Residue dynamics of acephate and methamidophos in urban dooryard citrus foliage, Pompano Beach, Florida--August-September 1978.

Abstract

Residues of acephate and its toxic metabolite methamidophos, attributable to the State-Federal program for eradication of the citrus blackfly (CBF) [Aleurocanthus woglumi Ashby] on citrus foliage, were assessed in urban areas in Pompano Beach, Florida. Eighteen dooryard citrus trees were sampled on two line transects, each ca 1.6 km long, along two city streets. The trees were sampled twice monthly for five months, beginning before chemical treatments were applied, continuing through the acephate treatment period, and ending when residues decreased below the limits of detection. Acephate and methamidophos residues, as high as 302.5 ppm and 15.8 ppm, respectively, were detected on leaves within one day after the first of a series of three treatments. Significant conversion of acephate to methamidophose was observed. Of the 143 samples collected, 114 contained measurable residues of both compounds; methamidophos accounted for an average of 19 percent of the total residues. Both compounds degraded rapidly, however, and residues averaged below 1 ppm approximately four weeks after the third treatment in the series. Average foliar half-lives for acephate and methamidophos were 8.93 days (SD = 2.52) and 8.40 days (SD = 2.55), respectively.