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Aphids in the air: What is the risk for 2007?

Agriculture.com Staff 12/16/2006 @ 11:09am

The 2006 growing season has come to a close and with it another year's worth of experience with the soybean aphid. For many, it was a quiet, "low aphid" year with few reports of economic outbreaks within Iowa.

Reflecting these low populations in the field, we observed fewer aphids within our suction traps compared to the 2005 growing season when the traps collected nearly 100 times more aphids. For the last two years, the Iowa suction trap network has been part of a larger network of suction traps located in nine states throughout the Midwest.

Although the soybeans have been harvested, the soybean aphid overwinters within the Midwest on buckthorn. Every fall, winged soybean aphids move from soybeans back to their primary host, buckthorn. Here they mate and lay eggs, which is the overwintering stage. High numbers during the fall flight suggest a high population for the following year, and the opposite is true of low numbers during the fall flight. Fall flights of soybean aphids are presented here to give an estimate of the potential for outbreaks next summer.

To what extent the suction trap network reflects the risk of outbreaks in Iowa is not clear. This fall, moderate numbers of winged aphids were observed feeding and laying eggs on buckthorn in Ames. However, many of these aphids were being eaten by insidious flower bugs and multicolored Asian lady beetles. To what extant these predators reduce overwintering populations of soybean aphids in Iowa, and how that translates into a smaller population to infest soybeans next spring remains unknown.

As has been shown consistently across the North Central Region, insect predators have a significant impact on soybean aphid populations in soybeans. Initial attempts to predict their populations in the absence of this impact tend to overestimate soybean aphid population growth.

Finally, soybean aphids are not the only insect caught within the Iowa suction traps. A total of 18 pest species of aphids have been found in the suction traps. Of particular interest to us is the cowpea aphid. Along with the soybean aphid, the cowpea aphid is a relatively new species to Iowa and was first reported in 2002. It has a broad host range among legumes and can serve as a vector for more than 30 viruses. Outbreaks in alfalfa were reported in Iowa during the 2006 growing season.

Finally, soybean aphids are not the only insect caught within the Iowa suction traps. A total of 18 pest species of aphids have been found in the suction traps. Of particular interest to us is the cowpea aphid. Along with the soybean aphid, the cowpea aphid is a relatively new species to Iowa and was first reported in 2002. It has a broad host range among legumes and can serve as a vector for more than 30 viruses. Outbreaks in alfalfa were reported in Iowa during the 2006 growing season.

The 2006 growing season has come to a close and with it another year's worth of experience with the soybean aphid. For many, it was a quiet, "low aphid" year with few reports of economic outbreaks within Iowa.

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