Field Tests with Low-Level Feeding of Ronnel for Control of Cattle Grubs and Horn Flies

Abstract

Four groups of Hereford cattle were offered ronnel in a mineral supplement in feed at the recommended level of 7.8 mg./kg./day for 14 days and/or in mineral blocks in pastures. The effects on populations of horn flies ( Haematobia irritans (L.)) and numbers of common cattle grubs ( Hypoderma lineatum (de Villers)) appearing in the animals’ backs were recorded. Group 1 was offered mineral supplement plus mineral blocks, group 2 mineral supplement only, and groups 3 and 4 mineral blocks only. When the mineral supplement containing ronnel was offered, populations of horn flies were reduced throughout the feeding period and for about 1 week thereafter. Consumption of ronnel in mineral block form varied considerably from group to group and from week to week within a group. A level of 3.5 mg/kg/day of ronnel was inadequate to prevent a buildup in the number of horn flies, but some apparent control was obtained with levels as low as 4 mg./kg./day when maintained for periods longer than 1 week. With group 2 only 40% cattle grub control was obtained; with groups 1, 3, and 4, 78-98% control was obtained.