Soybean aphids have been around for a few years now. We have learned a lot about them since then. The first year that we really saw high infestation levels was 2003. They were very devastating and caused much potential soybean yield loss that year. Without proper control, soybean aphids can destroy up to 40 percent of a farmer's soybean crop. Over the last couple of years we have developed better scouting techniques to determine the best time to spray. However we have still had to take control methods in several years since then. We have developed strategies to control aphids utilizing research that continues this summer. Some of this research focuses on using less insecticide than we have in the past years. Part of this research is taking a look at an insect that is no bigger than a comma. This insect, Binodoxys communis is a natural predator of the soybean aphid and could play a major role in protecting the soybean crop while limiting the use of chemical control. They are parasitic insect that insert an egg into the aphid. The egg hatches into a larva that kills the aphid, feeds on it and emerges as an adult from what becomes a mummified aphid shell. The big question at this time is whether or not the tiny Asian insect can survive our harsh Minnesota winters.
Soybean aphids are from Asia originally and they can cause significant damage to the soybean plant by sucking the nutrients from soybean plants and emitting a sticky residue called honeydew that can produce leaf mold. Under ideal conditions, aphids produce eight to 12 young per day. In four days those young are also reproducing and you can see how we can get into a bad situation in a hurry. Soybean aphids made the jump from China within the past 10 years. No one is sure how this occurred, and the problem is that while the aphids made the transition, the insect predators that helped control them in their native land were not able to make the jump and thus soybean aphids have been able to cause a lot of problems and have not had as many predators to help keep them in check. In Asia, soybean aphids are almost none existent or present at very low levels due to these predators. We do have one predator that we do have here is the Asian Lady beetle. These insects look like and are related to the common Lady bug. They are more aggressive and when we have a year where we have a lot of soybean aphids, we will see a lot of these insects. Most homeowners, especially in rural areas can tell that these insects can be a real nuisance especially in the fall of the year when they are looking for a place to over winter. They can find a way to get into your house and make a real mess. They cannot keep up with aphids when they are in high season so scientists are looking at introducing another predator to help them control soybean aphids. This takes some time and research to make sue that we do not introduce an insect pest that will cause other problems.
So where does this leave us in 2009? Aphids are starting to show up in area soybean fields. The key here is to take the time to take a look and scout your fields to see if the aphids are there and if they are at levels that need to be controlled. The threshold that we are looking at is 250 aphids per plant. This may be less (or more) than you think. Scouting is necessary because the kind of typical summer weather that we have is not always conducive to aphid survival. Aphids need warm weather and moisture, but they have a fairly narrow range of temperatures before funguses can set in and kill most or all of the aphid population. Scouting is the only way to get a handle on what is happening in your fields.