You Are Here: Management Updates 2008 Archive April 15, 2008

Date: April 15, 2008
Category: Insects
Subject: Spring White Grubs

After a long winter with seemingly interminable snow, spring finally seems to be making its way into New England. Trees are beginning to bud, daffodils are beginning to show (at least in the warmer spots!), robins are chirping ... but of course that means the white grubs will not be far behind.

For those of you dealing with European chafers, you are already seeing grubs back in the root zone feeding actively. As the frost leaves the soil, the other species will be feeding again very soon as well. So I feel duty bound to discuss your options for controlling white grubs in the spring.

Your best bet, if you need to reduce grub populations in the spring, is to use trichlorfon (Dylox™). But you will need to play a waiting game at this point and delay application until soil temperatures are 55° F or higher. Remember that trichlorfon is sensitive to high pH, so if you are using a sprayable formulation, check the pH in the tank and amend it if necessary. Also remember that trichlorfon cannot be used on school grounds in Massachusetts (and is also restricted in where it can be used in several other states beyond our "listening" area).

According to Dr. Albrecht Koppenhofer (Rutgers University), entomopathogenic nematodes are much less effective against spring grubs so you might save those products until young grubs are just hatching and becoming active in August.

There are three insecticides in the neonicotinoid group that are now labeled for use in turfgrass: imidacloprid (recently went off patent but most familiar as Merit™); chlothianidin (Arena™); and thiamethoxam (Meridian™). In addition there are two products that combine a neonicotinoid with a pyrethroid: Allectus™ (Merit™ plus Talstar™) and Aloft™ (Arena™ plus a generic form of bifenthrin).

Some of these products are positioning themselves to provide "season long control", which of course implies that a spring application of the product would control white grubs that are present in the spring. But field trials conducted in several states have shown that spring applications of these materials normally do not control spring white grubs.

In areas of the country where the primary grub species is Japanese beetle or masked chafer, spring (April or May) applications normally are still active enough to control the grubs of those species as they begin to emerge in July. Those early applications, especially of the combination products, no doubt would do a very good job of controlling, or at least suppressing, several other turf insects in a lawn-type setting - things such as chinchbugs, billbugs, or caterpillars - throughout the summer.

But in New England, where our primary grub species are European chafers and oriental beetles, there may be times when we need to avoid the temptation to apply a neonicotinoid (whether alone or in a combination with a pyrethroid) too early. I believe we run the risk of seeing a decline in performance against our European chafers and oriental beetles if we apply those products earlier than early June. Sometimes those "early" applications will hold and work fine in August, but I believe there are times when they will not.

So the bottom line is - if you have grub problems showing up now, either manage the damage (eliminate the rummaging four-legged varmints somehow!) or use trichlorfon to clean up the area. Do not use a neonicotinoid yet - it will not touch the grubs you see right now.

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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