Permethrin applied as a spray to cattle at 0.025% or 0.05% effectively controlledBoophilus microplus(Canestrini) by the third day post‐treatment, but only provided < 60% control within 1 day post‐treatment with both concentrations. Percentage control did not drop below 90% until day 28 for 0.025% and day 31 for 0.05% permethrin; percentage control did not fall below 92% for 0.025% fenvalerate until after day 24–25; and at 0.05%, fenvalerate provided 95% control until day 28. A multiple treatment (spray applied every 2 weeks) with permethrin (0.05%) provided greater than 96% control ofB. microplusafter the initial treatment and 100% control by day 56. We concluded that although both chemicals have potential in an eradication program, they are not satisfactory for use at a quarantine line because both acaricides provided less than 100% control within 1 day post‐treatment.