You Are Here: Management Updates 2007 Archive October 5, 2007

Date: October 5, 2007
Category: Insects
Subject: White Grubs

It appears to be a banner year for white grubs! We have seen damage at levels I had not observed in several years - large areas torn apart by skunks or raccoons scavenging for the grubs. Damage has been significant throughout the state, and all three major species (European chafers, Japanese beetles, and oriental beetles) have been very active.

As the saying goes, "hindsight is 20 - 20", so here is what I think happened: The dry weather of August forced some beetles to delay laying eggs because they could sense that the soil moisture was very low at that time and the eggs would not survive in the dry soil. So we saw lots of very small grubs in late August and early September, more so than usual. We did not see much damage at that point because many of the grubs were still pretty little.

Then as the "late" grubs matured and joined their brothers and sisters who had developed "on schedule", the numbers of large grubs exceeded threshold levels pretty quickly. And meanwhile of course, most areas have not received much rain in September, so there has been little moisture available to mask the damage.

For many of you, the main problem now is dealing with the secondary damage - the critters (skunks, raccoons, crows, starlings) that are dining on the grubs. As I have said so many times, they provide excellent biological control because there are very few grubs left in the areas where they forage, but we have never been able to teach them to "put the grass back".

My counterpart in Ohio, Dr. Dave Shetlar, suggests that Milorganite™ applied to the surface in areas where skunk activity is greatest can convince the grubs to move on to other locations. That may or may not be a good thing, depending on where they go! I do not have personal experience with this approach but am passing it along to offer an alternative to those of you who are really struggling with grubs right now.

Ordinarily early October would be too late to apply a curative product such as trichlorfon (Dylox™). But with air and soil temperatures so unseasonably mild this year, you might get some relief. This is not a recommendation because the date is so much later than usual.

If you do decide to apply trichlorfon, do it before the weather turns colder and remember:

1. Trichlorfon cannot be used on school grounds in Massachusetts (and is subject to similar restrictions in some other states as well.)
   
2. Trichlorfon must be watered in - with at least 0.25 inch of water this late in the season, especially because the soils are so dry. (Even more irrigation would be even better).
   
3. Trichlorfon is sensitive to rapid breakdown in water with high pH, so if your water supply has a pH above 7.0 to 7.2, plan to use a buffering agent to reduce that sensitivity.

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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