You Are Here: Management Updates 2002 Archive July 1, 2002

Date: July 1, 2002
Category: Insects
Subject: Frequently Asked Questions - Grubs in July

Many turf managers are calling or e-mailing with questions about insecticide options for white grubs in New England. Here are some of my quick responses to those questions.

Note that there are several trade names for the two active ingredients discussed here. Halofenozide is most commonly known as Mach 2, while imidacloprid is the common name for Merit (among other trade names).

Should we be treating during this very hot weather?

In many cases I think you are better off delaying applications until we get a break in the temperatures. The turf is already under stress and if you have the option you might delay until highs are in the low 80s and humidity has dropped. The materials that are currently available will work well on most grub species as long as they are applied in early to mid July. (See below.) Furthermore, it is really difficult to get adequate water on the treated area when air temperatures are so high. Much of the water evaporates before it has a chance to "move" the material.

What is the absolute best time to apply Merit or Mach 2 in Southern New England?

Most turf managers in southern New England (Connecticut, Rhode Island, and much of Massachusetts) are dealing with oriental beetles and/or European chafers. If either of those species is the primary species in your location, you probably should try to get product down by the end of the third week of July (19 July) if at all possible. However, it is absolutely essential to water the product in. If we do not get much rain during the next three weeks, it is probably better to delay the application a little bit until there is adequate rainfall, but try and have the product in place no later than 26 July. If you have an adequate supply of water for irrigation, aim to have the product in place by 19 July.

If the primary grub species is the Japanese beetle, your target dates for application should be about two weeks later.

I am hearing conflicting reports about halofenozide (Mach 2). Can it work against oriental beetles and European chafers in Southern New England?

Our field trials indicate that it is possible to get acceptable levels of control of oriental beetles or European chafers with halofenozide. However, both species are much more challenging than Japanese beetles so pay attention to details. (In general we see slightly lower rates of effectiveness for halofenozide compared imidacloprid, but if you have been using Merit-type compounds for several consecutive years, you may want to consider switching to halofenozide, which has a totally different mode of action.)

First, the TIMING of application is important. Be sure not to delay (see above) the application unless post-application water is an issue. And be sure to water in thoroughly - at least 0.1 inch, and more is even better.

Second, note that the new labels for many formulations of halofenozide include a higher application rate (2 lb ai per acre) for European chafers and oriental beetles. (The former rate, still appropriate for Japanese beetles, is 1.5 lb ai per acre.) Be sure to use the higher rate in areas where the challenging species predominate.

Finally, remember that no turf insecticide will provide 100% control of a grub population (even the more "wimpy" Japanese beetles). So don't expect miracles - be reasonable with your expectations.

- Submitted by: Dr. Pat Vittum