Abstract
Spraying yearlings with 2% Co-Ral in July was 100% effective for systemic control of cattle grubs (Hypoderma spp.). Spraying spring calves with 1% Co-Ral in August was equally effective, and gave better control (P < 0.01) than spraying with 1 or 2% Co-Ral in June or 0.5% Co-Ral in July. Co-Ral sprays were not suitable for horn fly (Haematobia irritans L.) control.Two per cent Sevin sprayed on calves in June or July did not control cattle grubs, and only partially controlled horn flies.Compared with the control group, the average daily gain was higher (P < 0.05) to weaning but lower (P < 0.05) in the feedlot in calves sprayed with 2% Sevin in June. Similarly, it was higher (P < 0.05) from birth to the end of the feedlot period in calves sprayed with 2% Co-Ral in June, but lower (P < 0.05) in calves sprayed with 0.5% Co-Ral in July.Mild toxicosis occurred in five calves sprayed with 2% Co-Ral in June, and subclinical toxicosis in calves sprayed with 1% Co-Ral in August.

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