Spray your deciduous fruit trees now to protect them from pests

After a few years of watching and waiting for a peach tree I planted to bear fruit, he finally did this year. Unfortunately, he was unable to produce in those early years due to peach leaf curl, a fungal disease.

The peach, apple, pear and many other types of deciduous fruit trees are vulnerable to diseases and insects that can impact agricultural production and ultimately the health of the tree. . Applying dormant oils can help protect trees from soft-bodied insects and leaf curl, bullet hole fungi, powdery mildew and other fungi.

Photo by Karen Gideon

Deciduous fruit trees are vulnerable to diseases and insects like aphids.

Dormant oil sprays (for example, horticultural, narrow-scope, or premium oils) are non-chemical pesticides. These highly refined petroleum products or vegetable oils (soy, cotton, sesame, neem or other oils) are mixed with water and applied to trees and shrubs during the winter when the trees are dormant. Applied at the point of runoff on the branches and trunks of fruit trees, these sprays clog the pores through which insects like aphids, spider mites, psyllids, thrips and mealybugs breathe, thus suffocating them. Thorough application and coverage is essential, as many insects prefer the underside of leaves or reside below sepals or buds where they are difficult to reach.

Wear protective gear, long sleeves and long pants when spraying. Be careful not to swallow, inhale, or expose your skin and eyes to the oil.

The right timing is essential. Dormancy oils should be applied at the onset of dormancy in late November and again during leaf bud swelling just before buds begin to open in February or early March. Associating the timing of the spray with Thanksgiving and Valentine’s Day can be helpful in stimulating the mind. The timing coincides with the increasing activity of wintering insect larvae.

These oils are temperature sensitive, so apply on a clear, windless day in the 50-70 degree temperature range when the temperature should not drop to freezing for 24 hours after application.

A good time to apply dormant oil is right after a period of rain or fog. Do not apply to drought stressed trees or to any tree during foggy, rainy weather or during or before hot or freezing weather. If it rains within hours of application, reapply the treatment. Do not apply within 30 days of or after applications of sulfur or certain other fungicides to avoid damage to trees.

Dormant oil applications are not appropriate on citrus or avocado trees because these species do not go into winter dormancy.

When mixing spray solutions, mix less than you think you need, as removing leftovers is difficult. Estimate how much your trees will need for good coverage by performing a water spray test. Always follow the directions on the container label. Although horticultural or dormant oils leave no residue, so they have limited impact on pets, wildlife and beneficial insects, they are toxic to fish. Carefully follow the precautions listed for protecting bees by spraying only early in the morning or late at night.

In addition to the use of dormancy sprays, there are several other important non-chemical cultural management options. Avoid sprinkler irrigation; plant fruit trees in full sun. Rake and destroy (do not compost) fallen leaves around your fruit tree – space tree plantings and prune to ensure good air circulation and light penetration.

Incorporating good cultural practices into your garden maintenance program will pave the way for more effective pest control. By applying dormant oils annually as directed to well-maintained fruit trees, you will help protect your trees from several overwintering insects and prevent damage to flower and leaf tissue.

Most actively growing plants are not adversely affected by horticultural oils, especially if they are not under environmental stress. If used correctly, horticultural oils can be a less toxic approach than chemical-based insecticides.

Sponsored by UC Cooperative Extension, the University of California Marin Master Gardeners provides science and science information to home gardeners. Email your questions to [email protected]g. Attach photos for inquiries about pests or plant diseases. The office is closed for walk-in visits. Subscribe to the Leaflet, UC Marin Master Gardener’s free quarterly e-newsletter, at marinmg.ucanr.edu


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