Soybean fields in many areas of Illinois continue to be "blessed" with bountiful densities of grape colaspis adults. We should not be surprised by these observations based on the extensive number of reports concerning grape colaspis larval injury earlier this summer. Silvia Rondon, a graduate student in the Department of Crop Sciences, continues to capture grape colaspis adults on Pherocon AM sticky traps in several crops, including oats, corn, soybeans, and alfalfa. Adults were most abundant in soybeans and alfalfa. Although Pherocon AM traps seem to work quite well in capturing grape colaspis adults, to date no economic threshold has been established for this insect pest. Keep in mind that, until recently, the grape colaspis was considered a secondary pest, not prone to cause economic losses in most years. As our readers know, this model has changed in recent years. |
If you're using Pherocon AM traps to monitor densities of western corn rootworm adults in your soybean fields, it may be a good idea to also keep track of the numbers of grape colaspis adults that are caught. Although we can't be certain that eggs will be laid in that soybean field, possibly setting the stage for root injury in rotated corn next spring, you will at least have some additional information to make a more informed management decision next spring. Grape colaspis adults on occasion can be confused with northern corn rootworm adults. Grape colaspis adults are tan and oval (1/6 inch in length) with wing covers that reveal tiny punctures. Northern corn rootworm adults are slightly larger (1/4 inch in length) and have smooth wing covers that are pale to dark green.--Mike Gray
Western (left) and northern (right) corn rootworm adults.
Grape colaspis adults, pinned specimens.