You Are Here: Management Updates 2007 Archive October 29, 2007

Date: October 29, 2007
Category: Insects
Subject: White Grubs

There has been some confusion about a recent posting of mine regarding the role of Milorganite™ and other similar products in managing secondary grub damage. As we all are well aware, sometimes the main problem with grub activity is the birds and four-legged "varmints" that forage in the area and feed on the grubs. As I have said so many times, these animals are excellent biological control agents because they are often very thorough at finding grubs and removing them, but they leave the area in total disarray.

Anyway, I mentioned that my colleague at Ohio State, Dave Shetlar, had reported that the use of Milorganite™ and similar products seemed to encourage skunks and some other animals to move on to other locations to forage. But I had a typographical error in that message that implied it was the grubs that were encouraged to move. So please note the error.

Now that we have finally had a sharp frost in many areas, and the temperatures look to be turning more seasonal, we can expect Japanese beetle grubs to start moving downward in the soil profile fairly soon. The European chafers, of course, are much less sensitive to cold and will continue to feed for a few more weeks in many locations.

Finally, for those of you looking to make inventory decisions for 2008, please note that we have not yet seen any evidence or heard any reports of white grubs developing resistance to imidacloprid (Merit™ and several generic products). This is in spite of the fact that turf managers have been using Merit™ for many years, sometimes treating the same areas year after year. Of course normally we recommend that turf managers avoid using insecticides in the same chemical class year after year, as a major "defense" against resistance. But as we have lost several turf insecticides in the past five years, we have been left with fewer and fewer alternatives and imidacloprid has been the "workhorse" as a preventive application.

So just to recap - imidacloprid is in the neonicotinoid class of insecticides. Two relatively new active ingredients (chlothianidin, sold as Arena™ and thiamethoxam, sold as Meridian™) are also in the same chemical class, so switching to them would not provide any protection against resistance issues.

Both of those "new" products claim activity against a wider range of turf insects, in part because they seem to have translaminar activity in the foliage after application. Note that a new combination product, chlothianidin plus bifenthrin, will be sold as Aloft™ in 2008 and appears to provide very good protection against many of the surface feeding insects, based on field results discussed at a recent workshop.

We still need to refine our understanding of the best time to apply such products. In much of New England, where the European chafer or oriental beetle is the primary grub species, early applications may lose their effectiveness against those species, but we still need to conduct some more field trials before we will have a solid understanding of "how early is too early?" I personally would suggest avoiding applications earlier than early June if grubs are the primary target, but we will be in a better position to understand the limitations after next year's field trials.

Submitted by: Dr. Pat Vittum

DISCLAIMER - As always, it is the responsibility of the applicator to verify the registration status of any pesticide BEFORE applying it. Different states have different regulations as well. Trade names of materials are provided for informational purposes only and do not substitute for a thorough and careful reading of the label and application according to label instructions. The author and the University of Massachusetts are not liable for any consequences of any pesticide recommendations. Mention of any trade name is not to be considered endorsement of a product.

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