The weather has been perfect for soybean aphid reproduction in recent weeks, but populations in the field remain low. While it's not too late for soybean aphid populations to flare-up quickly under the right conditions, but most University of Nebraska Extension entomologists believe that this will be a year with few aphid problems.
According to Wayne Ohnesorg, UNL Extension educator, aphid populations were so low last summer due to the extreme heat that researchers believe there weren't enough in existence this spring to cause many problems.
Ohnesorg told producers at UNL soybean management field days near Pierce recently that those who treat for aphids when they are not there may bring on more problems for themselves. Some farmers have made a practice of adding insecticide with a final soybean herbicide application as an "insurance treatment" for aphid problems, he said.
"Early treatments often take out natural enemies of the aphids" that are keeping their populations under control, Ohnesorg said. "Natural predators are important." He said that these insurance treatments often wipe out the aphid predators like lady beetles, lacewings and minute pirate bugs and allow a window for aphid populations to explode later on, particularly in years when most fields don't have significant populations. It is also a waste of money, he said.
UNL yield studies on seed treatments and their impact on aphid populations have proven that treatments do not effectively keep aphid numbers under control because the aphids are not present in the field when the treatments are active. Treatments work well at minimizing crop injury from other early pests like bean leaf beetles, but aphids arrive in fields late in the season, generally in mid-July to late-August, long after the usual 30-day treatment effectiveness has passed, Ohnesorg said.
While there is no known current insecticide resistance in soybean aphids, relatives to soybean aphids have exhibited resistance issues, Ohnesorg said. "This is a reason for stewardship," he said.
Keeping insecticide treatments at a minimum and only using them when there are threshold aphid populations in the field will keep the risk of insecticide resistance low.
While aphid populations are currently considered low in most prominent soybean producing counties, UNL Extension entomologists encourage producers to continue to scout fields. "I had to work to find just a few aphids in these fields," Ohnesorg said of the Pierce soybean management field site on the Mike Krueger farm. "But we can see quick flare-ups."
He said that aphid flare-ups can still occur at individual field sites under the right conditions, so scouting should be maintained until soybeans are well into R6 stage.
Field day events, co-sponsored by UNL Extension and the Nebraska Soybean Board, were also held at farm sites near Minden, York and Waterloo. UNL Extension researchers covered soybean topics like irrigation, fertilization, row spacing, weed management and insect and disease issues.
If you'd like to learn more about current soybean aphid conditions and control, contact Ohnesorg at 402-370-4044, or UNL Extension entomologist, Tom Hunt, at 402-584-3863.