You Are Here: Management Updates 2006 Archive April 3, 2006

Date: April 3, 2006
Category: Insects
Subject: White Grubs

They're back!!!
It will come as no surprise to many of you that white grubs are returning to the root zones in New England even as I type. We found oriental beetle grubs and European chafer grubs feeding on the UMass Amherst campus last week, and with the recent warm temperatures, grubs are becoming active throughout southern New England.

Just a quick refresher - European chafers are spreading throughout New England and can be found in many parts of Massachusetts now. They are the most damaging species of annual white grubs (species that have one generation per year), in part because they are the largest species and in part because they are least sensitive to cold. In many areas the chafers have been feeding for a couple
weeks already. (And of course the European chafers tend to be the most difficult species to control.)

Regardless of species, any of the annual white grubs you notice this spring will feed until late May or early June before they pupate. Adult beetles will emerge in mid June (European chafers) to early July (Japanese beetles, oriental beetles, Asiatic garden beetles).

Grubs that are active in spring are difficult to control because they are quite large and their physiology is changing. Nevertheless, a quick acting insecticide such as trichlorfon (Dylox™) can provide some relief in some cases. While we do not have data on soil temperatures, we believe that spring insecticides should not be applied until soil temperatures (at two inches) have reached at least 50 degrees. So there is a very short window of opportunity between the time when soils are warm enough and the grubs stop feeding. If you do treat for spring grubs, remember to water in the application with at least 0.1 to 0.2 inches of irrigation (or rainfall).

Note that imidacloprid (Merit™) applied in the spring does not work on the grubs that are present in the spring. So do not be misled by the "season-long control" claim that can be found on some of the homeowner formulations of imidacloprid. Also, in New England applications of imidacloprid made as early as May might or might not still be active in July and August when our more challenging grub species are present. So unless you have a really good reason (and assuming that white grubs are your primary concern), delay imidacloprid applications until mid June to early August.

Finally, note that the two "curative" insecticides normally used against white grubs in the spring trichlorfon (Dylox™) and carbaryl (Sevin™) are both on the list of pesticides that cannot be used on school grounds that come under the auspices of the "Act Protecting Children and Families from Harmful Pesticides" in Massachusetts. For more information, go to the Massachusetts Department of Agricultural Resources website for the act: http://www.massnrc.org/ipm

This means that turf managers who are managing athletic fields on school grounds in Massachusetts have no insecticide options for controlling white grubs that damaged fields last fall or are damaging fields this spring. Insect-attacking nematodes might be considered by some to be an alternative, but research out of Rutgers University indicates that Heterorhabditis bacteriophora (a nematode that is commercially available and has some activity on grubs) is only effective against Japanese beetle grubs. In many areas of Massachusetts, the Japanese beetle has become secondary to European chafers and oriental beetles. And there is very little information on how effective nematodes are when applied in the spring, or what the soil temperature must be at the time of application.

Thus, the primary "option" for turf managers without access to Dylox™ or Sevin™ will be to manage the damage as much as possible. This may mean rolling fields before games to try and reduce slippage. And if your grub activity is significant this spring, make a note to apply imidacloprid during July to forestall similar problems this coming fall.

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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