Collect and destroy all leaves in the fall, including those from nearby flowering crabapples.
Cedar apple rust. The spores that infect apple trees come from galls produced by the fungus on cedars (junipers). Where cedar apple rust is a problem, do not plant susceptible apple varieties near red cedars (junipers). Where cedars are part of an established landscape, remove and destroy all galls caused by the rust fungus on cedars in the late fall. Inspect the cedars again in the early spring during or just after a rain when the orange, gelatinous fungus growth from any remaining galls is highly visible, and remove them.
Powdery mildew and summer rots. Prune out and destroy all dead or diseased shoots and limbs while the trees are still dormant. Mid-March is usually a good time to prune trees. All pruning cuts should be made at the base of the branch leaving only the branch collar (1/4 to 1/2 inch) so that proper healing of the wound occurs. As a rule, tree wound paints and dressing should not be used at the time of pruning.
Apple maggot, codling moth and plum curculio. Fruits on the tree showing entrance or exit wounds (holes) of either the apple maggot or codling moth should be removed and destroyed immediately. Similarly, all fruits that fall prematurely, especially during May and June, should be promptly collected and destroyed. This is an important step because it prevents developing larvae from reaching maturity and causing more damage to other fruits later in the season.
Create an Environment Unfavorable for Diseases
Apple and pear scab, powdery mildew and black rot diseases are more serious in moist, shaded locations. These diseases can be reduced by improving air movement through and sunlight penetration into the tree. Prune away overhanging vegetation from nearby landscape trees. Thin fruit trees to promote greater sunlight penetration. If watering is needed, irrigate the soil around the trees rather than using overhead sprinklers, so long periods of leaf wetness are avoided. Plant new trees in well-drained sunny locations. If soil is constantly wet, improve soil drainage by ditching and tilling.
Exclude Diseases from the Home Fruit Planting
Some diseases, especially soilborne and root diseases, may be brought into the planting on transplants. Buy nursery stock only from reputable growers. Inspect all purchases for galls, root decay, stem cankers or insect pests and exclude diseased plants from the home fruit planting.
Use Disease-Resistant Cultivars
Several apple cultivars are resistant to apple scab and have varying levels of resistance to other diseases such as powdery mildew, rusts and fire blight (see Tables 9 and 10).
Banding to Control Codling Moth
Fully grown codling moth larvae are attracted to corrugated cardboard cut into six-inch strips, as a place to pupate; the strips can be removed and destroyed to prevent codling moths from reaching adulthood. Corrugated strips attached to the tree in early June can be removed and destroyed in mid-July for first generation codling moth; new strips attached in early August can be removed and destroyed in winter for second generation codling moth.
Bagging fruit
Paper bags can be placed over individual fruit early in
the season to protect them from codling moth, apple maggot,
and flyspeck. Special 2-layered fruit bags made in Japan,
or ordinary paper bags and twist ties can be used. Fruit
should be bagged when they are 1/2 to 3/4 inch in diameter,
which is usually about 3 weeks after petal fall. Bags should
be removed 2 to 3 weeks before harvest to allow normal
color development. A trial in Ohio showed that 41% of
unbagged untreated apples were damaged by codling moth, while
only 19% of bagged fruit were damaged by codling moth.
For more information, see the fact sheet on fruit bagging from
the University of Kentucky, available via the internet at:
http://www.uky.edu/Ag/Entomology/entfacts/fruit/ef218.htm
Insect Traps
Traps can be used to control or monitor some pests of apple and pears. Traps usually catch the adult form of insects that cause damage in their immature form. For more information, see NCR Extension Publication 359, Insect Traps for Home Fruit Insect Control.
Apple maggot infestations can be effectively prevented by sticky red ball traps that attract the adult female apple maggot flies before they lay their eggs on apple fruit, if used at a rate of 1 ball trap per 100 apple fruits. Maggot traps should be placed in trees from mid-June until mid-August.
