It’s the time of year when flies and ticks start becoming a problem for cattle, and they can be more than just a nuisance.

“These external parasites not only cause irritation and stress but also reduce production efficiency and serve as vectors for certain cattle diseases,” said Craig Payne, University of Missouri director of veterinary extension. “It’s important to use control practices through an integrated approach.”

Among the flies that affect cattle, horn flies and face flies can be the most troublesome. Horn flies are small, blood-feeding insects that remain on the animal nearly all the time. They feed frequently, sometimes up to 40 times per day, and tend to concentrate along the back line unless they are forced to move to the underbelly due to heat or moisture. Their feeding causes significant stress and economic loss. Face flies spend limited time on cattle, feeding on secretions from the eyes and nose. This causes eye irritation, and the flies contribute to the spread of pinkeye-causing pathogens such as Moraxella bovis.

Beyond their role as blood feeders, ticks carry pathogens, Payne said. One such pathogen, Anaplasma marginale, causes anaplasmosis, which is widespread in Missouri and other parts of the country, causing anemia and potentially death in mature cattle. The recent appearance of the Asian longhorned tick in Missouri introduces additional risk, as this species has been associated with the transmission of Theileria orientalis ikeda, a protozoal organism that causes symptoms similar to anaplasmosis. Heavy infestations of this tick can lead to stress, excessive blood loss and reduced performance.

Timely intervention is critical for effective fly control, he said. “The rule of thumb is that control measures should be implemented once the horn fly count reaches around 200 flies per animal. A practical reference is that 100 horn flies will cover an area about the size of the palm of your hand.”

For chemical control, insecticide ear tags remain a common tool. These tags gradually release an insecticide — it could be a pyrethroid, organophosphate, abamectin, tolfenpyrad or, in some cases, a combination of these compounds — that disperses across the head and back, providing protection. Tags can be effective for several months. To maximize efficacy and minimize resistance development, adult cattle should be tagged with two matching tags, and the tags should be removed at the end of their useful life.

Other control methods include pour-on products or applying approved insecticides with a tank sprayer. These may serve as a primary control method or can be applied later in the season as fly tag effectiveness declines. Their duration of protection is generally shorter, from one to three weeks, and is often reduced by rain or water exposure. Cattle dewormers that also target external parasites may be effective, but repeated use should be limited due to the potential for developing internal parasite resistance.

Feed-through products, such as insect growth regulators and oral larvicides, disrupt the development of fly larvae in manure. These products must be consumed consistently for full effectiveness, and feeding should begin about 30 days before peak fly activity. Though not as widely used, back rubbers and dust bags remain effective in operations where cattle reliably use them and the devices are properly maintained.

Some ear tags are also labeled to control certain tick species, but additional control with a pour-on approved for tick control may be warranted, Payne said. Regardless, controlling tick habitat can be just as important. Practices such as mowing, brush control, fence line clearing or controlled burns can significantly reduce tick populations by limiting the environments in which they thrive.

To address resistance in fly populations, producers should rotate among classes of insecticides and avoid overusing a single product. Horn flies, due to their rapid generational turnover and the fact that they spend most of their life on the animal — and therefore have more time in contact with the insecticide — can develop resistance rapidly, sometimes within a year. The frequency with which compounds are rotated depends on the operation. Some fly tag manufacturers provide a rotation schedule for their product line, but local veterinarians can also provide input based on their experience.

“Incorporating nonchemical methods into a fly control program may also be beneficial,” said Payne. Biological control using parasitic wasps has shown some success in reducing fly populations by targeting larvae. Management strategies such as improving manure handling and using walk-through traps can also reduce fly pressure.