You Are Here: Management Updates 2005 Archive July 20, 2005

Date: July 20, 2005
Category: Insects
Subject: Soil Moisture & Grub Control

Yesterday I wrote about the importance of delaying applications of grub insecticides if soils are saturated. In my provincial way, I figured everyone in New England was as wet as we are here in western Massachusetts. (I measured 7.25 inches of rain in a six day period at my house just north of Amherst. It fell as 2.35, 0.9, and 4.0 inches, at two day intervals, with the last "dump" on Monday afternoon.) Needless to say, our soils are still saturated and will be for a few more days.

Anyway, I have been reminded ever so gently by several folks that conditions are variable and there are places in southeastern Massachusetts, among others, that are very dry.

If soils are very dry, beetles may delay their egg-laying for one to three weeks. This means that grubs are delayed in their development and damage is masked until well into September. By then it sometimes is too late to do anything. So monitoring is even more important this summer - look for the pearly white eggs in the soil (one to three inches below the surface), and look for tiny grubs in the upper part of the root zone or lower thatch.

If soils are so dry, coupled with high temperatures, that the turf has gone dormant, it is even more important to water in the insecticide. Keep in mind that imidacloprid (Merit™) has systemic qualities and is absorbed by the roots, so it can be harder to get it to the right target when turf is dormant because roots are not actively taking up water.

If water is available and soils are very dry, studies indicate you will benefit by irrigating the area about 24 to 36 hours before you treat (with at least 0.2 inches of water), and then following the application with at least 0.1 inch of irrigation. The reason this seems to help is that grubs naturally migrate down in the soil profile when soils are hot or dry. The pre-treatment irrigation tricks the grubs into thinking conditions are improving in the root zone and they migrate upward, where they get an unpleasant surprise.

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. 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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