Thistle caterpillars are being reported in soybeans in southern and western Iowa. Extension crop specialists Mark Carlton (Albia) and Clark McGrath (Lewis) both report finding them in their areas. The thistle caterpillar is a sporadic pest of Iowa soybeans. In 1992, the thistle caterpillar was common in Iowa and caused significant defoliation in very young soybean. In 1995, they appeared again and heavily defoliated fields in eastern Iowa during the late summer. The last episode that merited attention was in 2001.
Rice, Marlin E., "Thistle caterpillars—mostly minor pests of soybeans" (2005). Integrated Crop Management News. 2379.
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