You Are Here: Management Updates 2003 Archive May 29, 2003

Date: May 29, 2003
Category: Insects
Subject: White Grubs, Annual Bluegrass (Hyperodes) Weevil

White grubs: We continue to receive telephone calls and e-mail inquiries about white grubs. Most of the species are beginning to slow their feeding, and it does not pay to attempt to control grub populations at this point. European chafers will be done feeding within the next week or two (and then will prepare to pupate by eliminating any food stored in their digestive system). The pupa stage will last for about ten days, in the upper inch or two of the soil, and new adults will emerge between the middle and end of June. Japanese beetles and oriental beetles will be a week or so later in pupating and emerging as beetles. The main point is that trichlorfon (Dylox), the only fast-acting grub material currently on the market, will not be effective against these late-stage grubs, in part because the grub physiology has already changed significantly and the grubs will not be nearly as susceptible as they are in late summer or early spring.

Annual bluegrass (Hyperodes) weevils (golf course only): During a conference call with some of the Cornell University turf folks this morning, I learned that Cornell staff people have observed annual bluegrass weevil eggs and larvae in turf samples from Long Island. The question is, "What has this prolonged wet and cool spring done to weevil development?"

My own guess is that the normal oviposition period (which normally begins shortly after Forsythia reaches full bloom) was much longer than usual, and I suspect we had a very extended period of egg-laying. In fact in some areas dogwood was in full "bloom" for a couple weeks or longer.

This means we may not see the tidy peak in larval activity that often occurs in June. In other words, we often see a one or two week period when damage is significant and then most of the weevils have moved on to become adults and start the second generation. I expect it will be harder than usual to figure out what is going on this summer, and there will be even more overlap of generations than usual.

The short prediction - I suspect we will see "only" three generations in Westchester County and the rest of the metropolitan area this year, but it will be nearly impossible to determine where the population is (in terms of stage of development) for most of the year. We will find eggs, small larvae, medium larvae, large larvae, pupae, and adults in virtually any sample we take.

For those in the metropolitan area who jumped the gun and treated at Forsythia full bloom this spring, you should watch for larval activity in the next week or two. If you see the tell-tale wilting (which sometimes resembles foliar anthracnose), check to see whether you see any larvae feeding in the crowns. One cultural suggestion - based on Nikki Rothwell's recently completed Ph. D. field studies, we are thinking that nutrient levels may be one aspect of the total picture. If nitrogen levels drop too low, weevil feeding may be much more obvious. So pay attention to the "spoon feeding", and try to avoid staying too "lean and mean", especially during the peak damage period. Again, I expect damage to become apparent in the metropolitan area within the next week to 10 days, and slightly later in central New England.

Good luck!

- Submitted by: Dr. Pat Vittum