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Dormant sprays kill fungal diseases on plants, fruit and nut trees

A dormant plum tree.
A dormant plum tree.

Q: I just moved into a home that has several fruit trees. My neighbor said I need to dormant spray. What is this and why should I do this?

Katie L. Atascadero

A: Dormant sprays — horticultural oils that include some insecticides and fungicides — are applied when plants and trees are in their dormant stage, after all leaves have fallen.

These sprays kill fungal diseases that are hidden beneath the bark and within cracks and crevices of your plants or fruit and nut trees. The sprays can also suffocate overwintering insects and eggs on a plant.

Dormant sprays are usually combined with an oil for easy application and can be applied in late fall, winter and early spring. Winter and early spring applications should occur before the trees form flowering buds. Spraying when flowering buds are present can disrupt bees and other pollinating insects, resulting in little or no fruit.

Copper and sulfur sprays are used in combination to control a variety of diseases including leaf blight, shot hole and peach leaf curl.

Dormant sprays are the least disruptive to beneficial insects and the environment when they are applied properly. It may be necessary to use the sprays several times for diseases with a long infection period, such as fire blight.

Water trees well before applying the spray to prevent burning plant tissue. Choose a windless day when the temperature can remain above 50 degrees for at least 24 hours. Be careful of spray drift because it can harm evergreen plants, trees and annual flowers.

If you have a fish pond, spray drift can also harm fish. Apply thoroughly to coat the entire surface of the plant or tree. The spray is not effective once it dries.

Fungal spores and some insect pests can overwinter among the fallen leaves. As a result, it is important to rake and dispose of leaves to minimize the harboring of pests and diseases that can cause damage the following season.

Dormant sprays used at the right time and in the correct way can be one of the most satisfying tasks you perform in your garden to maximize flower and fruit production and enhance your garden’s productivity.

Leonard Cicerello is a UCCE Master Gardener.

Got a gardening question?

In San Luis Obispo call 781-5939, Arroyo Grande, 473-7190 and Templeton, 434-4105. Visit us at http://ucanr.org/sites/mgslo/ or email us at anrmgslo@ucanr.edu. Follow us on Instagram at slo_mgs and like us on Facebook. Informative garden workshops are held the third Saturday of every month, 10 a.m. to noon at 2156 Sierra Way, San Luis Obispo. Garden docents are available after the workshop until 1 p.m. To request a tour of the garden, call 781-5939.