You Are Here: Management Updates 2004 Archive July 15, 2004

Date: July 15, 2004
Category: Insects
Subject: White Grubs

We are getting into the time of year when various species of white grubs are becoming active throughout southern New England. Japanese beetle adults are becoming very noticeable in many locations. Note that some of these beetles have small white spots on the thorax. These are eggs of a parasitic fly that will hatch into larvae and burrow through the exoskeleton, and destroy the tissue, eventually killing the adult. Do not kill these beetles ... the parasitic fly will take care of that for you!

European chafer adults have been "out and about" for at least a couple weeks and have begun to lay eggs. In addition we saw several oriental beetle eggs in soil samples from Westchester County, just north of NewYork City. The samples were taken late last week (9 July).

So... now is the time to review your plans for grub control. If you plan to use a slow acting product, such as imidacloprid (often sold as Merit™) and your primary target is European chafers, the product should be applied very soon - preferably by 25 July in most locations in Massachusetts. If you are targeting Japanese beetles or oriental beetles, the material should be applied by 10 August. In any case, it must be watered in with at least 0.1 inch of irrigation or rain. More water is even more helpful.

Halofenozide, often sold as Mach 2™, is also a relatively slow acting product but must be in place before grubs reach their third, and largest, stage of development. Studies in several locations indicate that Mach 2™ tends to be less effective against oriental beetles and European chafers than it is against Japanese beetles. Timing of application becomes even more important. Follow the guidelines given above for Merit™, and Mach 2™ will have a reasonably good chance to reduce grub populations significantly. (Note however that Steve Alm, an entomologist at the University of Rhode Island, has reported that Mach 2™ is much less effective against oriental beetles and European chafers, and he generally is not comfortable recommending it for those species. This is one of those "let the buyer beware" situations.)

A visit to the ubiquitous large general stores that abound (such as Wal-Mart and Home Depot) reveals that the shelves are full of granular insecticides with pictures of grubs on the label. Unfortunately, you must read the fine print and make wise selections. Most of the products that contain a pyrethroid as the primary active ingredient will not work against grubs because the product will be tied up in the thatch and never get to the soil. While there is a dizzying array of trade names, the active ingredients of pyrethroids include such things as: permethrin, cyfluthrin, bifenthrin, lambda-cyhalothrin, and deltamethrin. So take the time to look at the fine print.

Two other granular products appear on the shelves as well that can provide control of various white grubs if used properly. Carbaryl (usually sold as Sevin™) has been inconsistent in our trials over the years, but sometimes it works very well. It takes about five days to start working, and will remain active for about four or five weeks. So it should not be applied until most eggs have hatched - probably mid August for most locations.

Trichlorfon, often sold as Dylox™, is even faster acting but only lasts for seven to ten days. It should not be used until even later in the summer - late August or early September. Remember that Dylox™ is one of the products on the list that cannot be used on school grounds.

For those who want to use entomopathogenic nematodes, please refer to earlier posts on the subject, both in 2004 and 2003. Studies at Rutgers University in New Jersey indicate that the currently available nematode that works on grubs (Heterorhabditis bacteriophora) is quite effective against Japanese beetles but markedly less effective against other species. In any case, nematodes should not be applied until grubs have hatched out of the eggs and are beginning to grow. Water is even more important following nematode applications than for traditional insecticide applications.

- Submitted by: Dr. Pat Vittum