Despite entomologists' predictions for high soybean aphid populations this season, the pest posed little to no problems for most Ohio producers.
With the exception of fields in northeast Ohio, which reached threshold levels, aphid populations were low to nonexistent, says Ron Hammond, an Ohio State University Extension entomologist.
"We did not see aphid populations reach threshold levels (250 insects per plant) across much of Ohio," says Hammond, with the Ohio Agricultural Research and Development Center. "At most, aphids were averaging 20-30 per plant across any given soybean field."
Since 2001, Hammond and his colleagues across the Midwest have been following the soybean aphid and its impact on the soybean crop. The sapsucker can damage soybean fields and limit yield potential if left untreated to multiply in high numbers.
Entomologists suspect that cold weather earlier this spring helped to quell rising aphid populations.
"We started off this past spring with a lot of eggs and aphids being found on buckthorn, the insect's overwintering host. This suggested that we would see large aphid numbers this summer," says Hammond. "But then we got that cold spell in April. Our hypothesis is either the cold weather killed off the aphids directly, or there was a lot of burning back of the foliage, reducing the food supply, and the aphids died out that way. Whatever may have happened, populations in Ohio never developed like we had anticipated."
One exception was the area along Lake Erie in northeast Ohio, where aphids were being found in the thousands by August.
"If those fields weren't being treated, then the insect was definitely reducing yields," says Hammond. Yield losses can be as high as 2% in untreated fields.
Hammond speculates that a weather system that impacted the region along Lake Erie in late July might have carried winged aphids from the Canadian provinces of eastern Ontario and Quebec -- regions where up to 90 percent of soybean fields had been treated due to high aphid numbers.
"It's a situation that has taught us to take a closer look at weather patterns and how they affect the migration of insects from one state to the other, and the movement of insects within a state or within a region," says Hammond. "This is something we'll be following more closely next year."
So what is in store for soybean growers next season regarding the soybean aphid? While Hammond is not making any immediate predictions, currently the situation looks promising.
"We've been sampling buckthorn throughout several locations in Ohio and, as of right now, we are not seeing a lot of aphids. This suggests that aphid populations may be low next year," says Hammond. "Even though we didn't have high aphid numbers, it still seems to have acted like a high year where we are not seeing a lot of overwintering aphids yet. However, we will need to continue sampling buckthorn through October and November in Ohio and surrounding states before making any predictions."
Entomologists speculate that aphid populations run on a high-low cycle -- high one year and low the next.
For further updates on the soybean aphid, refer to the Ohio State University Agronomic Crops Team Web site at agcrops.osu.edu.