You Are Here: Management Updates 2004 Archive August 2, 2004

Date: August 2, 2004
Category: Insects
Subject: More Confusion with Grubs

In recent updates, I have tried to describe the management options as I see them for white grubs in turf. The confusion arises when we are reminded that we have readers from all over the U.S. and Canada. Of course the pesticide regulations vary widely from one state or province to another. Further confusion arises for people dealing with mixed populations of white grubs.

Here is an attempt to further clarify some of the points I have been making over the past two or three months.

1. The number of turf insecticides labeled for use against white grubs is declining steadily. By the end of 2004, we will functionally be down to four or five standard insecticides in the United States - fewer than that in states or jurisdictions that have further restrictions. The active ingredients most often used for grubs in New England right now include halofenozide (Mach 2™), imidacloprid (Merit™), and trichlorfon (Dylox™). The first two are relatively slow acting and are most commonly used in preventive applications. (In some field trials halofenozide shows some curative activity against some species of white grubs, particularly when an application is made just as the young grubs are molting from the first instar to the second instar, but in general it appears to be a bit more consistent when applied just as eggs are hatching.) Dylox™, of course, is a very fast acting but short-lived product. (Note, again, that Dylox™ is on the list of products that cannot be used on school grounds in Massachusetts.)

In addition some turf managers in some states still have access to bendiocarb (Turcam™) or isofenphos (Oftanol™), but functionally those products are already gone. While the label is being supported through the end of 2004 in several states, product availability is very limited. Similarly, diazinon is being phased out of use around homes, and will not be available after 2004. Finally, as mentioned in a recent posting, some formulations of carbarly (Sevin™) are also labeled for grubs. Our experience has been that carbaryl is very inconsistent, but when it works, it works reasonably quickly (usually within five to seven days after application).

2. Different species of white grubs respond to insecticide applications very differently:

Oriental beetles are much less vulnerable to halofenozide than are other species of grubs. In general oriental beetles are less sensitive to many turf insecticides but the trend is most noticeable with halofenozide.

Japanese beetles are the easiest of the four New England species to control, and are quite vulnerable to halofenozide, imidacloprid, and trichlorfon. As long as the timing of the application is appropriate and the material is watered in, turf managers should achieve very acceptable levels of control.

European chafers fall somewhere in between. Field trials using imidacloprid or halofenozide against European chafers have provided a wide range of results. In field trials conducted in Massachusetts the level of control has ranged from less than 20% (usually with applications that were made in May or June) to nearly 100% control with both products, at one time or another. In general imidacloprid provides slightly higher levels of control than does halofenozide against European chafers, but these differences usually are not statistically significant.

One of the keys to achieving good control of European chafer grubs is to remember that the chafer life cycle is about two weeks earlier than the life cycle for Japanese beetles. The "application window" for halofenozide or imidacloprid is probably a bit shorter than the manufacturers tend to suggest, and the application must be watered in.

In any case, some of the text in an earlier message implied that halofenozide was not very active against European chafer grubs. In fact, if the material is applied at the right time and watered in, it can indeed provide very acceptable levels of control. To be absolutely thorough, I was in error when I wrote that my colleague, Steve Alm (URI) reported that halofenozide was not effective against European chafers. In a recent phone conversation, he pointed out that he has never made that observation. He (along with several other turf entomologists) has noted that halofenozide normally does not work on oriental beetles.

This is yet another example of why it is absolutely critical to identify the species of grub before making any management decisions.

Asiatic garden beetles are still more of a curiosity than anything else in New England, but their numbers appear to be increasing in some areas, particularly in unirrigated or poorly maintained turf settings. They are essentially untouched by imidacloprid - which may be why their numbers are increasing.

3. Note that the application window has probably already closed for imidacloprid against European chafers in southern New England, and it will be closed very soon for the other species as well. As always, grubs develop more slowly in northern New England, so imidacloprid applications can be made a little later in the summer.

- Submitted by: Dr. Pat Vittum