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Apple

Malus spp. (Rosaceae)

Apples are deciduous trees growing from 6' to more than 30', depending on soil, rootstock, and cultivar. The showy, pink-tinged white blossoms appear in spring mostly on spurs--short branches that elongate only a fraction of an inch per year. Apples are hardy in Zones 3-9.

Culture

Plant in full sun in well-drained, moderately fertile, slightly acidic soil. Train trees to a framework of well-spaced, wide-angled branches. Prune bearing trees each winter to admit light into the tree and encourage good air circulation. As you prune, remove diseased and spindly wood and crossed branches. Where dense growth blocks out light, remove extra shoots at their bases. To develop growth on spindly shoots, remove the end of the shoot just above an outward-facing bud. For more pruning information, see "Pruning and Training" on page 101. For best results, choose cultivars resistant to a wide range of diseases. These include 'Jonafree','Liberty','Nova Easy Grow', 'Priscilla', 'Redfree', and 'William's Pride'.

To set fruit, most cultivars need cross-pollination by a second compatible apple or crab apple planted within 40'-50'. Some cultivars, such as 'Jonagold' and 'Mutsu', produce nonviable pollen and can't serve as pollinators. A few, like 'Golden Delicious', are self-pollinating. If you're planting 1 tree, improve fruit set by grafting a branch of a suitable pollinator onto the tree.

Fruit Problems

Fruit with holes surrounded by brown, crumbly excrement. Cause: Codling moths. Adult codling moths appear in early spring and lay eggs in trees within 2-6 weeks of blossom time. Eggs hatch into larvae within 5-14 days. The fat, white or pinkish, 7/8" caterpillars tunnel through fruit and may have departed by the time you discover the holes, which may be filled with what looks like moist sawdust. For light infestations, kill eggs by spraying superior oil on leaves and twigs within 2-6 weeks of blossoming. For heavy infestations, kill larvae before they tunnel into fruit by spraying the tree canopy with Mania at petal fall and again 1~14 days later. Pyrethrin spray mixed with a synergist also kills larvae. For additional details on codling moth's life cycle and controls,

Codling moths often produce several generations per growing season. Trapping the pupating caterpillars aids control. Remove loose bark and wrap the trunk with a band of corrugated cardboard or burlap. Periodically remove the band and destroy pupae. Also inspect harvest containers for pupae.

Since codling moths prefer crowded fruit, you can discourage attack by thinning apples until no fruit touches. Infested apples may drop early; pick up and destroy dropped fruit before larvae emerge to pupate. If you have a single backyard tree and no other trees in your area, try trapping male moths with pheromones. Mating disruption pheromones are also available. Since females rarely fly more than 100 yards looking for host plants, plant your trees well away from other apple, pear, or walnut host trees in your area.

The effectiveness of other controls depends on local conditions. Introduced Trichogramma wasps control this pest in some orchards but not in others. Success depends on such factors as weather, optimum timing of parasite release, and using the correct species of wasp. If you'd like to try this technique, be sure to purchase a species of Trichogramma that parasitizes codling moths. BTK may also help with control, but you have to apply it during the 3-5 days between the time when the eggs hatch and the larvae enter the fruit. Once the larvae are in the fruit, BTK is ineffective. You may find that BTK is more effective when combined with a feeding attractant (also called an appetite stimulant), such as molasses. See the opposite page for an illustration of this pest.

In the future, gardeners may be able to buy new experimental codling moth control products, such as codling moth granulosis virus. Another experimental product, encapsulated BTK, releases the bacteria through a timed release capsule for potential long-term control of codling moth larvae. Also, cultivars resistant to codling moths may eventually be available.

Fruit dimpled; brown tunnels through flesh. Cause: Apple maggots. These 1/4" larvae of the apple maggot fly ruin fruit by copious tunneling. Adult flies emerge from soilborne pupae in late June and continue to appear until early autumn. Flies puncture fruit skin and deposit eggs, which hatch into fruit-tunneling maggots. Infested apples often drop. To prevent buildup of pupae around trees, collect and destroy dropped fruit at least weekly.

