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Soybean aphids on the move in eastern Corn Belt

Agriculture.com Staff 07/01/2009 @ 11:57am

Soybean aphids continue to pop up -- though in low numbers so far -- in early-planted soybean fields in the eastern Corn Belt.

But, their presence at this point in the growing season indicates the pest will reach the treatment threshold fairly soon, says Ohio State University (OSU) Extension entomologist Ron Hammond.

Hammond and fellow OSU researchers Andy Michel and Bruce Eisley have recorded aphid populations around northern Ohio, where the soybean crop is mostly in the the V5-V6 growth stage. Aphids have also been noted further north in Michigan and into Canada, the researchers note.

"Early-planted fields with soybean aphids, currently in the V5-V6 growth stages, are beginning to get flowers. These fields will be in the reproductive stages, R1 and R2 or flowering, within a very short time," Hammond says. "These are the stages where the threshold is an average of 250 aphids per plant with a rising population. Thus, for those fields with soybean aphids, the normally used threshold of 250 aphids will be reached shortly."

So, will the bugs march into your fields like an invading army later this summer? Hammond says it depends on several factors, the major one being whether or not you applied a seed treatment at planting. Those protected with seed treatments like Cruiser, for example, will likely be better protected, at least for some time.

"The thought is that insect control will only last 45-60 days. Being that fields with aphids were most likely planted the first week in May, the seed treatments have lost or are about to lose their efficacy," Hammond says. "In other words, seed treatments should not be counted on to provide any control from this point on, including when winged aphids begin to make their appearance in mid to late July."

If your protective measures do run out before aphids hit, don't get too overzealous with treatments either, Hammond advises. Take a more surgical approach with insecticide treatments, as insurance or prophylactic treatments can sometimes do more harm than good.

"First, there is no way to predict which fields, let alone which area of the state might have economic outbreaks of the soybean aphid," he says. "There is too great a chance for wasting money. Secondly, the only thing that insecticides will assuredly do at this time is to kill beneficial insects that could prove valuable in helping prevent outbreaks of aphids later in the summer. Removing those 'good' insects early can only cause more harm than good."

Soybean aphids continue to pop up -- though in low numbers so far -- in early-planted soybean fields in the eastern Corn Belt.

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