SOYBEAN APHID UPDATE

Quite a bit has happened on the soybean aphid front in northeast Nebraska over the last week. We observed areal jump in populations during the week of August 10 through 16. During that time some growers have opted to spray their fields and some have not. We have been "treated" to an amazing example of the reproductive potential of the aphids. Talking to quite a few consultants, growers and dealers has led us to conclude that populations have not been very high until that week.

Should you treat or not? A heavy rainfall may wash aphids off the plant, but the weather forecast as of this writing (Tuesday AM) is not very promising. Several fields scouted on Monday and Tuesday showed a huge leap in lady beetle and parasitoid numbers and we believe that many aphid populations are now stabilizing or even declining. Looking for predators, especially lady beetles, is now going to become a key decision making factor. How many lady beetles will be needed to stabilize or reduce aphid populations? Fields where we believe the aphid populations were being reduced had several hundred aphids per plant and 1 or more lady beetles per foot of row visible on the tops of the soybean plant.

The hot weather of the last few days may have reduced the aphids' reproductive potential. The aphids prefer moderate temperatures for the most rapid reproduction. When will they leave the fields? That is the big question, which unfortunately we have no sure answer for.

The Catch-22 is that the longer you wait to treat, the less likely the return on investment as the beans continue to mature and the aphids get nearer the time where they will leave the fields to search for overwintering sites. At the current time with most beans in the R5 stage we feel that at least 400 or more aphids per plant would be necessary to get a possible economic return from treating (this is assuming that populations are still increasing in that particular field). Fields that are delayed in maturity (less than R5) may benefit more from treating as the yield potential may be affected more.

The bottom line is that this is a brand new problem behaving in a way that has not been seen before. We can only make educated guesses, put out test plots, and make careful observations that will help in future decision making.