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Garden Doctor

Non-chemical Control Of Insects

February 10, 1985|PAUL B. ENGLER get the answers Q: Can you tell me whether it's true that there's a skin cleanser available to prevent a person who's been exposed to poison oak from getting a rash?--E.G., Fontana A: Recently, cleansers have been developed that will remove poison oak's oily irritants (urushiols) before a reaction can begin. It has been said that three out of four people who used one of these cleansers a few hours after exposure reported no rashes. Your pharmacy should carry these products. and Q: I know that the wind-chill factor makes me feel colder than still air would, but are plants affected in the same manner? --C.G., Santa Barbara A: Not the way people are, but in freezing weather, wind can increase plant injury by drawing moisture from the plant.

Several integrated pest-management programs for non-chemical control of insects and mites that attack commercial crops such as pears and walnuts have been devised recently. Nevertheless, few such programs have been developed specifically for the home garden with its dozens of pests and problems.

Home gardeners are, however, somewhat more fortunate than commercial growers, who plant vast acreages of the same crop (a practice called monoculture ). Even if a home gardener resorts to the use of chemical sprays to control a troublesome pest population, the non-target, beneficial insects and mites that are destroyed will be replaced quickly by insects from the same species that have survived on untreated plants nearby, provided that the gardener has sprayed infested plants only. These refugees are often only several yards away--not miles away in the case of commercial crops.

Such proximity does not mean that no attempt should be made to encourage the residence of beneficial insects and predacious mites on home properties. It is also worth noting that a home gardener is at a disadvantage if garden sprays are routinely applied, because plant hosts vary and because home-garden insecticides and miticides are necessarily broad-spectrum products. Unlike the materials developed to control a single pest on a commercial crop, home-garden sprays are not selective.

The timing of chemical controls can either help encourage beneficial species or repel them. Dormant pesticide treatments applied in the winter, for instance, are particularly valuable in promoting integrated pest management because they do not disrupt the mite-predator balance. Miticides applied later in the year tend to destroy beneficial predacious mites as well as the pest species.

By using chemicals only when pests reach damaging levels on a plant, home gardeners can contribute to a meaningful reduction in pesticide use and at the same time increase the; number of beneficial insects and mites. A certain pest level is necessary to increase the population of natural enemies. If a home gardener destroys a pest population too soon, little remains for the beneficial natural enemy to feed upon, and their reproduction is discouraged. If you tolerate some damage, you can often prevent more-serious problems once an equilibrium between pests and their natural enemies is attained.

Understanding the habits of a specific pest is valuable in avoiding the unnecessary use of pesticides. Deciduous-fruit pests, such as the Oriental fruit moth, will attack only the top half of a host tree. Consequently, there is little reason to apply chemical control to the lower half. You can best control weevils and caterpillars that hide in the soil before attacking the tops of plants by drenching the soil.

By timing the planting of a crop or of a host plant, you can frequently give that plant a competitive advantage over a pest. Gladiolus corms planted very early in the season seldom need pesticide treatment for gladiolus thrips, and sweet corn planted early can often be harvested without any necessity for corn-earworm treatment.

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