AbstractField trials were conducted near Cabo Rojo and Mayagüez, Puerto Rico, to evaluate the efficacy of crotoxyphos (afpha-methylbenzyl 3-hydroxycrotonate dimethyl phosphate) applied as a whole-body spray to cattle for control of the southern cattle tick, Boophilus microplus (Canestrini). Percent control was determined by comparing numbers of 4.5- to 8.0-mm-sized engorged females present on control and treated animals on days 0, 1, 7, 14, and 21 posttreatment. Crotoxyphos at concentrations of 0.49 to 0.015% a.i. afforded an average control in excess of 92% (92.9 to 99.8%) for all concentrations. Differences in percent control of ticks between concentrations and also between days on which counts were made were determined by analysis of variance to be statistically nonsignificant.
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