One year ago in late September soybean aphids terrorized whole communities with a winged flight that was unprecedented for as far south as it went in Indiana, ending up in southern counties. Well, OK, maybe nobody called out the National Guard, but it certainly was an unusual event. Double-crop soybeans found up with some aphids on them, but numbers generally weren't high enough given stage of growth to warrant spraying.
So the fear was that soybean aphids would be everywhere this year. That was before a couple of entomologists did late fall walks into territory where the aphids typically overwinter, and discovered that such a high population had drawn natural predators, and dramatically reduced the aphid populations. They concluded that instead of being high, the aphid population might be low starting out in Indiana this year.
That's pretty much the way things have worked out. Soybean aphids, only known as a major pest for the past decade or so, are more of a problem in the Great Lakes States, but can migrate south, normally only into the upper one-third to one-half of Indiana. However, in years when they migrate into the sate early enough while soybeans are still in the reproduction stage, they have done significant yield damage if producers haven't sprayed for them.
Du Pont Corp Protection recently issued a release noting that although soybean aphid populations are relatively low this season. Now is the time to scout for the potentially damaging pest. Should they build up numbers and go undetected, they can reduce yields.
What aphids do first is stress the plants that they feed upon, says Dan Sherrod, US Product Development Manager for DuPont Crop Protection. If aphids exceed economic thresholds, which is that point at which you can expect to make more by spraying than by not spraying for the insect or other pest, the aphids can reduce yields by up to 8 bushels per acre.
Now is the time to check every two to three days, he notes. If an infestation moves in, it normally increases in numbers very quickly due to the population dynamics of the insect. Look at 20 to 30 plants to get a food feel for whether or not aphids are present.
Aphids typically excrete honeydew substances that lead to a dark, sooty-appearing mold on the plant. Eventually, plants can become distorted. Leaves may turn yellow prematurely. If those things happen, yield loss can be substantial.
The message from DuPont is that even low aphids have been quiet so far, it makes sense to check for them rather than to find out next month when the combine rolls through that they did make a late appearance.