Late planting's impact on corn and soybean insects
Lately Mike Gray, University of Illinois, has received quite a few emails and calls regarding the potential impact of this season's late planting on corn and soybean insects. He can understand the interest. According to the USDA NASS Illinois field office in Springfield, only 10 percent of corn had been planted as of May 1, and just 1 percent had emerged. This compares with a 5-year average of 46 percent planted by May 1. In sharp contrast, last year 85 percent of Illinois corn was planted by May 1. He provides information for some key insect pests of corn and soybeans regarding the potential impact of late planting on economic infestations.
Western corn rootworms. Larvae typically begin to hatch Memorial Day weekend. Above-normal temperatures for the remainder of May this year could accelerate the timeline. In general, late planting tends to reduce the likelihood of economic infestations of corn rootworms. During the past few days (May 7 to 11), corn planting is progressing at an impressive clip across many areas of Illinois. Unless planting is set back again by a prolonged stretch of wet weather, he doesn't believe the slow start to planting will affect western corn rootworm densities this growing season. However, he has witnessed declines in western corn rootworm densities the past several seasons, for reasons he discussed in previous issues of the Bulletin. He intends to conduct surveys in producers' fields during 2011 to more accurately assess western corn rootworm adult levels.
Black cutworms. Fields that have been tilled and planted late this spring are more susceptible to black cutworm injury. Corn is at most risk when planted into fields that have supported dense populations of winter annual weeds, and we have certainly seen many such fields this spring. Don't be lulled into complacency just because a Bt hybrid has been planted. Large infestations of black cutworms -- anticipated this spring -- can potentially overwhelm certain Bt hybrids. He urges producers to look for early signs of leaf feeding to assess the potential threat of cutting.
European corn borers. Does anyone worry about this insect anymore? Early planting tends to favor the establishment of the first generation of European corn borers. Late planting increases potential problems with the second generation.
Bean leaf beetles. Establishment of bean leaf beetles is affected by many factors, including their ability to overwinter as adults beneath plant debris in wooded or sheltered areas. Although many areas in Illinois experienced very cold temperatures last winter, snowfall was abundant and likely provided a blanket of insulation. As bean leaf beetles break their dormancy and begin emerging from their overwintering sites, they often fly first to alfalfa fields. Early-planted soybean fields are most at risk for early-season feeding by bean leaf beetles. Because soybean planting will be later this season, I don't anticipate large economic infestations of this insect this spring. Any early-planted and isolated field of soybeans located near a wooded area is always at risk for bean leaf beetle injury.