Master Gardener: Winter Control of Deciduous Fruit Tree Pests | Home and garden

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All deciduous fruit trees are susceptible to insect and disease problems affecting fruit quality and tree health. The best time to manage many of these pest and disease issues is during the winter dormancy period, which occurs after the leaves have dropped but before the buds begin to open in the spring.

Key management practices at this time of year include:

• Prune to remove dead, diseased and broken branches, promote vigor, open the canopy to the sun and improve air circulation;

• Sanitation to remove mummified fruit on the tree and wood, diseased fruit and leaves from the ground;

• Apply dormant sprays to control pests, limit infection and prevent the spread of certain diseases.

The absence of leaves in winter provides an unobstructed view of the tree’s framework and the opportunity to thin (completely remove) or top (cut) the branches. Dormant pruning will be less if fruit trees receive proper training and summer pruning. To control pests and diseases, prune all dead, diseased, crossed or broken branches, as well as water shoots and suckers. Remove and destroy all diseased wood.

Sanitation is necessary to prevent disease and pests and reduce the need for sprays. If possible, rake up and dispose of all leaves after they fall and before the first rains. Remove and destroy overwintering fruit (mummies) in the tree and on the ground to eliminate sources of insects and disease the following season.

Dormancy or delayed dormancy sprays

Dormant sprays or delayed dormancy sprays are generic terms for pesticide applications applied when trees are dormant or have just swollen buds. Pesticides include organic or inorganic fungicides, insecticides and pesticidal (horticultural) oils.

Overwintering sprays provide effective and economical treatment for a number of overwintering diseases and pests, such as

• Scales (both armored and soft-shelled) in many species of fruit trees.

• Lesser peach borer in apricot, nectarine and peach, and sometimes plum and plum

• Aphid eggs in many species of fruit trees

• Leaf roll fungus in nectarine and peach

• Shot hole mushroom in apricot, nectarine and peach

The most commonly used fungicide in the home orchard is copper spray, but other synthetic sprays are readily available. Spinosad, a natural product, is considered a biological insecticide and is added to some dormant oil sprays to control more insects like peach tree borer, naval orange worm and oriental fruit moth. Oil sprays refer to “highly refined horticultural oils” including insecticidal oils, narrow range oils, supreme or superior type oils. Follow label precautions regarding tree species and specific timing of tree temperatures, humidity and stress.

Dormant sprays are not always necessary. For some pests and diseases, a single dormant application may be sufficient with good spray coverage. For other problems and depending on pest pressure, up to 3 applications may be required for good control. Decide if and how many applications you need to apply by noting the amount of insect and disease pressure during the previous growing season.

For more information on fruit tree pruning and pest control, download the article: https://anrcatalog.ucanr.edu/pdf/8368.pdf. There are general recommendations for types of fruit trees and a list of useful references.

The following link will take you to the UC IPM fruit and nut page. http://www.ipm.ucdavis.edu/PMG/GARDEN/fruit.html. Choose the type of fruit tree in your garden and you are well on your way to accessing the information. There is also cultural information that offers advice on how to prune very young and mature fruit trees.

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