While it's been a relatively quiet year so far for soybean aphids, there are some reports of aphids hitting threshold levels in parts of the Midwest.
Purdue Extension has confirmed reports of soybean aphids at levels over the treatment threshold of 250 aphids per plant in LaPorte county in the northwest part of the state. Along with several other fields in the area in the high double-digits this week, it's likely there are more to come.
Last week, we found our first aphids in sentinel plots in Indiana and this week brought some higher populations," says Christian Krupke, Purdue University entomologist. "It appears that we may see a late push from aphids.
"However, time is on our side. Once fields hit R6 stage, aphids are not a concern. With most Indiana fields well into R3 or R4, we are not too far off."
Growers in northern parts of Ohio were urged earlier in the week to prepare for a possible boost in aphid levels. While in the previous week there was a lack of aphids, a visit to a Geauga County field found numerous soybean fields nearly 100% infested.
While the numbers of soybean aphids per plant were not yet high, nearly all plants had aphids, ranging from a few to 10 to 15 per plant. With many of the soybeans in that area being planted late and just planted late and just now in growth stage R2, growers were being reminded that they are not out of the woods, yet.
"This is especially true for growers in north central and northeast Ohio, who should make an extra effort to sample their soybeans," says Ron Hammond, Ohio State University entomologist. "If, and it is a big if, aphid populations starting doubling, these fields could be reaching threshold within the next 1 to 2 weeks."
Penn State entomologist John Tooker says recent warm temperatures have been perfect for soybean aphid development and, as a result, populations have grown toward the 250-aphids-per-plant economic threshold.
"We are aware of several fields in central Pennsylvania that easily exceed threshold and we have even found plants with close to 1,000 aphids," Tooker says. "This is not an insect that can be diagnosed from the truck of a vehicle, so get out and walk those fields."
Eileen Cullen, University of Wisconsin entomologist, says that economic threshold field averages (250 aphids per plant) were reported this past week near River Falls and Colfax in the western part of the state. There were also reports of economic thresholds in the southern part of the state between Milwaukee and Madison.
"We're urging growers to continue to scout fields through R5 soybean growth stage," Cullen says. "A lot can happen with soybean aphid during August. In 2008, we saw numbers increase most during August, particularly on later-planted fields."
Likewise in Minnesota, considered the heart of soybean aphid country, reports of aphids exceeding threshold levels were beginning to appear. Field staff in the northwest and central regions were reporting winged aphids common in many fields, the Minnesota Pest Report noted.