You Are Here: Management Updates 2006 Archive April 27, 2006

Date: April 27, 2006
Category: Insects
Subject: White Grubs

Grubs - what can you do?
Many people have been asking whether there is anything that can be done to manage grub damage that is occurring this spring. There are a couple of "traditional" insecticides that may provide some relief at this point in parts of New England, but in many cases, little is gained by treating in the spring. White grubs that are feeding now are nearly full sized, so it takes a higher level of exposure to a chemical to be effective than it does in later summer or early autumn. In addition, some of the grubs (especially European chafers) will stop feeding within the next four or five weeks. Meanwhile as they begin to slow their feeding, their physiology is changing so they are often less susceptible to insecticides.

Dave Shetlar, my colleague at Ohio State, indicates that spring applications of grub insecticides seldom provide more than 50% control. But for some turf managers, 50% may be "good enough", so the temptation is there for some people.

So here are the main points to keep in mind:

1. Only treat areas where you have monitored and confirmed the presence of grubs (or their $*^&^#* predators, like skunks or raccoons).

2. If you are going to treat grubs in the spring, you must use a fast-acting, relatively soluble product. The most consistent performer would be trichlorfon (Dylox™ or "Bayer Advanced 24- Hour Grub Control™), which will act within two or three days. (note that Dylox™ cannot be used on school properties that are under the mandates of the Children & Families Protection Act in Massachusetts, and is not labeled on turf in Maine. There may also be others of you in the "viewing area" that cannot use Dylox™ as well.) Also note that Dylox™ is very sensitive to pH and will break down very quickly when the water pH is above 7.5

2a. Carbaryl (normally sold as Sevin™) is another relatively fast-acting product that some people have used to treat spring grubs. Our experience has been that Sevin is very inconsistent. In addition it is very toxic to honey bees and other bees and wasps, so it should never be used when bees are foraging. And Sevin™ is also on the list of products that cannot be used on school properties that are under the jurisdiction of the Children & Families Protection Act in Massachusetts.

3. Imidacloprid (commonly sold as Merit™ but also available under several other trade names now) applied in the spring is not effective on grubs that are present in the spring. And because many turf managers in New England are dealing with some of the harder-to-control species of grubs (like European chafers and oriental beetles), I do not recommend that Merit™ be applied earlier than mid June. (The month of July is an even better target in most situations, especially on irrigated turf.)

4. We have not conducted any trials using entomopathogenic nematodes against grubs in the spring, and I have not seen any data to indicate whether those nematodes would be effective in spring conditions. Keep in mind that Steinernema carpocapsae, one of the more readily available species of nematodes, does not work on grubs. The one that would be most likely to work would be Heterorhabditis bacteriophora, but studies at Rutgers University (Albrecht Koppenhofer) suggest that the HB nematode is much more effective against Japanese beetles than other species of grubs. Since many of the turf managers in New England are dealing more with European chafers and oriental beetles now, it is unclear how effective the HB nematode will be in New England (white grub ID). The good news is that Dr. Koppenhofer has discovered a new species of nematode that looks extremely effective against all of our major grub species, and we are hopeful that the "new" nematode can be commercialized reasonably soon.

Again we do not know whether nematodes can be effective in the spring. At the very least, applications should be delayed until soil temperatures warm up a bit (perhaps to 55 to 60 degrees or so???). Nematodes are living organisms and are not nearly as effective when applied in cooler conditions.

5. If you decide to treat for the grubs you have in the spring, be sure to water in the application thoroughly - a minimum of 0.1 inch, and 0.25 inches is even better. Use even more water if you decide to use nematodes.

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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