Seed treatments and alternatives for insect control in soybeans

(Also see seed treatments (general) and for corn and sorghum.)

Two insecticidal seed treatments are now available for soybean producers in Nebraska: Gaucho (Bayer CropSciences) and Cruiser (Syngenta). Both are neonicitinoid insecticides used to control early season insect pests of soybean. The active ingredient in Gaucho is imidacloprid and in Cruiser, thiamethoxam. Cruiser will be sold as Cruiser Maxx Pak, which includes the fungicide Apron Maxx RFC.

Treated soybean seed. (Photo by Brett Hampton)

Both products show excellent early season control of leaf feeding and sap feeding insects because of systemic activity that distributes the insecticide through the plant; however, producers should consider how these products fit into Nebraska soybean production.

Our major early season soybean insect pest is the bean leaf beetle. In the early spring the overwintered beetles become active and often enter soybean fields as soon as plants emerge. Although the defoliation the beetles cause can appear quite severe, research in Nebraska and elsewhere has shown that it usually does not result in economic damage. Soybean plants can compensate for a large amount of early tissue loss, so it takes a considerable amount of beetle feeding (generally over 50% defoliation) to impact yield. A possible exception to this may be in early-planted fields, particularly when the plants emerge well before surrounding fields. Because the beetles move to soybean fields so soon after seedling emergence, early-planted fields will usually have more beetles and suffer the most injury. For those who regularly plant before most of their neighbors and have a history of high beetle numbers and/or bean pod mottle virus, insecticidal seed treatments may be an option. Both Cruiser and Gaucho have proved efficacious against early season bean leaf beetle in our insecticide trials.

The other soybean insect pest that some have suggested can be controlled with insecticidal seed treatments is the soybean aphid. Although early season aphid mortality and sublethal effects have been observed with insecticidal seed treatments, we do not recommend seed treatments for controlling soybean aphids in Nebraska.

To date in Nebraska, the soybean aphid has not been an early season pest; it has been a late season pest. Most of our soybeans are planted in May, and we generally don’t begin to see aphids until mid to late July, well past the early vegetative stages, and in most fields soybean aphid populations peak in August. This is too long to expect currently available seed treatments to have a significant effect. In addition, not all Nebraska soybean fields will have economic populations of soybean aphids, including northeast Nebraska where we have seen the most soybean aphid injury. In Nebraska, one well-timed foliar insecticide application, based on two or more field visits, will adequately control soybean aphids and protect yield.

Keith Jarvi
IPM Extension Assistant
Tom Hunt
Extension Entomologist
Both at the Northeast REC
Bob Wright
Extension Entomologist
UNL-Lincoln

Copyright 2006 by the University of Nebraska

Published by University of Nebraska Cooperative Extension in the Institute of Agriculture and Natural Resources Cooperating with the counties and the U.S. Department of Agriculture

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