Insects are always a problem in fields during the summer, but the best way to control them is by simply watching for them.
One, the western bean cutworm, fairly new the region, said Christian Krupke, a Purdue University entomologist. In addition to monitoring fields for western bean cutworm larvae, farmers can set pheromone traps to tell if female moths are in the area. Field scouting helps as well. Scouting should include at least 20 plants throughout the field, and if 5 percent of the plants scouted have been infected by the insect, Krupke advises spraying.
Farmers also should look for corn rootworm, the larvae of which can damage the roots of corn plants. The corn rootworm can harm cornfields if not controlled by using insecticides or Bt hybrids labeled for rootworm control.
The soybean aphid is the most likely pest to be in soybean fields this summer. The largest populations fly in from Wisconsin and Minnesota to colonize in Indiana and move into Ohio. Although they will start to increase in July and August, they should be monitored now.
If farmers scout soybean fields and find an average of 250 aphids per plant, Krupke said the fields should be treated. He urged farmers to be wary of spraying too early because the field treatment can harm beneficial insects feeding on aphids. This will then cause aphid populations to increase quickly once the residual effects of the insecticide have gone.
“Spraying too early can be harmful to the plants in the long run,” Krupke said. “A hundred aphids on a plant today does not mean there will be 250 a few days later.”
Fields most susceptible to pests are those planted significantly earlier or later than those around them. Also, cornfields that are on a continuous corn rotation are more likely to have insect problems, Krupke said.
For more information, visit http://extension.entm.purdue.edu/fieldcropsipm for information on field crops entomology and http://extension.entm.purdue.edu/fieldcropsipm/corn.php for the corn insect scouting calendar.