORDERS

    1. Nutrient Disorders and pH Effects

    Cereal crops remove nutrients from the soil through growth and reproduction. If essential nutrients are deficient for the plant's requirements, poor growth and low seed production results. Nitrogen (N), potassium (K), and phosphorous (P) are required in large amounts. Several other nutrients are also required, but in lesser amounts. Availability at the various nutrient elements may be interrelated and affected by moisture, temperature, soil pH, and related factors.

    Cereal crops grow best when the pH is 6.0 or above. Soil pH below this level will influence the plant's ability to take up nutrients in proper portions to maintain a satisfactory rate of growth. Fields in the Atlantic Region which have not been limed recently may have a soil pH as low as 5. Barley is more sensitive to low soil pH than either oats or wheat. However some barley varieties are more tolerant than others to low soil pH.

    Nutrient deficiencies, including those associated with incorrect soil pH, may often be recognized by abnormal coloration of the plants. Nitrogen deficiencies show up as a yellowing accompanied by slow growth of the crop. Symptoms of other nutrient deficiencies vary widely depending on which nutrient(s) is limiting. Proper identification often requires chemical analysis of the soil and plant tissue to determine the levels of nutrients available.

    Nutrient related problems can be corrected either by adjustments to the soil pH, to ensure that the nutrients are available to the plant, and through the addition of fertilizers to the soil. Soil pH may be

    adjusted through the addition of lime. A time period of several months is required for the lime to increase the soil's pH. Properly taken soil samples are essential in determining correct fertilizer and lime requirements. For further information see "Soil Fertility Guide Publication 535-81".

     


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