Pests, Disease, and Dormant Spraying

By Kim McCue   UCCE Master Gardener

What exactly is a dormant spray and how is it used?  Nancy N., Creston 

Generally speaking a dormant spray is any pesticide, including fungicides, highly refined horticultural oils, (often called insecticidal or narrow range oils), or oils in combination with pesticides, which are applied during a plant's dormant period.  Depending on the type of spray being used, the application period ranges from the onset of dormancy all the way into the appearance of bud swell. 

Dormant sprays are ideally used as one piece of an integrated pest management (IPM) program in the home landscape and fruit orchard.  They help reduce populations of certain over-wintering insect pests, such as scale, mites, aphids, and some borers.  Dormant sprays are also effective in limiting infection and spread of bacterial and fungal diseases, such as leaf curl, shot hole, brown rot, fire blight, and powdery mildew. 

In our area, dormancy typically occurs in December and January and is signified by the total loss of leaves on deciduous trees and shrubs. Some sprays can be applied in late November if leaves are already gone.  One reason to spray post leaf drop is to maximize coverage on bark and small branches that are otherwise blocked by leaves. Complete any necessary pruning prior to applying spray to avoid wasting material, which can be costly, on leaves and branches that will eventually be pruned and removed with other garden debris. 

Taking a proactive approach to pest management with dormant sprays during winter, before insects hatch in the spring, helps reduce the use of more toxic pesticides that are sometimes necessary to combat an infestation later in the year.  Plus, the timing of the application and the type of pesticide used makes dormant sprays less disruptive to the life cycles of beneficial insects, making them more environmentally friendly than some other, more toxic pesticides used during the growing season.

Again, dormant sprays are used as part of an IPM approach to garden health.

Source:ucanr.edu