Greater awareness of soybean aphids helped to control the pest in Indiana this year, a Purdue Extension entomologist says.

"I think everyone was ready for them," Christian Krupke said.

That is because farmers now have much experience in dealing with aphids following major infestations in 2001, 2003 and 2005, when there were more than 1,000 aphids per plant in some fields. Soybeans should be treated with insecticide when aphids number at least 250 per plant.

"One of the reasons we had the outbreaks in the past is because we didn't have the awareness of aphids that we have now," Krupke said. "They don't have a free ride anymore in terms of having time to build up numbers before somebody notices them in the field."

There were indications in early August that aphids could be a problem this year in some areas, primarily northern Indiana, although a major infestation was not expected. While the summer was generally hot and humid, there was a period of ideal weather for aphid development, with temperatures in the low to mid-80s and relatively low humidity. Some fields were over the threshold in northern Indiana and Michigan.

There was concern that aphids also could become a problem in southern Indiana, where soybeans were planted later than in northern parts of the state because of very wet conditions and some double-cropped beans. The damage aphids can cause to soybeans depends not only on density of the population but also on the stage of a plant's development. Aphids will often seek out beans in earlier stages, and they can cause significant damage if left unchecked before pod fill.

Southern Indiana producers were advised in Extension's Pest & Crop report in August to be especially vigilant in scouting for aphids.

Indiana farmers who had aphids above the threshold quickly treated their fields, Krupke said.

Scouting for soybeans early in the summer is an important first step in controlling aphids. Fields near the shrubby plant buckthorn often show first sign of aphids because they winter on the plant and then move on to soybeans. Buckthorn is uncommon in Indiana, and most aphids in the state are migrants from soybeans in nearby states with abundant buckthorn, primarily Wisconsin, Minnesota and Michigan.

Early scouting and spraying when plants exceed threshold levels of aphids have combined to better control aphids in recent years.

"It has definitely fallen back in severity, which is a good thing," Krupke said.