2012 Too Dry for Many Pests
"The major natural control is a fungus that grows on green cloverworms," explained Bailey. "If you have a good green cloverworm population, the fungus moves to the soybean podworm. It can be a pest, but in most years it's simply a host for the fungus. In a dry year, you don't have as many beneficials, and growers who used an early season insecticide as a preventative took out the green cloverworms."
Bailey pointed to a growing interest in understanding pest-beneficial-plant interactions. "With soybean aphids we often don't have to spray because of a buildup of beneficials, including minute pirate bug, around 12 species of lady bugs and five or six others, like the big eye bug," he said. "If you hit soybeans with an insecticide early on, you can wipe out all the beneficials. Some years that won't matter, but if you get an infestation, it can be a problem. Because beneficials were down this past year, it will take time to build up the population in the spring. Pests will get a good start, making scouting early season even more important."
PLANNING FOR 2013
Ostlie noted the heavy snowfall that blanketed much of Minnesota in early December may bode poorly for the 2013 corn crop. Although beneficials will have a better rate of survival than with an open and cold winter, so will pests. In particular, he is concerned about overwintering corn rootworm populations. As Bailey noted with seed treatments, Ostlie pointed to poor activation of soil insecticides in the dry soils. This combined with overwintering to produce high populations into the summer. He expects a repeat in 2013 with the CRW surviving quite well.
"Where trait resistance is showing up, growers and consultants have commented that they've never seen so many corn rootworm beetles in the field as they did in 2012," said Ostlie. "With overwintering, there will be even more risk of silk clipping by western corn rootworm adults this coming summer. If they keep silks clipped to within half an inch of ear tips, you can end up with pollination issues."
Another element that Ostlie, Bailey and Krupke all noted was the influx of pests from the South with the early warm-up. Ostlie pointed out that it continued into the early summer with a variety of insects arriving on the prevailing jet stream out of the Southwest. "We saw some black cutworm infestation that we hadn't seen for many years," he said. "With the average temperature increasing, we are more likely to open up to migration earlier in the spring and be open for longer periods. It won't happen every year, but it will over the long term."
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