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by R. Hammon and D. Davidson* (5/16)

Quick Facts…

• Peaches, plums, cherries and apricots are all stone fruits that can be grown in the lower altitudes of Colorado. Insects and diseases that affect stone fruits vary with location, year and fruit type.
• Cytospora canker is a fungal disease that damages bark and underlying wood tissue and results in an amber- to brown-colored gum on trunk of branches.
• Peach twig borer and Oriental fruit moth can cause severe twig dieback and damage to fruit if not controlled.
• When dealing with any pest, it is always best to practice integrated pest management (IPM). IPM is a sciencebased, decision-making process that identifies and reduces risks from pests and pest management related strategies.
• It is important to time spraying when bees and other pollinators will not be actively visiting flowers to collect pollen and nectar.

Peaches, plums, cherries and apricots are all stone fruits that can be grown in the lower altitudes of Colorado. Insects and diseases that affect stone fruits vary with location, year and fruit type. Peaches, cherries and plums require a dormant oil spray to control aphids wherever they are grown, and cherries require treatments for western cherry fruit fly where it is present. All stone fruits require treatment for peachtree borer. Cytospora canker is a serious and widespread disease of stone fruits. Other foliar diseases can appear when environmental conditions are right for infection.

Integrated Pest Management (IPM)

When dealing with any pest, it is always best to practice integrated pest management. This is defined by the USDA as: “…A science-based, decision-making process that identifies and reduces risks from pests and pest management related strategies. IPM coordinates the use of pest biology, environmental information, and available technology to prevent unacceptable levels of pest damage by the most economical means, while minimizing risk to people, property, resources, and the environment. IPM provides an effective strategy for managing pests in all arenas from developed agricultural, residential, and public lands to natural and wilderness areas. IPM provides an effective, all encompassing, low-risk approach to protect resources and people from pests.”

Spraying Tree Fruit

Pesticides for use on backyard fruit trees are typically available at garden centers and are sold under many trade names and formulations. Label use instructions are constantly changing. For that reason, products are referred to by active ingredient. Not all products containing a given active ingredient may be labeled for use on all crops. Always read and follow label directions when using any pesticide.

Pesticides should be applied to the entire tree including upper and lower surface of the leaves unless otherwise specified. It is important to keep trees properly pruned to a size that is appropriate for the spray equipment that is used. Peaches and nectarines need to be thinned so the fruits do not touch each other to allow complete spray coverage.

Aphid Control with Dormant Oils

Dormant sprays should be applied in early spring as close to leaf bud break as possible. They can be applied as late as when there is ¼” green showing from leaf buds. Oils work by smothering aphid eggs and immature and adult insects, so complete spray coverage is essential.

Green peach aphid attacks peaches and plums, while black cherry aphid attacks cherries in the early spring. These aphids spend the winter as eggs laid at the base of leaf buds. If allowed to hatch and reproduce, aphid feeding can distort and weaken new growth causing production problems the following year. Once aphids become established and are allowed to distort leaf growth, control is difficult. Dormant oil sprays also help with control of peach twig borer and oriental fruit moth which spend the winter as larvae in protected spots on the bark. Dormant oils can be tank mixed with malathion, permethrin or other labeled residual contact insecticides to improve performance.

Western Cherry Fruit Fly Management

Western cherry fruit fly (WCFF) is now present in most areas of Colorado where cherries are grown. Left uncontrolled, fruit will be infested with maggots, which has a major impact on quality and storage life. WCFF control is typically done with a series of contact residual insecticide applications aimed at adult flies as they land to lay eggs. This requires sprays on a 7-10 day schedule beginning when flies become active, usually as early maturing cherries begin to show color. Yellow sticky traps are often used to determine when adult WCFF begin flying. The spray schedule should begin 7-10 days after the first flies are captured.

Commercial growers have had excellent control with a spinosad- based bait (GF-120, DowAgrosciences). It can be applied to spots on the trunk of the tree where adult flies are attracted and killed. Unfortunately, it is available in only in gallon or larger quantities, but it is the best option for western cherry fruit fly control for those gardeners for whom it is available.

Peach Twig Borer/Oriental Fruit Moth

Peach twig borer (PTB) and oriental fruit moth (OFM) have similar life histories and management is the same for both. OFM is limited in distribution to the area around Palisade, while PTB is found statewide. These insects overwinter as larvae in a silken cocoon on protected areas on the trunk of stone fruit trees. Dormant oils combined with a contact insecticide are effective in controlling this stage. First generation PTB/OFM larvae bore into new twig growth, causing them to wilt and die, referred to as shoot strikes. Larvae of succeeding generations may move to fruit where they chew a small entry hole near the stem end, especially on peaches. If shoot strikes are present in a tree during shoot growth a foliar insecticide may be necessary to control first generation larvae. Monitor developing fruit for injury from second generation and apply an insecticide to the entire tree if it is found.

Peachtree Borer

Peachtree borer, also known as crown borer, life history and control is covered in detail in CSU Fact Sheet 5.566: Peach Tree Borer. Preventative treatments should be with a residual insecticide such as permethrin, or carbaryl aimed at the base of the tree. Two or three treatments are necessary, late June at lower altitude, then again in three weeks until early August. Check stone fruit trees for the peachtree borer as soon as the soil thaws in the spring if the July and August treatments were not made the preceding year.

Pear Slugs

Pear or cherry slugs, actually the larvae of a sawfly which resemble slugs, can defoliate cherries (sweet and tart varieties) in mid to late summer. Repeated annual mid-summer defoliation can weaken trees and larvae should be controlled if present in high numbers. Their biology and management is covered in Fact Sheet 5.560: Pear Slugs.

Cytospora Canker

Cytospora canker is a fungal disease that damages bark and underlying wood tissue and results in an amber- to browncolored gum on trunk or branches. It can be an important disease in back yard stone fruit production. Management to reduce stress, sanitation and timely pruning are important in minimizing the impact of Cytospora. The biology and management of this disease are covered in detail in Fact Sheet 2.953: Cytospora Canker in Tree Fruit Crops.

Protecting Pollinators and Crops

It is important to time spraying when bees and other pollinators will not be actively visiting flowers to collect pollen and nectar. These insects are generally active during the day so spraying early in the morning or in the evening when they are not present will help mitigate any unintended exposure to other non-target species.

References

For additional information, see the following fact sheets:

• 2.800, Backyard Orchard: Apples and Pears.
• 2.914, Coryneum Blight.
• 2.953, Cytospora Canker in Tree Fruit Crops
• 5.560, Pear Slugs.
• 5.566, Peach Tree Borer.
• 5.569, Insect Control: Horticultural Oils.

¹Oriental fruit moth is limited mainly to the Palisade and East Orchard Mesa areas of Mesa County.

*Original publication by C.E. Swift, Colorado State University Extension horticulture agent, Tri River Area, Grand Junction; H.J. Larsen, Extension fruit disease specialist, Orchard Mesa Research Center, Grand Junction; and R.W. Hammon, Extension entomology and agronomy agent, Tri River Area, Grand Junction. Reviewed and Revised by R.W. Hammon Colorado State University, Tri River Area Extension agent (Entomology/Agronomy) & D. Davidson, Boulder County Extension agent (Horticulture) 5/02. Revised 5/16

Colorado State University, U.S. Department of Agriculture and Colorado counties cooperating. Fort Collins, Colorado. Extension programs are available to all without discrimination. No endorsement of products mentioned is intended nor is criticism implied of products not mentioned.

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