Integrated Crop Management

Cabbage loopers emerge from soybean

At least one of the mysteries of caterpillars in soybean has been solved. Loopers were reported from several fields across the state during mid- to late June, but the exact species of looper was not known. I collected pupae (cocoons) from soybean in Marshall County on June 22. On June 30 and July 1, cabbage looper adults emerged. Thus, the cabbage looper was causing some of the problems, although it is still possible that additional species of loopers may have defoliated soybean in other counties. Cabbage loopers have a white "octopus-shaped" spot on the forewing. These moths may become common at lights during the next week.

An obvious question is should more problems from loopers be expected this summer? I think some defoliation during July from the next generation of loopers can be expected. I do not anticipate the cabbage looper developing into a serious problem, relative to the number of acres infested, but some fields may need to be scouted. Fields that would benefit from field scouting in July will be those that have marestail. This weed attracted moths to many no-till fields during early June and the larvae caused substantial defoliation. A field should be scouted if marestail is still growing in that field. A threshold for blooming-stage soybean is that any species of caterpillar should be controlled before defoliation exceeds 20 percent of the leaf area.

Marestail

Marestail was abundant in many no-till soybean fields that were defoliated by cabbage loopers.


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Cabbage looper adult with white octopus-shaped spot on wing.

This article originally appeared on page 139 of the IC-486(17) -- July 9, 2001 issue.


Source URL:
http://www.ipm.iastate.edu/ipm/icm//ipm/icm/2001/7-9-2001/cabbageloopers.html