Iowa soybean farmers, particularly those in central and northern Iowa, are facing an invasion in their fields. Iowa State University agronomist Palle Pedersen says when farmers find the number of soybean aphids have crossed a significant threshhold in a field, it’s time to spray.
"In some areas, they can hardly find them. In some areas, they have approached that threshhold during the past two weeks, so it varies a lot," Pedersen says.
That threshhold, according to the experts, is when a farmer discovers there are at least 250 aphids per plant. According to Pedersen, weather conditions can play a role in the infestation of soybean aphids . "But in general there are so many variables that we cannot really pinpoint out what’s going to influence it," he says.
Farmers have two options once they discover an infestation: sprayers with a high clearance that can be rigged up to a tractor and driven through a field or a crop-dusting airplane. "There’s still a lot of debate going on about which does the best job," Pedersen says. "…If the aerial applicators knows exactly what to do and how to do it, you can get as good a job with an aerial application as you can from a ground rig."
Aphids cause major problems for a soybean plant, the most dangerous is the bugs seem to foster a fungus which limits the amount of sunlight that fuels the plant’s growth. "It looks like the plant is wearing sunglasses, so you get a reduced photosynthetic rate which is extremely important because what we call the crop growth rate or the accumulation of biomass per time during the time right now is really critical for the final yield," he says.
Pedersen expects seed companies to develop an aphid-resistant variety soon. "I will not be surprised if in two to three years we’re going to have aphid-resistant lines available on the market," Pedersen says.
Pedersen advises farmers to scout their soybean fields twice a week to check on the amount of aphids in their field to determine whether it’s time to apply insecticide.