You Are Here: Management Updates 1999 Archive August 13, 1999

Date: August 13, 1999
Category: Insects
Subject: White Grubs

The temperatures have moderated and some areas have received rainfall (although not enough!), but still the dry conditions dominate insect activity. Keep in mind that European chafer grubs prefer dry areas, so even the most parched areas in eastern Massachusetts are at risk for grub damage.

My lab folks were sampling for grubs on a golf course in Berkshire County on Monday (9 August) and found large numbers of Japanese beetle grubs, ranging from eggs to small third instars. One cup cutter plug had 16 grubs in it - that would translate to 160 grubs per square foot!!! This particular location has received rain from several thunderstorms so is not in the drought condition so many are experiencing, but I report the results simply to provide a "heads up" that grubs are becoming active.

In drier locations grub activity may be delayed - beetles may have delayed egg laying, which would translate into delayed hatch.

Treatment options for grubs - for most turf managers in southern New England, it is getting too late to apply Merit to control grubs. Remember that it is a slow acting material, and often takes two or three weeks to start working. If at least half of your population is already second instars (middle sized grubs), you may want to consider a faster acting material.

The Mach 2 label says it can be used "curatively" (i.e., after grubs show up). Most of our field trials have tested Mach 2 as a preventive application, so I cannot comment directly on the curative action of Mach 2, but I would urge those who plan to use it to apply it before grubs have molted to the third (and largest) stage. In some areas (particularly places where European chafers are active), grubs are already showing up in that large stage, so in my mind it is nearly too late to use Mach 2. Also remember that Mach 2 is not as effective against oriental beetles and European chafers.

And as always - WATER WATER WATER. Good luck finding that water, but it is critical to successful grub control.

- Submitted by: Dr. Pat Vittum