ENVIRONMENTAL MONITORING RESULTS OF SPINOSAD AERIAL APPLICATIONS FOR THE MEXICAN FRUIT FLY ERADICATION IN VALLEY CENTER, SAN DIEGO COUNTY, 2003

The California Department of Food and Agriculture (CDFA) commenced a series of spinosad (GF-120 NF Naturalyte Fruit Fly Bait) applications in 2003 at Valley Center, San Diego County to eradicate an infestation of the Mexican fruit fly. A total of thirteen aerial treatments were conducted from January 10th to May 30th. The treatment was a spinosad-water mixture applied over 23 square miles. Target application rate was 20 oz/acre of GF-120 NF bait or 3.26 microgram per square foot (μg/ft) of spinosad. The Department of Pesticide Regulation (DPR) monitored applications throughout the aerial treatments. DPR measured the amounts of spinosad sprayed from aircraft and deposited on the ground, and analyzed the concentrations of spinosad residue in surface water, rain runoff, air, and fruit samples. Mass deposition of spinosad ranged from none detected to 9.63 μg/ft and the overall average was 1.58 μg/ft, 48.2% of the target application rate. Average spinosad deposition for each application ranged from 0.557 to 2.12 μg/ft with standard deviations from 0.326 to 2.44 μg/ft. Average over time for each sampling site ranged from 0.544 to 3.90 μg/ft with standard deviations from 0.581 to 3.56 μg/ft. A two-factor analysis of variance indicated that significant differences existed among applications (P = 0.005) and among monitoring sites (P = 0.007). Correlation analysis indicated that the average spinosad deposition for each application was not significantly correlated to reported application rate, tank mix concentration, air temperature, relative humidity, wind speed, or site elevation. Sunrise time at Valley Center was significantly correlated to deposition mean (r = 0.765). Sunlight affecting spinosad stability was indicated by the results that deposition means of the five samples collected in direct sunlight during three applications were significantly lower than the average of the remaining samples from these three applications (P = 0.00171). However, detailed comparisons of mass deposition to sampling time for each sample during each application showed no perceptible relationships. This may be explained by the trees and hilly terrain in Valley Center, and that samples collected after sunrise were not always in direct sunlight. Of the samples collected in designated non-aerial treatment buffer zones around main water bodies, 59.3% of the samples had positive detections of spinosad ranging from trace amounts to 1.59 μg/ft. The average of the buffer zone samples was 0.162 μg/ft, 10.3% of the average for the aerial treatment area. Spinosad residues were not detected in the surface water, rain runoff, and ambient air samples. However, these non-detections were ambiguous because storage stability studies for water samples and trapping efficiency studies for air samples were not satisfactory. Fruit sample results ranged from none detected to 0.162 parts per billion (ppb), with an average of 0.025 ppb spinosad residue. There was no significant difference (P = 0.208) between samples collected from the upper portion versus the lower portion of the canopy. The pesticide GF-120 NF concentrate samples contained 193, 208, and 223 parts per million (ppm) spinosad for each of three DPR sampled applications. The label states this product contains 200 ppm (0.02%) spinosad by weight as the active ingredient and no other active ingredients. The spinosad concentrations in tank mix samples ranged from 76.3 to 202 ppm, 95.4% to 253% of the target application rate, 80 ppm. No detectable organophosphate, carbamate, or chlorinated hydrocarbon pesticide residues were found in any samples of the spray materials except for two tank-mix samples. DPR detected 5 ppm of malathion in the tank mixture samples during the third application and 290 ppm of malathion during the fourth application. A subsequent investigation by DPR and CDFA indicated that a manifold used in the mix/load system was the likely source of contamination (Appendix I). Though the 290 ppm malathion was relatively high compared to the spinosad concentration, it was only one to two percent of the normal malathion application rate. Samples of deposition, water, air, and vegetables collected from the treatment area during and following the fourth application showed no detectable malathion residues.