Codling moth can not be controlled by traps, but the codling moth population can be monitored by traps so that the best time for an insecticide spray can be determined. The codling moth trap uses a sex pheromone lure that attracts only male codling moths. The lure should be placed in a sticky cardboard trap or a bucket-style trap. The trap should be set up at bloom. The best time to spray insecticide for codling moth control is when eggs are hatching. A rough rule for the best time to spray is about two weeks after the first moth is trapped or one week after peak catch. A more refined rule is to calculate degree days (base 50F) after sustained trap catch begins, and spray after 250 degree days have accumulated. Each day, the number of degree days is the average temperature minus the base temperature. For a base of 50F, daily degree days = [(maximum temperature + minimum temperature) / 2 ] - 50.
When to do these practices
A calendar that shows the most appropriate time for the cultural and mechanical practices mentioned here is shown in Table 8 on page 16.
Special Problems on Pome Fruit Trees Fire Blight on Apples and Pears
Fire blight, like most plant diseases caused by bacteria, is hard to control, but can be greatly reduced by planting the more resistant cultivars (see Table 9) and using good sanitary practices. Although fire blight occurs on most cultivars of apple and pear, it is most destructive to Jonathan, Lodi, Gala, Rome Beauty, Wealthy, Transparent, and Idared apples and Bartlett, Clapp Favorite, and Bosc pears. Fire blight is generally a serious problem on most of the more desirable pear cultivars. Bartlett pears are very susceptible to fire blight. Pear cultivars that are resistant to fire blight include Magness, Maxine and Honeysweet.
Sanitation methods for fire blight consist of thoroughly examining the trees at least once a week from the time blossoms appear in the spring until late June, and immediately removing all blighted twigs, spurs, etc. Break or cut infected parts off 8 to 10 inches below the lowest point of visible infection. If removal is made by cuts, avoid spreading the bacteria. Disinfect the blades of the cutting tools by dipping them in 10 percent household bleach solution or rubbing alcohol between each cut. Before moving on to something else, remove and destroy the diseased material from the vicinity of the trees.
Use nitrogen fertilizers sparingly around pears and susceptible apple cultivars. Too much nitrogen causes excessive succulent growth that is very susceptible to fire blight. Terminal growth on susceptible cultivars should not exceed 12 inches per year.
Pear Psylla on Pears
At the green tip stage of pear bud development, tiny pear psylla nymphs appear and begin sucking plant juices. They collect beneath the leaves and if left unchecked, their feeding in summer causes the leaves to turn brown and even drop. Leaves, twigs and fruits are often covered with sticky honeydew (psylla droppings) on which a black, sooty mold grows.
If pear psylla has been a problem, apply a dormant oil spray before buds open, followed by an insecticide at petal-fall. Wait 30 days and if psyllids are still present, make two more applications of insecticide seven to 10 days apart.
Mites
European red mite and two-spotted spider mite can be serious pests of apple leaves, especially after frequent insecticide sprays have killed their natural enemies. Where spider mites are a problem, the best control strategy is to use several tactics. First, a thorough spray of horticultural oil at the green tip bud stage in early spring will reduce the overwintering population. Second, use insecticides only when most needed, to encourage survival of natural enemy insects that feed on mites. Third, select insecticides that have at least some mite activity, such as diazinon, malathion, or rotenone. Fourth, use insecticidal soap either alone or mixed with any insecticides to be applied for control of pest insects. Finally, when the number of mites per leaf averages six to ten, apply Kelthane (dicofol) miticide and repeat in 5 to 7 days. Two treatments are needed because Kelthane does not kill eggs, and eggs hatching within the first few days after treatment can quickly lead to a buildup of large populations. The miticide treatments may not be necessary every year, but when they are, be sure to use the two-spray treatment.
Pesticide Spray Program
A preventive approach emphasizing early-season control of all major diseases and a number of important insect pests is recommended. The critical time period is between bud break (green tip) and about one week after petal fall. This is the only time that certain diseases (scab, apple rust and powdery mildew) and insect pests (scales, some aphids and plant bugs) can be controlled effectively. In other cases (scab, pear leaf spot, mites, plum curculio, pear psylla and leafrollers), a good early-season program not only provides excellent control, but also greatly reduces the potential for late-season damage and, therefore, the need for frequent sprays later in the season. Where an early-season control program is followed, the timing of mid- to late-season sprays is much less critical and the interval between applications often can be safely lengthened to as much as two or three weeks. Suggested spray schedules are listed in Table 11.