Integrated Crop Management News

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Spring planting conditions throughout Iowa were cold and wet, and most soybean fields were planted later to accommodate corn planting. June turned exceptionally dry, particularly in southern Iowa. Soybean aphids arrived on soybean in mid-June, as they normally do in northeastern Iowa. Hot and dry conditions in June favored twospotted spider mite colonization, particularly in southern counties. But as moisture stress subsided throughout Iowa, spider mite populations faded and soybean aphid colonization expanded. Some commercial fields experienced exponential growth of soybean aphid after bloom, especially in northern Iowa. In August, some fields in northwestern and northcentral counties had soybean aphid exceed the economic threshold. Some populations persisted until after seed set (R5–R6), but aphids quick crashed in most fields by mid-September. When insecticides were applied at full rates and had sufficient coverage, efficacy was good (i.e., >95% knockdown within three days after application) throughout most of Iowa. In some research trials near Sutherland, Iowa, poor knockdown with lambda-cyhalothrin was noted.

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Iowa State University



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