You Are Here: Management Updates 2005 Archive August 16, 2005

Date: August 16, 2005
Category: Insects
Subject: White Grubs, Webworms

While much of our field time has been spent tracking down annual bluegrass weevils, we have been seeing eggs and tiny larvae of various grubs in our travels. So I thought I would provide a quick update on what seems to be going on.

In areas where soils have been unusually dry, I would expect that egg-laying of Japanese beetles, oriental beetles, asiatic garden beetles, and European chafers to be delayed. Adult females seek sites with "adequate" soil moisture, because the eggs are very vulnerable to desiccation. So in some locations where there was considerable rain early in the summer, some eggs would have been laid at that time. But since then, many areas in New England have been without rain for several weeks and the air temperatures have been unseasonably (and unreasonably!) high. So I would expect that female beetles are holding on to the rest of their eggs until conditions improve. This means we may see newly laid eggs as late as the last week of August or the first week of September.

Nevertheless, we have seen eggs and small larvae in a variety of turf settings, all within the last week or so. Clearly some grubs will be right on schedule, and feeding more and more on the turf roots.

Because there may be a delayed egg hatch, imidacloprid (Merit™) might still be effective at this point, particularly in northern New England. And remember that there is a new product out that is very similar to Merit™ chemically, but claims to have better activity against medium-sized larvae. That product, chlothianidin (Arena™) has looked excellent in our field trials when it was applied before eggs hatched, but we have not yet tested it for later season applications. (Note that while Arena™ received federal registration during the winter, each state must approve the product as well. I do not know the state registration status of Arena™ for each state.)

Meanwhile this would be an excellent time to apply halofenozide (Mach 2™) against Japanese beetle grubs, but it may be too late for European chafers. (Remember that Mach 2™ has been very inconsistent over the years on oriental beetle populations.) And because this has been such a dry period, Mach 2™ must be watered in, despite what the label might say. (In a previous dry year, we tested a variety of Mach 2™ treatments and withheld water from half those plots. When we returned in the fall to rate the products, the plots that had not received water after the application were essentially dead from grub feeding while the identical treatments that had been watered in were green and healthy.)

Webworms?
Just as a curiosity report, I saw literally hundreds of webworm adults flying just above my lawn the other night while I was mowing. There are several species of webworms that occur in New England. Normally we notice webworm activity in lawn turf, but the caterpillars rarely cause visible damage in such settings. However, they can also occur on golf courses and cause damage. Fortunately, the insecticides used against cutworms will also work against most webworms. This late in the season, I would not worry about them in most situations. The moths may lay eggs that will hatch into small caterpillars, but those caterpillars will not be feeding actively for another week or two, and by then we should be seeing a break in this hot weather.

Submitted by: Dr. Pat Vittum

DISCLAIMER - As always, it is the responsibility of the applicator to verify the registration status of any pesticide BEFORE applying it. Different states have different regulations as well. The author and the University of Massachusetts are not liable for any consequences of any pesticide "recommendations". Mention of any trade name is not to be considered endorsement of a product.

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