Issue No. 12, Article 3/June 15, 2007
Japanese Beetle Numbers in Southern Illinois Are Already Alarming
Ron Hines, FS seed agronomist for Growmark's southern region, is already reporting that very large numbers of Japanese beetles are being captured in traps in southern Illinois. The trap in Massac County captured 15,645 Japanese beetles during the week ending June 12, an average of more than 4,700 per day. Captures of Japanese beetle adults for that week also are notable at the sites in Fayette County (816), the northernmost site; Jefferson County (578); Pope County (3,231), and Pulaski County (467). These large captures are tracking 1 to 2 weeks earlier than corresponding captures in 2006, so look out. (You can read Ron's comments at www.ipm.uiuc.edu/pubs/hines_report/comments.html.)
Some corn in deep southern Illinois is almost ready to tassel, and many Japanese beetles can be found in the whorls. As the tassels emerge, the Japanese beetles will move first to the tassels and then to the silks shortly thereafter. Obviously, the big concern with Japanese beetles in corn is their propensity to clip silks. The operating threshold is 3 beetles per ear, although we have stated frequently that we are not certain whether this threshold, developed from research conducted many years ago, holds up with modern corn hybrids, yields, and so on--so use your best judgment. We also have included comments indicating that silks must be clipped to less than 1/2 inch in length before pollination is compromised. Well, this may or may not be true, depending on many factors, including weather. Some people have observed that when hot, dry weather slows silk growth, the 1/2-inch guideline is not reliable and that 1 inch of silks is necessary. So, again, use your best judgment, especially if corn growth is negatively influenced by weather conditions.
And don't forget to watch for Japanese beetles entering soybean fields and chewing up the leaves, an especially critical concern when soybeans begin to flower. And don't forget to watch for Japanese beetles feeding on . . . well, you know the drill--they feed on more than 300 species of plants, including lots of fruits and ornamental plants. So brace yourselves; we could be in for another big year with Japanese beetles.--Kevin Steffey