On May 23, John Shaw an entomologist with the Illinois Natural History Survey, several graduate students, and I spent the afternoon in Menard County evaluating an experiment designed to test the efficacy of many insecticides and seed treatments against grape colaspis. We found many very small grape colaspis larvae, numerous white grubs, and an occasional wireworm. Many of the plants that had been injured were stunted and purple. An examination of the roots on stunted plants revealed that hairs on most roots had been pruned away completely. After we've had a chance to analyze our data, we'll pass along the results. |
David Quarles, technical service agronomist with Golden Harvest Seed Company, Hannibal, Missouri, passed along very similar observations from a grub-infested field near Hull, Illinois (Pike County). David indicated the colaspis larvae were only about one-eighth of an inch in length. This matches our observations of colaspis larvae in Menard County. Grape colaspis larvae, when full grown, can reach lengths of one-sixth of an inch. So, some feeding will continue to take place in producers' fields. For most of the Corn Belt, larval development will not be complete until mid-June to early July. Because we are running somewhat ahead this year on heat-unit accumulations, we may see larval development accelerated this spring. Typically, grape colaspis adults begin to emerge from cornfields in July.
Grape colaspis larvae at base of corn seedling.
Corn seedling injured by grape colaspis.
The observations from our research group and those of David Quarle's are very common this spring, especially in central and west-central counties of Illinois. Mild winters and early planting have aggravated the grub situation considerably this year. Look for results of our grape colaspis insecticide-efficacy trial in one of the upcoming issues of this Bulletin. We realize it's too late this spring for this information to be used; however, there's always next year.--Mike Gray