Apple maggot flies are attracted to fruit by sight. You can control them by trapping them on dark red balls coated with a sticky coating, such as Tangle-Trap. Buy commercially made traps or make your own from discarded croquet balls. In mid-June hang 1 trap per dwarf tree or 4-8 traps per full-size tree. Hang traps at eye-level, 2'-3' in from branch tips, near fruit but not completely hidden by leaves. Clean traps every few days and reapply the sticky coating. See page 23 for an illustration of this pest.

Young fruit with crescent-shaped scars. Cause: Plum curculios. This beetle, common east of the Rocky Mountains, leaves a characteristic crescent-shaped scar as it lays eggs in fruit. Damaged apples may drop, but frequently will remain on the tree. Since plum curculios cannot mature in hard apple flesh, fruit that doesn't drop will be superficially scarred but otherwise edible.

To control this pest without sprays, spread a dropcloth beneath the tree and jar the trunk and branches with a padded mallet. Collect and destroy curculios that fall onto the sheet. For best results, jar the tree twice a day, beginning as soon as you see the first scarred fruit. In addition, prevent hatching of some curculio eggs by picking up and discarding dropped fruit. Some apples ('Mutsu', for example) are more resistant to plum curculios than others. In the future, breeders may be able to develop other apple cultivars with even greater curculio resistance.

Fruit with brown, velvety or corky surface lesions. Cause: Apple scab. This serious, widespread disease begins when spring warmth and moisture promote the discharge of fungal spores from old, infested apple leaves into the air. These spores can infect the leaves and fruits of susceptible apples growing nearby. To prevent scab from spreading into the tree each spring, destroy dropped leaves in the fall. Either collect and compost leaves in a hot compost pile or hasten their decay on the ground by shredding them with a lawn mower. You may also till leaves into the soil or spray them with a nitrogen source, such as blood meal, to speed decomposition.

Growing-season applications of copper, sulfur, or lime-sulfur sprays will help control scab. If you have susceptible cultivars or if the weather is very warm and wet, spray weekly beginning with the appearance of the first green tips on the tree until disease pressure subsides. Pruning to encourage sunlight penetration and air circulation also helps with control. Scab-resistant cultivars include 'Golden Delicious', 'Grimes Golden', 'Jonagold', 'Jonathon', 'Mutsu', 'Spigold', and 'York'.

In the future gardeners may be able to treat fallen leaves with a fungus such as Athelia bambacina, which inhibits development of overwintering apple scab. See page 23 for an illustration of apple scab.

Fruit with rotting spots. Cause: Summer disease. Summer diseases are fungal diseases associated with hot weather. Dark spots with alternating black and brown rings indicate black rot. Other summer diseases include bitter rot (slightly sunken, tan spots) and white rot (watery decay). Black rot prevails where summers are cool; bitter rot and white rot, where summers are warm. Summer disease fungi overwinter in mummified fruit and in cankers on diseased wood. To control, remove and dispose of all cankered wood. Collect and destroy mummified fruit. Black rot and white rot attack weakened or wounded trees, so keep them healthy with good pruning and nutrition. Prune in early spring, when wounds heal most quickly. Sulfur sprays help control black rot (see page 23 for an illustration). Cultivars resistant to bitter rot include 'Akane', 'Blairmont', 'Fuji', 'Hawaii', 'Jonafree', 'Jonalicious', 'Liberty', 'Melrose', 'Priscilla', and 'Spartan'. Cultivars resistant to white rot include 'Akane', 'Arkansas Black', 'Arkansaw', 'Dayton', 'Fuji', 'Hawaii', 'Jonafree', 'Jonalicious', 'Liberty', 'Limbertwig', and 'Melrose'.

Fruit with yellow skin spots that later turn orange. Cause: Cedar-apple rust. Infected fruit is small, deformed, and may fall prematurely. For more information see "Leaves with pale yellow spots that enlarge and turn orange" below. Fruit with surface netting or russeting. Cause: Powdery mildew. For more information, see "Leaves with a light powdery coating" below.

