Business as Usual With the Soybean Aphid? Not This Year

December 1, 2009

WOOSTER, Ohio – Just when entomologists think they have the soybean aphid figured out, the minute sapsucker throws a monkey in the wrench.

Ron Hammond, an Ohio State University Extension entomologist with the Ohio Agricultural Research and Development Center, said that 2009 was such an unusual year for the soybean pest that he's hesitant to predict what's in store for growers next season.

"For the first time, at this point, I'm not really sure what will happen in 2010," said Hammond.

The soybean aphid, whose voracious appetite can greatly damage untreated soybean fields, came on the scene in Ohio in 2001. Since then, it has taken growers on a rollercoaster ride of high populations one year and low populations the next. This season was predicted as a "high" year, with aphids expecting to settle in fields across northern and central Ohio as they migrated south from Canada and Michigan. But the season didn't turn out quite as Hammond and his colleagues had predicted.

"We started seeing aphids early on in the season and thought they'd build up in the northern part of the state. The aphids built up heavy in northeast Ohio and in some locations along the lake, but nowhere near what we had expected," said Hammond. "By contrast, we found aphids in southern Ohio for the very first time and beyond threshold numbers. Aphid populations throughout central Ohio were practically nonexistent, so we are not sure where those populations came from."

Hammond said that other states throughout the Midwest were experiencing the same phenomenon: lower-than-anticipated aphid populations in the north and exploding populations across southern counties with the central part of the state generally void of the pest.

In addition, cooler-than-normal summer temperatures in Ohio pushed the flights of winged aphids into late August/early September, when populations normally take flight to their overwintering host of buckthorn in mid-August.

"In a normal 'high' aphid year, winged aphid populations would die down and we wouldn't see much on buckthorn, suggesting a 'low' aphid year the following season," said Hammond. "But the late flights lasted so long that we suddenly had incredible numbers on buckthorn and we anticipated seeing a lot of eggs. We thought that this would break the cycle of high populations one year and low populations the next."

But then a curious thing happened. A fungal pathogen, at the right place and the right time, wiped out much of the winged aphids on buckthorn. The result: Very few eggs were found after all.

"So we are heading into winter not really having a clue what's going to happen," said Hammond. "Are we going to continue our two-year cycle where we won't have problems in 2010, or was there enough overwintering of aphids to potentially generate high populations next year?"

Hammond said that growers should stay tuned to OSU Extension's Crop Observation and Recommendation Network (C.O.R.N.) newsletter for their cue to begin scouting for soybean aphids in their fields next year. The best way to manage the soybean aphid is to become more knowledgeable about the insect's biology, know when to scout, and to carefully time foliar insecticide applications if treatments are warranted. The economic threshold of aphids is 250 insects per plant.

"We'll begin sampling fields in June to see if we have early aphid populations and that will determine if we will follow a typical low year," said Hammond. "We know now that we have to pay more attention to southern Ohio. In the past we didn't worry about southern counties, but we are not going to be able to take that approach the next time around."

The C.O.R.N. newsletter can be accessed at the following Web site: http://agcrops.osu.edu.

Author(s): 
Candace Pollock
Source(s): 
Ron Hammond