The following information is taken from the University of Kentucky guide Ent-11 “Insect Control on Beef Cattle – 2011” and was prepared by Dr. Lee Townsend, Extension Entomologist at the University of Kentucky.
Insecticides have been placed into numbered Insecticide Groups (1 – 28) based on how they work against insects. Continual use of products from a single Group against a pest species (for example the house fly) can lead to reduced control of that species by all products in the Group. In order to minimize fly control failures due to insecticide resistance, do not apply insecticides within the same group repeatedly, even when using different application methods (baits, residual sprays, knockdown sprays, etc.). Rotate among groups during the fly season. For example with house flies, you can alternate between Group 1 and Group 3 for residual sprays and use a bait from Group 4.
Horn fly control can mean an additional 12 to 20 pounds of weight per calf over the summer months and reduced weight loss for nursing cows. Horn fly numbers can be kept below the target level of less than 100 fly per side (200 per head) by a variety of methods. Factors such as cost, convenience, physical layout, and animal movement between pastures should be considered when selecting a control program.
There is no clear information on the number of face flies per head that lead to economic loss. These flies are very annoying but even heavy infestations do not seem to reduce the rate of weight gain. While grazing during the day can be disrupted by these flies, animals will compensate by grazing at night. Face flies can spread pinkeye from animal to animal in the herd but outbreaks of this disease occur even when face fly numbers are low. Control measures should be increased if the incidence of pinkeye has been high.
Dust bags are most effective when used in forced-use situations where cattle have to pass under them daily to get to water or mineral. Hang bags where cattle will have daily access to them. Keep dust bags dry and charged. Do not use Ectiban or Permectrin if pyrethroid resistance is suspected or present. Co-Ral 1% D (coumaphos), Ectiban or Permectrin 0.25%D (permethrin), Methoxychlor 5% Dust, or Rabon 3% D (stirofos), or Python Dust Livestock Insecticide (0.15% z-cypermethrin) formulations are available for use in dust bags.
For back rubbers, use No. 2 diesel oil, No. 2 fuel oil, or label-recommended mineral oil to dilute concentrate. Do not use waste oil or motor oil. Use one gallon of oil solution per 20 ft of back-rubber. Do not use these dilutions as sprays. As with dust bags, these devices are most effective when placed in force-used areas such as mineral stations or entrances to watering sites. Rubbers are more effective against face flies if 18" strips of cloth are tied at four to six inch intervals along the length. Service the devices at least once per week and position in entryways to water or mineral feeders.
Insecticide ear tags can provide good control of horn flies and may provide some reduction in face fly numbers. Horn fly resistance to synthetic pyrethroids is an increasing problem. Install tags after flies first appear in the spring. Use on calves and mature cattle. Do not apply Cutter 1, Terminator, Patriot, or Optimizer tags to calves less than 3 months old. Remove tags in Sept or Oct. If insecticide resistance is suspected, or if pyrethroid ear tags were used the previous year, use an organophosphate insecticide in ear tags, or other control devices.
Feed additives target fly maggots breeding in fresh animal manure. Research results indicate that results can be very variable. All animals must eat a minimal dose of a feed additive regularly. Supplementary control measures must be taken to deal with flies moving in from nearby herds. The insect growth regulator (IGR) methoprene is the active ingredient in Altosid Block, Tub, and Liquid products. The organophosphate Rabon (stirofos) is available as a 7.76% Premix.