Dormant Spraying Time

By Bob Chapman

In winter-time many animals hibernate, waiting for the warmth of spring to revive, raise their young, gorge on food to fatten themselves up for the coming winter. The insects in our gardens, shrubs and trees don't do all the things that animals do, but the adults do hide in the bark and crotches of plants when the days are short and the weather cool. Some are in pupation  and some have laid eggs that will hatch and attack our plants the next growing season. We spray selected plants when they are dormant to help control harmful insect populations. Spraying dormant plants also helps lessen the number of troublesome insects that can harm our plants in the following growing season.

Insects are not the only thing that we try to eradicate. There are a multitude of fungi that live in or on our plants and we can help eradicate these obnoxious organisms in winter.

We can control over-wintering insects and their eggs as well as controlling many fungi using "Earth Friendly" pesticides.

Common insects that we want to control
Of the millions of insects in the world, only a few attack our plants. Here's a brief list of them we try to control in the dormant period in our gardens:

• Aphids
• Whiteflies
• Scale
• Mites
• Mealy bugs
• Thrips
• Katydids
• Grasshoppers
• Leafhoppers
• Elm leaf beetles
• Japanese beetles
• Psyllids 

Controlling these insects in winter with an oil spray
There are many names used for the water-miscible (can be mixed with water) highly refined oils that we spray on deciduous trees and deciduous shrubs. Among the common product names are Volck Oil, Horticultural Oil, Superior Type Spray Oil, Ultra-Fine, All Seasons Spray Oil and Sunspray.

Applying an oil spray
Oil kills adult insects and their larva by suffocation. Oil plugs the breathing tubes (called spiracles) causing a quick death. The oil must make contact with the insect and be enough to be effective. You can use a pressure tank sprayer or a hose-end applicator for applying horticultural oils. When spraying deciduous trees, fruit trees and deciduous shrubs you must make sure that the oil gets into the many cracks and crevices of the bark and the crotches of the trees. These excellent hiding places give shelter to over-wintering insects and you want the oil to contact them. Carefully read and follow directions on the container for amounts to use and time(s) of application.

Common fungal diseases controlled in the dormant season

• Peach leaf curl
• Black spot on roses
• Powdery mildews
• Rusts
• Molds: gray, blue, white
• Shothole fungus
• Scab
• Fusarium wilt or blight
• Smuts
• Leaf spot

Fungicides for controlling fungal diseases
Fungal diseases produce spores as a means of furthering the species. During the dormant season these spores are found on the bark, its crevices and folds, on deciduous shrubs and trees and on the detritus left from fallen leaves. In the spring these spores are spread to our plants by winds, breezes and splashing water, either from the rain or irrigation.

Our ancestral gardeners or farmers found that powdered sulfur was an effective control for fungal infections. Some added lime and many early gardeners swore by the use of a lime-sulfur spray or dust to control fungal diseases. More recently, copper sprays have been introduced to control fungal infections. Using these "Earth Friendly" fungicides during the dormant period can help reduce the prevalence of fungal diseases next growing season by preventing the current growth and the production of spores.

Products that can be used during the dormant season for controlling fungus include Sulfur Dust and Polysul (calcium polysulfide or lime-sulfur) and Kop-R-Spray.

Summary
Spraying during the dormant season helps control many over-wintering insects and their eggs and helps rid our gardens and trees of fungal infections.

Always read and follow the directions on the container for proper usage of these insecticides and fungicides.

Bob Chapman is a well-known professional gardener and landscape contractor. Currently retired, Bob now spends his time contributing many free-lance garden articles and columns, and is a much sought after lecturer and horticultural consultant.

Since 1987, Bob has appeared as a regular columnist for the San Jose Mercury News. Besides the Mercury, his writings have appeared in the San Diego Tribune, Sacramento Bee, Fresno Bee and the Times Newspaper Group. He is the 1991 winner of the Quill and Trowel Award of the Garden Writers Association of America for the best newspaper gardening article in North America.

Bob majored in Ornamental Horticulture at Cal-Poly, San Luis Obispo. He also served as a member of the Professional Gardeners Association.