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College of Food, Agricultural, and Environmental Sciences


Soybean Aphids Reach Economic Thresholds in Ohio

August 7, 2007

WOOSTER, Ohio -- Soybean aphids have arrived in Ohio, and counties along Lake Erie are taking the brunt of the impact.

Ron Hammond, an Ohio State University Extension entomologist, said that soybean aphid populations in soybean fields throughout north central and northeast Ohio have reached threshold (250 aphids per plant) with rising populations, and some growers are seeing aphid numbers in the thousands. If left untreated, the result could be as much as 20 to 25 percent yield losses.

"We are definitely seeing a significant soybean aphid outbreak throughout those regions of Ohio," said Hammond, with the Ohio Agricultural Research and Development Center. "We are highly recommending that any grower in those areas to check their soybean fields as soon as possible as they might have populations high enough to warrant treatment."

The soybean aphid, a sapsucker with a voracious appetite, was predicted to hit Ohio in high numbers this year. Despite those expectations, the outbreak throughout Ashtabula, Geauga, Trumbull, Erie and Lorain counties caught entomologists off guard.

"North central and northeast Ohio were just not regions that we anticipated such high aphid numbers," said Hammond. "Generally, northwest Ohio gets hit with high numbers because of aphids migrating from more northern states such as Michigan."

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 Ontario and Quebec -- regions where up to 90 percent of soybean fields have been treated due to high aphid numbers.

Hammond stressed the importance of scouting and treating fields with insecticides, especially if populations are as high as 800 or 1,000 aphids per plant.

"At the current stage of soybean development, most of the treatments are very worthwhile. The important thing is to apply them appropriately. If you get good coverage, you are going to get good control," said Hammond. "The sooner you spray at threshold the more yield you are going to save. Even if a plant gets over 1,000 aphids per plant where you'll probably have a yield loss already, you are still going to save a little bit of yield. And saving even three or four bushels per acre will pay for that insecticide treatment."

Hammond urges growers to not wait to treat if soybean aphid populations reach beyond threshold and continue growing.

"With rising population and good conditions, that 250 per plant threshold can quickly turn into 800 or 900 aphids per plant in four to seven days," said Hammond. "Aphids of 800, 900, or 1,000 or more per plant can literally suck the life out of a plant. The feeding stunts their growth, causes them to abort pods and impact seed development."

And with high aphid populations come more damage to the plants, not only with feeding injury, but also with the residue that aphids leave behind as they process plant material. As aphids feed they secrete honey dew, a sugary material that coats the plants and invites the growth of pathogens such as sooty mold.

"By the time you start seeing that honey dew on the plants, you've already taken a significant drop in yields. The presence of honey dew and sooty mold is not an indication of when to treat," said Hammond. "You should have sprayed a week or two prior to that."

Despite the high aphid numbers present throughout the lake counties, the rest of the state is not out of the woods with potential aphid outbreaks.

"We are not saying that the rest of the state is out of woods. Growers should still be scouting their fields," said Hammond. "We don't want them to get caught off guard. This situation is just very critical right now in north central and northeast Ohio."

For more information on the state of soybean aphids throughout Ohio, log on to OSU Extension's Agronomic Crops Team Web site at

Candace Pollock
Ron Hammond