2012 Too Dry for Many Pests
The past year was a tough one for crops in a lot of states. In the drought-stressed Midwest, it was just as tough on bugs—both pest and beneficial. The season started off well. A mild winter with a good snow cover improved overwintering survival of pests and beneficials alike. The early warm up could have set the stage for high insect populations, but the cold snap that appeared to threaten a lot of early planted corn knocked bugs back as well.
"Insects like nothing better than a nice, mild progression in the spring," said Ken Ostlie, Extension entomologist, University of Minnesota. "Dramatic temperature swings when the snow cover is gone can help turn the insect issue around a bit."
WHAT HAPPENED TO SOYBEAN APHIDS?
For some insects, the early spring was too much of a good thing. As temperatures warmed, insect life cycles shifted into high speed with faster maturation and reproduction. The problem was the absence of plant material at the right time. In Minnesota, which reported unusually high soybean yields in some areas, soybean aphids got snookered, suggested Ostlie.
"The early bud break on the overwintering host buckthorn had soybean aphid populations reproducing fairly early," he said. "The late freeze caught them and knocked the population back. Then we had rainfall during colonization that combined with delayed soybean planting in some areas. When the aphids were ready to make their move, the soybeans weren't there. When the soybeans were there, heavy rainfall washed the newly established aphid colonies off because the canopy was not developed to protect them."
The one-two-three punch effectively knocked aphids out for the season in many parts of Minnesota. While not as dramatic, other areas also saw the soybean aphid set back on its heels. "There weren't soybean aphids in our fields or reports of them," said Christian Krupke, Extension entomologist, Purdue University. "A lot of insects need free water, either dew or rain to keep them hydrated. There was neither in much of Indiana for most of the late spring and through summer. It was a rough summer for many things, not just crops."
Although his state's soybean growers didn't see aphids, they did see plenty of mites. However, the weather turned around, and the soybeans outgrew the mites, repelling them. While the mites might then have turned on corn, it was too late in much of Indiana—and elsewhere.
"Some mites stressed irrigated corn, but lots of dryland corn was already dead by the middle of July and not of interest to the mites," said Krupke. "Insects like stressed plants, but not dead plants."