You Are Here: Management Updates 2009 Archive August 14, 2009

Date: August 14, 2009
Category: Insects
Subject: White Grubs

As a result of the cool, wet weather of the summer, Japanese beetle adult activity has been slow to appear. But I have seen some pretty good flights of beetles in the last week or two - in the Amherst (MA) area and in central New Hampshire.

Normally European chafer grubs prefer drier locations, but we have not had many of those in most of New England. (Some golf courses have reported 18 inches of rain since 10 June.) Chafer adults appeared to be close to "on schedule" for emerging and laying eggs, but time will tell how well the grubs do in the wetter than normal soils.

Oriental beetle adults appeared to be close to "on schedule", first appearing in Amherst in the third and fourth week of June. But again, the steady wet weather may have caused females to delay egg laying.

Japanese beetle adults were at least a week or two behind normal on emergence. They are much more active on sunny days, and those have been few and far between until the last week, so many of the beetles have been biding their time, waiting for soils to dry out and for the sun to appear. They are busy laying eggs now.

In general watch for grub activity in areas that are usually high and dry. Because of the wet summer weather, many females are seeking drier areas to lay eggs. So don't just look in the usual places, but keep an eye on any areas that have drained well and have not retained moisture as much as other areas.

How has the wet weather affected insecticide applications?

I have had a couple of turf managers ask me whether the heavy rains of June and July would have washed any of the neonicotinoid applications out of the root zone. (The neonicotinoids include chlothianidin, available as Arena™ or in the combination product, Aloft™; Merit™ and the generic formulations of imidacloprid, as well as the combination product, Allectus™; and thiamethoxam, available as Meridian™).

I asked my Bayer representative, and he assured me that as long as the application was in place for at least a day or two before a drenching rain, the product should be just fine. Much of it would be absorbed into the roots within the first couple days, and should be available to control grubs later in the season.

Is it too late to use a neonicotinoid this year?

This is a tougher question. While the labels suggest that neonicotinoids are most effective if applied when beetles are laying eggs, there appears to be some field evidence that chlothianidin and thiamethoxam, at least, can be used a little later in the summer with good success. I would still try to have the applications completed by the end of next week (21 August) if at all possible. Remember that the neonicotinoids take five to twenty days to become active (depending on active ingredient and soil temperature), so the longer you wait, the larger the grubs will be when the active ingredient releases.

At least the soils have dried out enough in most locations so that you can water the application in!

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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