Expert says unusual growing season could cause unusual aphid cycle

WOOSTER, Ohio — While farmers across the Eastern Corn Belt persist in harvesting a late soybean crop, Ohio State University Extension experts are working to determine how the soybean aphid might affect the 2012 crop.

“This is the first fall I don’t feel comfortable making a prediction, where for the past eight or nine years we’ve done so and been correct,” said Ron Hammond, an Extension entomologist at the Ohio Agricultural Research and Development Center.

“We’re at a loss at this point to guess what might happen next year. We’re definitely going to have to keep a closer watch on it than we normally would.”

Usually

Hammond said the typical cycle observed in soybean aphid populations is a two-year rotation, with odd-numbered years exhibiting higher populations of the insect, and even-numbered years being considered off years for the pest.

While 2011 was not the most aggressive appearance of the aphid ever to manifest in the Eastern Corn Belt, the small green insect nonetheless made an appearance.

“I’m not saying everyone had economic problems, but we found aphids easily throughout the summer, and there were legitimate spraying efforts across the Midwest, including Ohio,” Hammond said. “Now we start considering how they will overwinter on buckthorn, and how many eggs we find.”

Population control

He said that in the typical cycle, aphid numbers build up on buckthorn in the fall of the odd-numbered years, but key fungi, pathogens and other predators feed on the aphids, leading to the even-numbered, off-year phenomenon. In scouting for the presence of overwintering aphids this fall, however, Hammond said the little green bug isn’t following its usual pattern.

“Across Ohio, and in other states as well, including Illinois, we are finding aphids on buckthorn already,” he said. “They seem to be doing pretty well right now, which suggests we might see them come back in 2012.”

Concern

Hammond’s biggest concern, and the key reason he is not yet ready to make a prediction on potential aphid pressure next season, is the disparity between key scouting sites across the state. He and his colleagues typically track aphid populations across four locations known for buckthorn. This year, each site sent different signals when scouted for aphids.

In other words, one site would predict one thing, and the other would predict something totally different.

He said the unusual weather patterns of the 2011 growing season could be one factor at play in the unusual aphid activity. Since soybeans were planted late and stayed greener longer, the aphids might have stayed on the soybeans longer before they moved to buckthorn.

Hammond said that might have played a role, and if so, the aphid populations might have built up in a typical pattern, but perhaps didn’t reach the level necessary to trigger the normal reaction from pathogens and predators.

Disparity

One key problem plaguing researchers and farmers alike when it comes to understanding the soybean aphid: no two years have been the same. Hammond said each “aphid year” has been quite different from other years, meaning experts haven’t seen enough years of repetition in terms of weather to know how the insect will operate in a given situation.

“We’ve been working with rootworm and corn borer since my first day as a grad student, but 10 years isn’t a long time to completely understand how an insect and its biology works, especially since half of those years aren’t high population years.”