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Safer strategies for battling summer garden pests.

Looking for environmentally sound pest controls? Ones that are safe but still effective? If so, maybe you should ask your grandparents: their 50-year-old methods look better and better today.

Three old-time insect remedies oils, soaps, and sulfur lost their prominence as new chemicals with residual activity were introduced. But the old remedies have improved since our grandparents used them, and all three are once again in the pest control limelight.

Applied properly, these insecticides can control many of the most troublesome garden insects with little harm to you or the environment. Like any spray, these materials are most effective if you thoroughly cover the plant at the first sign of a pest outbreak. The insects they control, as determined by a consensus of Western entomologists, are listed in the chart on the opposite page. Temperature restrictions will limit the usefulness of these materials in very hot climates.

Horticultural oil: the most underrated pesticide

Oils have a long history of garden use, First were the heavy-duty weed oils, which could knock out the toughest weeds. Next came more refined dormant oils, which are still widely used to smother overwintering insects and their eggs on deciduous plants. Finally, superior oils (referred to here as summer oils) arrived, products so refined they can be sprayed on most plants in midsummer without damaging foliage.

Perhaps people's confusion about oils causes them to overlook summer oils' effectiveness as insect controls. For example, some gardeners mistakenly think all oils will burn plants, as weed oils do. It is true that a few plants are sensitive to summer oil sprays. But if you use them properly, they shouldn't cause harm,

How safe are summer oils? As safe as baby oil. A recent University of California bulletin stated, "The reason for the promotion of oil sprays in the 1980s is their innate environmental safety and low toxicity to parasites and predators. Oil degradates quickly by evaporation after application, is safe to mammals and people, and fits neatly into the concept of integrated pest management."

The way an oil is refined dictates how it can be used. Horticultural oils are manufactured through distillation. Oils that distill at lower temperatures also evaporate more quickly when sprayed on a plant, minimizing the possibility of burning the leaves. These are the summer oils. Dormant oils are distilled at a higher temperature and evaporate more slowly. They'll burn leaves if used during the growing season. Many oils sold for summer use are actually midway between the lightest summer oils and heavier dormant oils. They can be used in summer and, at a more concentrated rate, in winter. Since product labels don't list distillation temperatures, you should use an oil in summer only if the label specifically says you can.

Oils kill insects either by smothering them and their eggs, or by interfering with membrane functions.

When used to control scale, summer oils have an important advantage over other sprays. Most products are effective only when scale are in their crawler stage, usually in early summer. But oils appear to have a longer period of activity. They can be effective later in tbe summer, when the insects' shells have begun to harden. When not to use summer oils. There are times when using a summer oil will almost certainly burn a plant. In general, oil is most likely to damage young, tender growth. Here are some other tips.

Never spray a plant that is under moisture stress. Water 24 hours before you start spraying.

Never spray if the relative humidity will remain above 90 percent for 48 hours. (This would happen only in very foggy weather near the coast.)

Never spray if temperatures are expected to rise above 90' within 24 hours. If you think they might come close, make your spray half as strong as the label recommends, then spray in the evening or early morning.

Never spray plants known to be sensitive: azalea, blue spruce, Japanese holly, Japanese maple, photinia, Savin juniper (Juniperus sabina), smoke tree, walnut, or any other type listed on the label.

Insecticidal soaps: a better understanding of how they work

Soap sprays are occupying more and more space on nursery shelves, and that trend promises to continue. New ones are more relined, and some are formulated to control specific pests. The most recent addition, not yet registered in California, is a soap-based herbicide.

Originally, it was thought that insecticidal soaps were effective because their fatty acid could break down an insect's outer membranes, causing it to die of dehydration. Recent research finds that soaps may actually interrupt an insect's metabolic processes.

However they work, insecticidal soaps, like oils, are safe products that have little effect on the environment when used properly. Soaps act fast but have no residual action, so they have to be used often. Like oils, they can also burn some plants, particularly in hot weather. Some gardeners avoid burning plants by hosing them off with fresh water an hour or so after using the soap spray. Check labels carefully before using.

Sulfur: the old yellow dust takes on modern importance

The commonest use of sulfur (available as a powder for dusting plants, a wettable powder for spraying, or as liquid spray) is to control diseases like mildew, scab, and brown rot. But sulfur also kills some insects, particularly mites. This has become more important, because registration changes have made kelthane, the most commonly used miticide, difficult to find. Like insecticidal soaps and horticultural oils, sulfur is considered environmentally safe. But it can burn plants if used improperly: never apply sulfur when temperatures rise above 90[degrees], or within four weeks of using an oil spray.
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Copyright 1988 Gale, Cengage Learning. All rights reserved.

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Date:Aug 1, 1988
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