Published: July 29, 2008 02:03 pm            

Prime time for aphids

Field scouting important to determine threshold

Soybean aphids have been around now for a few years, and we have learned a lot about them since their arrival.

They were particularly devastating in 2003 when they had their first real year of infestation in south central Minnesota. Since then we have been developing strategies to control them. However, research continues to see what we can do to control them without having to use as much insecticide as we have in the past.

Soybeans originated in China and other parts of Asia. They were imported here many years ago because of their versatility and many uses both as livestock feed and human food. For many years soybean plants were used as hay on area farms. For the past 40 years or so they have become an important part of our local crop rotation and almost every farm raises significant acreages of soybeans.

Soybean aphids made the jump from China within the past 10 years. No one is absolutely sure just how they made this jump. The problem here is that while the aphids were able to make the transition, the insect predators that help 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 control population as are needed.

In the Asian countries that raise soybeans, soybean aphids are almost non-existent or at low numbers due to these predators. One predator that is in the United States in great numbers 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 you that they can be a real nuisance especially in the fall of the year when they come out of the fields and are looking for a place to overwinter. They will look for a place to spend the winter and often times will come into your house and make a mess.

So where does that leave us in 2008?

Well, the aphids are definitely here. If you haven’t checked your fields to determine not only whether or not you have aphids but also what population levels are out there it would be worth your effort.

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 population.

Aphids are incredibly resilient. As a matter of fact, aphids are all females and are born pregnant. They can have many babies in a few days and can double and quadruple their populations in just a few days. However, this can also turn around just as quickly as the weather changes and temperatures and moisture levels allow aphid levels to plummet.

That is why you need to spend some time in your fields looking at plants and seeing what is actually out there.

        

• Click to discuss this story with other readers on our forums.