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College of Food, Agricultural, and Environmental Sciences


Low Soybean Aphid Populations Predicted

January 26, 2006

WOOSTER, Ohio -- If soybean aphids continue their annual alternating high and low population cycles, Ohio soybean growers could see very few of the insects this growing season.


Ohio State University research entomologist Ron Hammond said that fall sampling and current observations point to low aphid populations for Ohio. Soybean aphid populations were high last summer, triggering treatment of soybean fields where thousands of aphids per plant were being found.

"There were a lot of winged aphids flying in July and August, but very few were found in the fall months. One of the thoughts is that the multicolored Asian lady beetle wiped them out," said Hammond, with the Ohio Agricultural Research and Development Center. "We also did some sampling of buckthorn, a known overwintering host, and found little or no aphid colonies. We are not saying that we are not going to have some aphids out there, but if it follows what we've been seeing the past few years, the numbers should be low."

By "low," Hammond refers to populations below the threshold of treatment: 250 aphids per plant. Any numbers higher than that could mean major damage or devastation for the soybean crop -- anywhere from a loss of five bushels per acre to as high as 18 bushels per acre.

"We are still going to continue to look for them, and we are recommending that growers scout and monitor their fields. That's all part of an Integrated Pest Management program," said Hammond. "What this all means is that we may not have to take any preventive measures this spring."

One of those preventive measures is to apply seed treatment at planting. Insecticides, such as Cruiser and Gaucho, have been labeled for controlling soybean aphid. However, Hammond said that recent OARDC research has shown that such at-planting seed treatments are ineffective for the aphid.

"The problem is that one would apply the treatment in early or mid-May and the aphid doesn't show up to be a potential problem until mid-to-late July. That's too far of a time spread for the treatment to have any impact," said Hammond. "Another problem is the potential for not enough aphids to show up to warrant sufficient control. Our research showed that there was no difference in performance between treated plots and untreated plots under this situation. The treatments might prevent aphids from reaching threshold for about a week or two, but a grower will need to treat those fields sooner or later if the aphids are building."

Another preventive measure being recommended by some is to apply a fungicide/insecticide combo. But research with Ohio State's Department of Plant Pathology has shown that such a treatment, specifically a Quadris/Warrior combination, has been shown to boost soybean yields only in fields with high soybean aphid populations.

"There is no doubt that if you have high soybean aphid populations, a grower can save anywhere from five to 18 bushels per acre with such treatments," said Hammond. "However, we don't recommend general sprays just for plant health purposes."


Candace Pollock
Ron Hammond