Fruit with red skin spots bearing white centers. Cause: San Jose scale.

Fruit with raised black spots or brown smudges on the surface. Causes: Fly speck; sooty blotch. Black spots are fly speck; brown smudges are sooty blotch. Both of these blemishes are fungal diseases and both can be controlled with sulfur sprays. But since both are superficial, you can just rub them off the fruit.

Leaf and Branch Problems

Leaves with olive-brown, velvety spots that become brown and corky. Cause: Apple scab. Infected leaves may turn yellow and drop prematurely, further weakening the tree. For more information see "Fruit with brown, velvety or corky surface lesions" above.

New leaves twisted or curled and covered with a sticky coating. Cause: Aphids. You may find these tiny green, black, gray, pink, or white fluffy-coated insects on leaf undersides. The leaves may be covered with a black coating, caused by a fungus called sooty mold that feeds on the honeydew exuded by aphids. Aphids weaken trees by sucking sap, but they depart by midsummer. For a light infestation, just wait it out. Also grow nectar-producing flowers, such as dill and buckwheat, near your trees to provide food for aphid predators (parasitic wasps, lady beetles, and hover flies). Or attract aphid predators by spraying commercial or homemade yeast-and-sugar mixtures on your trees.

Leaves with pale yellow spots that enlarge and turn orange. Cause: Cedar-apple rust. Leaves infected with cedar-apple rust may drop prematurely. This fungal disease overwinters as a gall on various juniper species--commonly on Eastern red cedar (Juniperus virginiana). In the spring the galls, swell, push out orange horns, and discharge disease spores that are borne on the wind to infect apple trees. The leaf spots caused by cedar-apple rust won't spread disease into the tree, and you can't make them go away once they appear.

Cedar-apple rust isn't a problem in areas with few Eastern red cedars or other junipers (Juniperus spp.). Removing nearby Eastern red cedars won't prevent the arrival of windborne disease coming from trees miles away. Sulfur sprays are only fairly effective. Resistant cultivars include 'Arkansas Black', 'Empire', 'Gala', 'Granny Smith', 'Gravenstein','Grimes Golden', 'Jerseymac', 'McIntosh', 'Macoun', 'Tydeman's Red', and 'Winesap'.

Leaves with a light powdery coating. Cause: Powdery mildew. As this fungal disease becomes more severe, leaves may curl lengthwise and drop. Since it overwinters in dormant buds, winter pruning of infected buds, which show white fungal growths, aids control. Spray sulfur for growing-season control. Resistant cultivars include 'Empire', 'Golden Delicious', 'McIntosh', 'Mutsu', 'Red Delicious', 'Rhode Island Greening', and 'Spigold'.

Leaves suddenly blacken, with tips of growing shoots bent over. Cause: Fire blight. Don't confuse this disease with sooty mold, a black fungus that rubs off easily. Fire blight bacteria may travel to roots and kill the entire tree. For growing-season control, remove blighted parts at least 6" below the infected area. Between cuts, dip tools into isopropyl alcohol or 10 percent bleach solution (1 part bleach to 9 parts water). Resistant cultivars include 'Arkansas Black', 'Baldwin', 'Ben Davis', 'Empire', and 'Winesap'.

Whole Plant Problems

Leaves yellow; death of whole branches. Cause: San Jose scale. Clusters of these sucking insects cling to bark and appear as small gray bumps that can be easily scraped off with a fingernail. Control with late winter application of dormant oil spray. See page 23 for an illustration of this pest.

Fruit disappears; bark gnawed. Causes: Deer; rabbits; mice.

Tree declines; sawdustlike material on trunk near ground level. Cause: Roundheaded apple tree borers. These creamy white, darkheaded larvae bore into trunks near ground level, girdling the tree or tunneling into the heartwood. Kill borers by inserting a thin, flexible wire or by injecting parasitic nematodes into the hole.

Copyright 1992


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