You Are Here: Management Updates 2008 Archive July 30, 2008

Date: July 30, 2008
Category: Insects
Subject: Insecticide Efficacy Influenced By Rainfall

What effect has the heavy rain had on recent insecticide applications?
Much of New England has been subjected to persistent heavy rain over the past ten days. Several areas have had six to ten inches of rain in the last week. Several golf course superintendents have asked me whether the heavy rain has moved insecticides too deep into the soil to be effective against turf insects - or has resulted in surface run-off.

According to a field representative from Bayer Crop Science, the key points regarding the effect of rain on applications of Merit™ (imidacloprid) are: how much time elapsed between the application and the onset of rain, and how much organic matter is in the soil. According to my source, as long as the application was not made immediately before the beginning of the downpours, much of the product should have been taken into the plant or bound to soil before the rains came. In addition, as long as there is some organic matter in the soil, some of the product should be bound to that organic matter, which would slow the rate at which it would move through the soil profile. So if applications were made to very sandy soils, they may have "disappeared", but applications to other more loamy soils should be OK.

I have not yet asked the tech reps from Valent or Syngenta about the effect of the rain on applications of the other neonicotinoids, thiamethoxam (Meridian™) and chlothianidin (Arena™). They are usually described as being a little more soluble than Meri™t, so one would think they might be a little more likely to run-off following very heavy rain. But the solubility also enables the product to be taken up into the plant more quickly, so as long as there were a few hours between the application and the onset of rain, you should be OK.

Meanwhile the rain probably had little effect on applications of pyrethroids, because they are virtually insoluble in water and therefore much less mobile than other insecticides. The converse is that applications of carbaryl (Sevin™) or trichlorfon (Dylox™) are undoubtedly gone. They are the most soluble turf insecticides on the market and would not have been able to withstand the onslaught of water!

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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