Protecting the Environment

by James Krysan, Leslie McDonough, Alan Knight, and K. Duane Biever, Research Scientists, Agricultural Research Service, Yakima, WA; Charles R. Brown, Research Geneticist, Agricultural Research Service, Prosser, WA; and James Kamm, Research Entomologist, Agricultural Research Service, Corvallis, OR.

In the mid-20th century, agricultural science presented farmers with a class of "miracle" tools: synthetic, or manufactured, chemical pesticides. Pesticides helped farmers profitably produce an abundance of high-quality food and fiber. But there are concerns that those "miracle" products, as used, can have undesired side effects for the environment and human health. Future farmers must look for ways to produce the expected quality and quantity of food and also to eliminate, or drastically reduce, the causes of these environmental and health concerns.

The Problem

Most of today's synthetic chemical insecticides kill target pests by poisoning their life functions. Materials that are toxic to nearly all animals are called broad-spectrum insecticides. When they are applied, nontarget animals that happen to be in the environment are also affected. When misused, such pesticides can pose hazards to humans.

Aside from environmental and safety concerns, these pesticides have a doubtful long-term usefulness because of the speed with which many pests become resistant to them. Resistance is especially prone to develop when a pesticide is used as the single method of control on generation after generation of a pest. Often, after several generations of such exposure, the pesticide no longer works.

Science must devise ways to control pests while affecting little or nothing else in the environment and, for good measure, make it tough for the pest to adapt. This is not a pipedream.

Some solutions are here now, and others are on the way. These new, environmentally benign ways to control pests are the product of novel applications of advances in scientific knowledge.

Agricultural Science Responds

Some caveats exist in this search for environment-friendly products and approaches that farmers can use in farming profitably and in providing future consumers with ample supplies of attractive, tasty, and wholesome foods. First, it is critical that the control method be as specific as possible for the target pest. The goal is for nontarget life to be unaffected. Second, several different tactics should be integrated to solve the pest problem. An integrated approach reduces the possibility that the pest will quickly develop resistance. The development of the tactics will depend on a profound basic knowledge of the pest, its natural enemies, and the entire agroecosystem.

Third, all chemicals should not be ruled out just because many existing and past synthetic pesticides with problems are chemicals. Such a broad indictment is illogical: living things themselves area complex mixture of dissolved and structural chemicals supported by a continual intake of nutrients and energy in chemical form. It follows that many schemes for affecting living systems will have a chemical component, and we should expect highly specific chemicals to be part of environmentally benign pest control.

The following case studies examine innovative methods of pest control. These techniques represent just a few of the many that are available for farmers to use.

Protecting Cabbage

Keeping pests out of cabbage is a tough job, and devising ways to protect cabbage in an environmentally benign way is a difficult challenge. Several pests attack the crop each year, and the final marketable product must be essentially free of insect damage. Therefore, many applications of broad-spectrum pesticides are routinely applied to achieve control.

Consequently, in an effort to cut back on the use of broad-spectrum insecticides, entomologists have worked for two decades to develop biological ways to control butterfly and moth (lepidopteran) pests of cabbage and related crops. These pests include the imported cabbage worm, the cabbage looper, and the diamondback moth.

The trick is to obtain compatible biological agents that together will control all the pests on the crop. Broad-spectrum pesticides are unlikely to be acceptable because they are generally toxic to many helpful biocontrol agents that is, the pest's natural parasites and predators. Even one such application during a season can destroy the natural-enemy complex.

In a 1991 field test in the Lower Rio Grande Valley of Texas, an environmentally benign, biologically based method with no hazards to human health succeeded in controlling cabbage insect pests. The method has three major components: (1) methods to allow the grower to determine how many of each pest are present in the patch at any one time; (2) insecticidal materials that do not kill natural enemies (such as parasites) that attack the pests; and (3) a source of parasites of the pests to permit "inoculative" releases that is, release of the parasites into the field to flourish and reproduce so subsequent generations will control the pests. To continue the medical analogy, the parasites prevent, and the insecticides cure.

Cabbage worm.

Doug Wilson/USDA 90BW1468-2

Pests that attack cabbage crops each year include the cabbage worm (top), cabbage looper(bottom), and diamondback moth. The objective for protection is to obtain compatible agents that will control all pests on the crop. A benign, biologically based insecticide produced by a common soil bacterium, Bt-endotoxin has succeeded in controlling cabbage pests.

Diamondback moth.

Doug Wilson/USDA 90BW1465-9

Cabbage looper. USDA/ARS 1087X1150-9