Part 2, Section 2: Corn Pest Management
Corn Pest Management
INSECTS
Nonpesticide methods of insect management in corn
Insecticides should be used only as a last defense against insects, when all other methods of keeping their numbers below economic thresholds have failed and when no other control tactic exists. Corn growers have numerous strategies other than insecticides to manage insect populations, including rotating crops to break insect life cycles; using resistant varieties (including new bioengineered hybrids); eliminating insect-attracting weeds at least 10 days before planting; moldboard plowing, harvest, and removal of insect-harboring ground covers; adjusting planting dates to avoid key insects; adjusting harvest dates to minimize crop losses; irrigating to help the plant compensate for stresses caused by insect feeding; using good crop management techniques (fertilization, weed management, seedbed preparation, etc.); selecting well-adapted hybrids; and mowing pest-harboring weedy areas around the field. The specific combination of these techniques that a farmer uses depends on the set of key insect pests he or she must manage. Some of these insect management tactics often are implemented by farmers because they are good crop production practices, regardless of their insect management benefits.
A farmer who is scouting or having his or her fields scouted on a regular basis has a pretty good idea which pests occur most frequently on his or her farm. Pest history and a knowledge of the relationship between a pest and a field characteristic can be used to select the best set of nonpesticide practices. For example, a farmer might be having repeated problems with western corn root-worm, European corn borer, black cutworm, and slugs. Other insect pest species rarely cause problems. From field records and discussion with the farmer, we learn that a field has been in no-till corn for two years and has had an increasing problem with common chickweed. Before the field was in corn, it was in a grass-legume mixture for five years. Observation of the field tells us that it is in a low-lying area near a stream.
Through research and experience, insect management experts have learned that corn rootworm populations build up in continuous corn and that rootworm larvae can survive only on corn roots. These experts also have learned that black cutworm populations often are associated with common chickweed. Slug populations are known to increase in perennial crop systems. European corn borer moths prefer areas with high humidity and low wind speed, such as those typically found in lowlands along streams and rivers. By understanding the environmental requirement of each pest, the farmer can select tactics to manage it.
A possible long-term noninsecticide-based management program for this set of pests might include the following: 1) to minimize corn rootworm population buildup, implement a crop rotation that includes only one or two years of corn; 2) to manage European corn borer in years when corn is grown, select a Bt-corn hybrid with good agronomic traits for the farm; 3) to minimize the likelihood of crop injury from black cutworm, till or apply a burndown herbicide at least 10 days before planting corn; and 4) when rotating from a long-term perennial crop to corn, spring- or fall-till the field to eliminate slug shelters. A fall burndown of the hay field also may help eliminate slug populations.
This is one of a number of possible insect management programs that could be used to manage this complex of pests. Which set of management tactics a farmer selects is controlled by a number of variables, such as the farmer's equipment, the crop needs, time constraints, etc. Regardless of the design, no insect management program is ever 100 percent effective; therefore, insecticide applications always will be needed as a backup when other methods fail to keep insect populations under control.