QUESTION:
According to Cornell, Michigan State, Oregon State and our own U.C. Davis under info quoted in their “Environmental Fate” paragraph on Pyrethroids they state that “Bifenthrin does NOT move in soils with large amounts of organic matter, clay and silt. It has low mobility in sandy soils that are low in organic matter. Bifenthrin is relatively insoluble in water, so there are no concerns about ground water contamination through leaching.” From the Calif. Dept. of Pesticide Regulation we are told “Since water is polar, Bifenthrin has a low solubility and correspondingly strong tendency to bind to soil”.
I’m a bit puzzled then, as to why the dramatic label issues regarding pyrethroids.
ANSWER:
I agree that it is frustrating each time we have tools or some of their uses taken from us in pest management. But, I have to recognize that this is inevitable and will always happen as our government and our country make the effort to move to lower use of toxic substances. I think overall this is a good thing to try to accomplish, and if we can provide the same quality of needed pest management with less use of toxic substances that should be our goal and our role. In the case of the new restrictive wording on synthetic pyrethroids most of the statements seem to be fairly reasonable, and if they were based on good science and accurate conclusions then perhaps it is a good thing that we now must use them in a manner that reduces the chances for these active ingredients to move off site.
I agree that pyrethroids have very low ability to move once they are in the soil, and this is probably why our uses of them on turf and soils around landscape as well as on trees and shrubs is not changing. It is recognized that applying them to dirt or foliage will not be likely to result in movement off site, unless, as the new Label statements now tell us, that soil is already saturated or frozen, in which case the material applied on top of that soil would not have the opportunity to soak in and bind to the soil particles. So, with the new labeling our uses on bare soils and turf have not changed.
What HAS changed is our applications to “impervious” surfaces where the active ingredient does NOT have the opportunity to bind to soil particles, and now may sit there on that concrete or wood deck until rainfall or excessive irrigation removes it and allows the pyrethroid to flow with the water down the driveway, into the gutter, and to the local creek. The same goes for applications to wide expanses of exterior walls – the pyrethroid active ingredient is likely to be sitting there for rainfall against that wall to move it off site. Perhaps we should feel fortunate that we still are permitted to apply “spot” and C&C applications to exterior, exposed surfaces, as this allows us to continue to treat for most pests in an effective manner.
We could probably make an argument that pyrethroids applied to most impervious surfaces around homes would most likely end up on the nearby turf or soils even if they were washed off that sidewalk or patio by rain or sprinklers. But, that would always be an unknown with too many variables, and leaving it up to the discretion of the applicator could very well result in too many bad decisions made for the purpose of expediency and “getting the job done” quickly.
So, I think your statements are all quite accurate and that this information was taken into consideration when the new Pyrethroid label restrictions were written, and this is why we did not have additional restrictions on uses on turf and ornamentals or on bare soils. The only place this is addressed, perhaps, is with respect to granular applications on turf or in landscape, where the applicator is required to sweep all material back onto the turf or soil if it lands outside that intended target site, perhaps on the sidewalk. I think you and I have both seen some really sloppy applications of insecticide granules over the years, with granules ending up (as I have seen) on cars, sidewalks, and once in the food bowl of household pets where that bowl was on the wood deck near the back door.
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