It's early in the growing season, but many people already have the sense that white grubs will be problematic again this year. Kevin Black, with Growmark in Bloomington, reported that many FS crop specialists have observed heavy infestations of white grubs heavy in many fields in southern Illinois. Kevin found Japanese beetle grubs in a couple of fields in Randolph County. In addition, several farmers from western and central counties have reported finding white grubs during their planting operations. The species of these grubs have not been identified, but their presence is worthy of note. Remember, as I indicated in issue no. 2 (April 5, 2002) of the Bulletin, both Japanese beetle grubs and Phyllophaga grubs (so-called true white grubs) are capable of causing significant economic damage. Cyclocephala grubs (masked chafer grubs) infrequently cause economic damage to corn. Once again I remind you to accurately identify the species of grubs you find. The information provided in issue no. 2 of the Bulletin will help you determine what type of grubs you have found.|
While reading an article written by Marlin Rice (Extension entomologist at Iowa State University), for Integrated Crop Management (issue no. 5, April 15, 2002, http://www.ipm.iastate.edu/ipm/icm/ 2002/4-15-2002/whitegrubs.html), I realized there was another type of grub I had not mentioned. Aphodius grubs, or manure grubs, may be found in fields that have received heavy applications of manure. Aphodius grubs are quite small (refer to Marlin's photograph), and they are almost U-shaped rather than C-shaped. The head is red-brown, rather than yellow-brown, like the other grubs discussed.
Corn plants injured by Japanese beetle grubs or Phyllophaga grubs may appear wilted or stunted, and the lower portion of the stems may appear purple (phosphorus deficiency). Heavy infestations of white grubs may cause severe stand reduction. In fields where corn plants have emerged, look for these symptoms first, but make certain you find the grubs before you blame them for the injury. Other factors can cause similar symptoms.
We would be interested in learning what types of grubs are being found throughout the state this year. Don't hesitate to contact me to let me know whether you have found Japanese beetle grubs, Phyllophaga grubs, Cyclocephala grubs, or even Aphodius grubs. We'd like to develop a "portrait" of white grub problems in Illinois. We need to learn as much as we can if we ever hope to be able to predict their occurrence.--Kevin Steffey