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Migrating from Asia to the US nine years ago, the soybean aphid has become one of the most feared insects in the Corn Belt and other bean-producing areas. This aphid has been confirmed by USDA in Delaware, Georgia, Illinois, Indiana, Iowa, Kansas, Kentucky, Michigan, Minnesota, Mississippi, Missouri, Nebraska, New York, North Dakota, Ohio, Pennsylvania, South Dakota, Tennessee, West Virginia and Wisconsin and in the Canadian provinces of Quebec, Ontario and Manitoba.
Midwestern growers should be prepared for the third straight year of soybean aphid invasions. It’s not a guarantee, but the trend of aphids as perennial pests has certainly been set, says Iowa State University entomologist Dr. Matt O’Neal.
USDA says that in 2008 the soybean aphid “went west,” reaching the western most cultivation of soybeans in the US in Wyoming. More than 8500 soybean aphids were caught in the Midwest suction trap network in late September
Soybean aphids caught in the traps during September and October were migrating from soybeans to buckthorn where the overwintering eggs are deposited. “This number exceeds any seen in previous years during the same time period,” says USDA.
The tiny terrors saw the on-again, off-again cycle broken in 2008.
“In the fall of 2007, we collected very few aphids after the growing season,” says O’Neal. “We thought 2008 would be a quiet year. It wasn’t. I try not to make predictions, but now we may be in a period where soybean aphid outbreaks may be more intense. It may not be a cycle. It may be every year.”
Aphids were first seen in the US in Wisconsin in 2000. “They come from a region of China with a climate much like the Midwest,” says O’Neal.
After emerging here, there was an apparent soybean aphid cycle throughout the Corn Belt. Populations would be low one year, followed by outbreaks well above the economic threshold of 250 aphids per plant the next year. There were small outbreaks in 2006 followed by the large invasion in 2007. So entomologists and growers expected a light year in 2008.
O’Neal says Iowa State research on 36 separate farms is helping researchers and growers learn more about the aphid cycle. It has led to several hypotheses from O’Neal on why 2008 was a bad year for aphids.
“First, the spring of last year was wet and cold and delayed planting,” he says. “That may have disrupted the predator relationship with aphids. We have also found that as the amount of corn and soybean production increases around a soybean field, the amount of predation decreases (as there are fewer predator insects, like lady beetles, that eat aphids due to a lowered number of field borders).”
O’Neal adds that growers who spray insecticides to control other insects may also have reduced predator numbers. He says a well-rounded integrated pest management program is needed for best aphid control. That program could include the use of new aphid-resistant soybean varieties that are coming on line.
O’Neal and others in the North Central Soybean Research Program authored a Soybean Aphid handbook sponsored partially by the Iowa Soybean Association. For more on the publication, go to www.iasoybeans.com/checkoff/publications/aphidbrochure/multiprongattack.pdf.
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