John Wiley & Sons, Ltd.

Effects of formulation on transport of pyrethroids in residential settings

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Washoff of 17 pyrethroid products resulting from a 1 hour, 25.4 mm rainfall occurring 24 hours after application was measured in indoor studies with concrete slabs. These products included different pyrethroid active ingredients and a range of formulation types. Based on this replicated study, 5 product pairs with contrasting washoff behaviors were chosen for an outdoor study using 6 full‐scale house fronts in central California. Products in four of these pairs were applied once to different rectangular areas on the driveway (one product in each pair to three house lots and the other to the remaining three house lots). The products in the fifth pair were applied three times at 2 month intervals to vertical stucco walls above the driveway. All house lots received natural and simulated rainfall over 7 months. Indoor studies showed differences up to 170‐fold between paired products, while the maximum difference between paired products in the field was only 5‐fold. In the pair applied to the wall, one product had 91 times the washoff of the other in the indoor study while in the field, the same product had 15% lower washoff. These results show that, while the formulation may influence washoff under actual use conditions, its influence is complex and is not always as predicted by indoor experiments. Because formulation also affects insect control, washoff research needs to be conducted together with efficacy testing. This article is protected by copyright. All rights reserved

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