You Are Here: Management Updates 2003 Archive September 15, 2003

Date: September 15, 2003
Category: Insects
Subject: White Grubs

White grubs are a bit behind in their normal development in most areas of New England. Normally most European chafer grubs would be in their third (and largest) instar by now, and many of the Japanese beetles would be molting to their largest stage at this point. But field reports and personal observation confirm that grubs are running about a week or two behind "normal".

Dave Shetlar, my colleague in Ohio, reports that only 30% of the northern masked chafers have reached their full size. Jennifer Grant (Cornell University) reported seeing mostly second instar Japanese beetles in central New York a week ago. (In both cases, this indicates development is about a week behind normal.) Our own sampling in Waltham revealed first and second instars of European chafers, oriental beetles, and asiatic garden beetles. That is one or two weeks behind schedule.

Now would be a very good time to take a look. Even though you may not have seen any damage from the grubs feeding, or more likely from the skunks or raccoons that like to dine on the grubs, they may be well established. Because of the wet conditions that predominated through much of the summer in many locations, some grub populations may appear in areas that are usually a little too dry for grubs to thrive.

It is getting too late to treat for white grub populations this year. I suspect trichlorfon (Dylox™) applications would work through the end of September in most situatioins, unless we shift into an unseasonably cool weather pattern. But trichlorfon is the only traditional insecticide that would provide relief at this point. (Remember that turf managers who are responsible for school grounds in Massachusetts cannot use trichlorfon. Also trichlorfon is not legal in Maine under any circumstances. There may be other restrictions in other states of which I am not aware, so as always check with your local regulators before making an application.)

I do not know how late in the season an application of entomopathogenic nematodes can be effective. The latest we have treated an area with nematodes was the first week of September. (As it happens, we had very good control of Japanese beetles in that test.) Because the nematodes work reasonably quickly (assuming you use the right ones - see the archived grub messages from late April for information), they might be effective as long as the soil temperatures remain above 60 or 62° F (at two inches), but this is strictly a guess on my part.

- Submitted by: Dr. Pat Vittum