Regional Gardening Reports :: National Gardening Association

In the Garden:
Western Mountains and High Plains
March, 2005
Regional Report

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Scale insects have protective armor that makes them difficult to control, but well-timed sprays of horticultural oil can help reduce severe outbreaks.

Dormant Sprays for Safe and Early Pest Control

Landscape problems are often noticed too late, long after pests have infested and damaged plants. But you can prevent future severe outbreaks of some insects and mites by using a dormant spray of horticultural oil.

My grandmother used a dormant spray in the home orchard when the trees and vines were without leaves. Her choice was lime sulfur, and this application was effective in killing overwintering diseases, insects, and their eggs before they had a chance to multiply and reinfest the new growth.

Scouting for Scale
Now is the time to inspect your trees and shrubs for mysterious bumps on the stems and branches, which could be overwintering pests. It just might be that scale insects or disease spores are lurking about. Check those bumps or growths carefully by scraping several with your fingernail. If you see any fluid substance, there's apt to be insects or eggs residing there. Use a 10X hand lens for close inspection, if needed.

Scale insects are difficult to control since they are protected by a layer of armor that inhibits the penetration of most pesticides. Once the mother scale settles down, she attaches herself to the plant tissue and spends the remainder of her life there. But she can produce a batch of eggs beneath this armor-like coating, which protects them from the elements and traditional control methods.

Choosing the Right Oil
With proper timing and application, however, a thin film of horticultural oil can help reduce severe outbreaks of scale. Today's dormant oil sprays are more highly refined than they used to be. Some are classified as "heavy oil" and are designed for use strictly on dormant plants prior to the leaves emerging. Other formulations are lighter-weight oils, suitable for later applications. So timing is of the utmost importance.

Lighter oil sprays, which have a higher degree of purity, are further classified as superior, supreme, or summer oils. In many situations, these lighter oils can be applied both in the dormant stage of a plant's life or after bud break and leaf emergence.

I recommend that you apply these dormant sprays as near as possible to the swelling of the buds or early emergence of the leaves, since insect eggs begin to hatch at that time. This will give the greatest control of most scale, mites, and mealybugs on plants that are susceptible. Always read and observe the label directions prior to application. Happy bug hunting!

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