North Dakota State University Extension Service - Burke County |
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Cattle Comments |
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6-14-04 Cattle Comments: Fly Control As the grazing season progresses, fly control will begin. The easiest answer is to do nothing and hope that horn fly populations remain less than 100 per side of the animal. Several research studies, including those conducted in North Dakota, indicate that economic losses in cow and calf productivity occur when the biting horn fly population is greater than 200 flies per animal. Several methods can be used alone in combination to control fly populations. However, since flies can migrate, attempts to control flies on your herd but not on the herd on the adjoining pasture is will provide only partially effectiveness. Ear tags can be installed that contain insecticides. These insecticides can be very helpful in reducing horn fly numbers as long as resistance is not developed. Rotating use of insecticide type from pyrethroid to organophosphate will help reduce insecticide resistant flies. Since peak fly populations occur during July and August, applying insecticides just before and during will provide moist control. Since insecticide ear tags lose their effectiveness over time, the best time to install or reinstall tags would be late June - just prior to rapid fly population increases. Horn flies have a life cycle that starts when the female fly lays eggs on cattle manure. The larvae hatch in one day and then develop in the pupae for 2- 4 weeks before emerging into adults. Several generals can be completed during the summer. Feed additives provide another form of insect control via the manure. Rabon is a larvicide that affects the larva in the manure. IGR – insect growth regulator is an insect hormone that controls larva growth. The beef cow eating a supplement or mineral mix containing Rabon or IGR will provide good control of future fly populations. These products need to be fed early and through out the grazing season for good control. Adequate intake as specified by the manufacturer is required for success. Dusts, oilers and sprays work very well as long as the cattle are treated regularly throughout the season to maintain control. The high labor effort required to provide continual applications and the need to treat all animals lead herd managers to consider alternatives. 'Pour on' parasite products can also control horn fly populations. In general, the longer the product residual, the longer the horn fly control. Internal parasite control has been shown to be beneficial increasing weaning weights and cow body condition in several studies. Pour on parasite control products that control internal and external parasites can also be used to control horn flies. The ivermectin - type products that have residuals that claim up to 28 days or more of adult horn fly control with one application. Multiple applications can be administered for season long control of horn flies, internal parasite and other external parasites. However, if expense is a concern, an alternative would be one application in late June of the long residual ivermectin - type products. This application would be provided just prior to the start of the exponential growth of horn fly populations. Many options exist for horn fly control. Used alone or in combination these options can reduce horn fly populations to less than 100 per side of the animal. Dan Folske |
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