People throughout Illinois and in adjacent states have taken note of very large numbers of grasshopper nymphs in roadsides, ditch banks, grass waterways, and, in some instances, crop fields. Larry Martin, with Monsanto, observed many grasshopper nymphs in Wayne and Fayette counties. In one field in Wayne County, the grasshoppers were "deep into the field," despite lush waterways and fencerows.|
Continued hot, dry weather does not bode well for crops when grasshoppers are numerous. As the nymphs consume noncrop hosts and these plants dry out, they will move into adjacent fields of corn and soybeans, potentially causing serious defoliation. Monitoring noncrop areas near crop fields and watching for injury along the field margins will be vital during the next few weeks. As the grasshoppers grow, they consume more food, so the amount of damage can increase dramatically in a relatively brief time.
As I indicated in last week's Bulletin (issue no. 14, June 28, 2002), you can control grasshopper nymphs in noncrop areas before they move into adjacent crops, or you can control them when they begin to invade crop fields. Although I provided economic thresholds, I will yield to some sage advice from a couple of seasoned entomologists. Marlin Rice, extension entomologist at Iowa State University, and Kevin Black, with Growmark, have pointed out the futility of trying to count grasshoppers per square yard. (It's possible that these guys simply can't count very high, but we'll assume that counting grasshoppers is just too difficult to do.) Both of them urge common sense for making decisions about controlling grasshoppers. I concur. Insecticides suggested for control of grasshoppers in alfalfa, corn, and soybeans are presented in Table 1. Please follow all label directions and precautions.--Kevin Steffey