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(19-10) Toxicity Of Dormant Spray Pesticide Runoff From California Orchards: Ground Covers and Temporal Patterns . Werner, Inge*,1, Deanovic, Linda1, Henderson, John1, Wilson, Barry1, Wallender, Wes1, Krueger, William1, Oliver, Mike1, Zalom, Frank1, 1 University of California, Davis, CA ABSTRACT- Organophosphorous (OP) insecticides, especially diazinon and chlorpyrifos, have been routinely detected in surface waters of the Sacramento and San Joaquin River watersheds, coincident with storm events following their application to dormant orchards during the winter months. Preventive best management practices (BMP) aim at reducing pesticide runoff into surface waters. For example, OP pesticides are increasingly replaced by more hydrophobic pyrethroid pesticides such as esfenvalerate (Asana). In addition, various types of ground cover vegetation are believed to increase the soil's capacity for water infiltration, thus preventing storm runoff from orchards. To measure the effectiveness of these BMPs, storm runoff was collected in a California prune orchard (Glenn County, CA) during several subsequent rain storms in the winter of 2001, after two insecticides (diazinon, esfenvalerate) were applied to different orchard sections. Bare soil and 3 different cover crops were tested for their effect on runoff and toxicity to standard bioassay and California resident species. Acute toxicity was tested by exposing larval fathead minnows (Pimephales promelas), larval rainbow trout (Oncorhynchus mykiss), and two cladocera species (Ceriodaphnia dubia, Simocephalus vetelus) to runoff water samples. Mortality was recorded after 96 hours for fathead minnows and Sacramento splittail, and after 48 hours for cladocera. Ground covers significantly reduced runoff volume, but toxicity in runoff samples was not affected. Whereas runoff from esfenvalerate sprayed orchard sections was less toxic to invertebrates than runoff from diazinon sprayed section, esfenvalerate runoff was highly toxic to fish larvae. No fish toxicity was detected in storm runoff collected one month later, but invertebrate toxicity was still significant. Key words: pesticides, storm runoff, toxicity, ground covers |
