   Insecticides and Their Use - June 21, 2000 Jeff Schalau, County Director, Agent, Agriculture & Natural Resources Arizona Cooperative Extension, Yavapai County Insects become pests for a variety of reasons. First, insects can be accidentally (or intentionally) introduced to areas outside of their native range where they escape the controlling influence of their natural enemies. Second, they can be harmless until a plant or animal disease is introduced into their range that they are able to transmit (i.e. malaria). Third, we can introduce non-native plants, such as crops, and the native insects change their food preferences. Fourth, we crop the land so intensively that benign species or minor pests become major pests. In all of these cases, some form of pest management can become a necessity. Often we reach for a synthetic insecticide to solve our pest problems. Synthetic insecticides are valuable tools in the production agricultural setting. Commercial operators are highly trained and monitor action thresholds before pesticide applications are made. In the backyard setting, we also need to monitor pest activities and damage levels before we take action. This means tolerance of some pest damage and positive identification of the pest when damage levels warrant action. Synthetic insecticides were developed and came into widespread use during and after World War II. DDT was the first of these chemical compounds and was introduced as an insecticide in 1939. By the late 1940's, insects had started to develop resistance to it. DDT is also highly toxic to fish and accumulates in the fatty tissue of animals. For these reasons, DDT was banned from use in the United States in 1973 (it is still in use in some countries). During the years of widespread use, DDT is estimated to have saved 25,000,000 human lives by killing mosquitoes that spread malaria and lice carrying typhus. Since DDT, synthetic insecticides have become less toxic to non-target organisms. For the remainder of the column, the focus will be on specific synthetic insecticides, their advantages and disadvantages. Malathion is probably the safest of the widely used synthetic insecticides. It remains effective for one to three days. It controls aphids, scale insects, mealybugs, leafhoppers, whiteflies, cucumber beetles, and many other insects that feed on exposed plant surfaces. It is especially useful on vegetables, and because of its short life, is less toxic to non-target insects. Diazinon can control insects for up to a week after application. This makes it more effective against insects that hide or migrate into your garden. It is also more toxic to beneficial insects and bees than malathion. Diazinon controls a wide variety of insects in orchards and vegetable gardens. Use care when applying diazinon near water as it is hazardous to aquatic organisms. Carbaryl (Sevin) is not highly toxic to humans and quite effective against many insects. It is more toxic than either malathion or diazinon to bees and beneficial insects, so its use should be avoided whenever possible. It should not be applied to flowers and other plants visited by bees. Carbaryl comes in bait forms are less likely to cause damage to non-target insect population. It is especially toxic to natural enemies of spider mites and outbreaks of spider mites can often be traced to the use of carbaryl. Carbaryl remains on plant surfaces much longer than most other insecticides available to homeowners. For this reason, it is useful for controlling difficult pests such as codling moth. Although the focus of this article was synthetic pesticides, don't forget that there are many other insect control options that can be less toxic to non-target organisms. Among these are: horticultural oils that work mainly through suffocation; dormant oils that control over-wintering pests; soap sprays; sorptive dusts such as boric acid, silica gel, and diatomaceous earth; sulfur dust which can offer some control against mites as well as many fungi; and microbial insecticides such as Bacillus thuringiensis; and botanical insecticides such as pyrethrums and neem tree oil. When applying any of the above listed products, always read the entire product label, wear the proper personal protective equipment, and apply at the proper time and under the proper environmental conditions. The University of Arizona Cooperative Extension has publications and information on gardening and pest control. If you have other gardening questions, call the Master Gardener line in the Cottonwood office at 646-9113 or E-mail us at mgardener@kachina.net and be sure to include your address and phone number. The Yavapai County Cooperative Extension web site is http://ag.arizona.edu/yavapai/. |