– Rory Lewandowski, OSU Extension Educator, Wayne County
Fly control in cattle is about reducing fly populations, not elimination. The goal is to limit the negative economic impact that flies can cause. There are three main fly species that can economically impact pastured cattle and those are the horn fly, the face fly and the stable fly. Horn flies are responsible for significant economic losses. According to Dave Boxler of the University of Nebraska, economic losses associated with the horn fly are estimated at more than 800 million per year in the U.S. Those losses are due to decreased grazing efficiency, blood loss, reduced weight gains, and declines in milk production. University of Nebraska studies have shown calf weaning weights to be 10 to 20 pounds heavier when horn flies were controlled on the mother cows. Horn flies are small, about half the size of a housefly and they are blood feeders. Each fly will bite the animal and feed on blood 20 to 30 times per day. The economic injury or threshold level of horn flies is 200 flies per animal.
Horn flies spend most of their time on the animal. The female fly will leave the animal for a short period of time to deposit eggs in fresh manure and then will return to resume feeding. The most common and often the most convenient method of horn fly control is insecticide impregnated ear tags. The disadvantage of ear tag control is that there are horn fly populations resistant to the pyrethroid insecticides commonly used in the tags. In order to minimize and slow down resistance problems ear tags should not be put in until horn flies reach that economic threshold level of 200 flies/animal. Those horn fly ear tags should be cut out of the animal’s ear in the fall of the year when fly levels decrease. Other control measures include backrubbers and dust bags, especially if they can be located in areas where cattle can have daily and consistent access to them. There are insecticide sprays and pour-ons that can provide between 7 to 21 days of control, but to be effective they must be applied on a regular basis throughout the fly season. There are also oral larvacides that prevent fly larvae from developing into adults. Although effective, the challenge is getting consistent, daily consumption. These products can work well for cattle in confinement situations or that are supplemented regularly on pasture, but are more difficult to use in rotational grazing systems.
In contrast to the horn fly, the face fly is a non-biting fly that spends significant time off the animal. This fly feeds on secretions, nectar and manure liquids. Face flies cluster around the animal’s eyes, mouth and muzzle. Feeding around the eyes can cause tissue damage which opens a pathway for pathogens. The female face fly can vector the Moraxella bovis bacteria which is a primary pathogen for contagious pinkeye. Control of face flies can be difficult because of all the time that the fly actually spends away from the animal. As with horn flies, insecticide impregnated ear tags are a common form of control. Dust bags and oilers can provide effective control if, once again, animals can have consistent daily access to use of these options.
The stable fly is a biting fly that will spend considerable time apart from the animal. This is a pest that will travel up to several miles to bite. These flies and their painful, biting attacks are associated with lowered milk production, reduced feed efficiency and lowered weight gains. Agricultural Research Service entomologist David Taylor says that a model developed to look at the economic impact of stable flies on dairy cattle, cow/calf, pastured and range stocker animals and feedlot cattle showed that stable flies cost the U.S. cattle industry more than 2.4 billion dollars each year.
Stable flies are generally associated with sites where waste hay/feed, manure, and urine accumulate because this is the ideal site for larval development. Control is dependent upon sanitation, cleaning up those breeding and larval development sites. Entomologists with the Agricultural Research Service (ARS) have found that insect growth regulators can be effective at reducing stable fly populations. Those entomologists used a commercial product called cyromazine to control immature stable flies by preventing those immature flies from developing into adults. According to information released by the ARS, in one study, the application of granular cyromazine sprinkled on a hay feeding site reduced the number of emerging adult stable flies by 97 percent. Other ARS researchers are looking at the use of repellents to keep stable flies away from animals. Catnip oil has been found to be effective. On the horizon, other ARS scientists are experimenting with a biological control agent, a salivary gland virus that has shown some promise in providing stable fly control in initial trials.
Summer weather is associated with increasing fly populations that can negatively impact cattle performance. Take some time to develop a fly management plan.