You Are Here: Management Updates 2001 Archive September 5, 2001

Date: September 5, 2001
Category: Insects
Subject: Monitoring White Grubs

We are getting several calls from people who are seeing damage from white grubs, and yet the turf manager did not notice much Japanese beetle activity during the summer. In some cases I suspect the "guilty" grub species may be the European chafer, because the adults of that species are night fliers and less likely to be noticed. Meanwhile there are other locations where the grubs are all Japanese beetles, and there was little noticeable adult activity earlier in the summer. So just because you did not see many Japanese beetle adults flying earlier this year does NOT mean you can count on having a quiet grub season.

If you did not use imidacloprid (Merit™ among others) or halofenozide (Mach 2™ among others) earlier in the year, and you are just discovering that you have grub activity, you can consider using one of the quicker acting materials, like bendiocarb (Turcam™) or trichlorfon (Dylox™). Turcam takes three to seven days to start working, so if you are going to use it, plan to make the applications no later than 10 September. Dylox works more quickly, and grubs will be affected as quickly as one or two days after application, so treatments normally can be delayed as late as 20 September (and possibly even later).

If you used Turcam within the past week and are wondering whether it is going to work for you, go back to the treated areas and collect a few of the grubs. Study them carefully - the first sign that an insecticide is killing a grub is a very subtle color change. The body begins to turn a pale yellow or honey color, often most noticeably right behind the head. In addition, affected grubs are much less active - their legs will not wriggle as much, the body is less firm.

The color change will begin to become apparent about four to seven days after an application of a material like Turcam, and then the grub begins to decline rapidly. If most of the grubs you inspect are showing the color change or are beginning to look a little piqued, you can figure the application is working and the grubs are "on the way out". If the grubs still look healthy (gray color along the back or tail, steady creamy color, active legs, firm or turgid body) and it has been at least a week since you treated, you may need to make a follow-up application with Dylox.

As always, whatever action you take, YOU MUST WATER THE INSECTICIDE IN. And keep in mind that a few grubs in an area will not lead to major turf damage. ONLY USE AN INSECTICIDE IN AREAS WHERE GRUB POPULATIONS EXCEED TOLERANCE LEVELS. (Those levels vary with species, and are lowest for European chafers, highest for asiatic garden beetles.)

- Submitted by: Dr. Pat Vittum