Horn flies (Haematobia irritans irritans) and face flies (Musca autumnalis) are common insects in grazing animals in most of the world. The current study was designed to evaluate the efficacy of 40 % diazinon impregnated eartags (Patriot T) in reducing horn fly and face fly pressure in cow calf pairs in Missouri, USA. Seventy cow calf pairs were randomly assigned to one of two treatment groups i.e. Patriot Group and Placebo Group. On study day 0, cows in Patriot treatment group were tagged with two insecticide impregnated ear tags (Patriot Ear Tags), while the calves were administered one tag. Placebo group animals were administered placebo ear tags in a similar manner as Patriot treatment groups. Fly counts were performed on ten randomly identified cows within each group throughout the study. Beginning on Day -10, fly counts were performed three times (day -7, -3 and 0) to ensure that fly pressure was sufficient prior to Day 0. Post-treatment fly counts were performed weekly on the same 10 cows within each group. The mean horn fly counts per animal in Patriot group were below economic threshold during first 13 week of study period and were slightly above, 215.5 in week 14 and 209.6 in week 15. The highest percent face fly efficacy was observed in study week 5 which was 72.93. The results indicate that 40 % diazinon impregnated (Patriot Ear Tags) were highly effective in mitigating horn fly and face fly pressure for up to 15 weeks.
