Issue No. 8, Article 1/May 16, 2008
Insects and Incessant Rain
The wet, cool weather has not been favorable either for getting crops in the ground in many fields or for plant growth after planting. One has to wonder what effect this weather will have on insects. I'm not certain we have unambiguous answers for the questions associated with insects and wet weather or for the indirect effects of delayed planting. However, as we continue to watch the rain fall, we have little better to do than to contemplate such mysteries.
Emerson Nafziger and I drove from Urbana-Champaign to Randolph County then back through St. Clair and Fayette counties to look at some wheat fields on May 13. The number of wet, nonplanted fields--water standing in manywas disheartening. While Emerson was busy assessing the wheat fields, I thought more about the effects of the wet weather on the insects. We observed Hessian flies, cereal leaf beetle larvae, and aphids in the wheat fields we visited, although none of the insects were particularly numerous. It seemed to me that the aphids did not appreciate the wet weather. I observed numerous dead aphids and no colonies--only occasional individuals.
Although it appeared that Hessian flies in one field in Randolph County had stressed the wheat field (thanks to Dale Bermester and Mike Ellis at Gateway FS for hosting our visit), the bigger problem seemed to have been infection by the barley yellow dwarf virus. One can safely assume that numbers of aphids were larger at some earlier date.
We have discussed armyworms and black cutworms several times in previous issues of the Bulletin and indicated that both insects could be causing injury in cornfields right about now. But the incessant wet weather likely has not been conducive to survival of smaller larvae, and at the very least, the cool temperatures have slowed larval development. Nonetheless, we have to continue to pay attention to captures of adults in pheromone traps, because continuing flights may continue to give rise to numbers of larvae that will be threatening in the near future. Emerging cornfields should be examined carefully right now for signs of injury caused by either caterpillar. Slogging through mud may be unappealing or unfeasible at the moment. But if at all possible, check fields that were infested with winter annual weeds for black cutworms and fields that were infested with grassy weeds for armyworms.
As for the rest of the insect pests out there in this miserable weather--alfalfa, corn, soybean, and wheat growers all wish you the worst.--Kevin Steffey