Producers can reduce fly issues through feed management

Flies are an almost constant nuisance in the agriculture industry.

Horn flies cause an estimated $730 million production loss in cattle annually, facilitate weight loss and can reduce milk production by 4-12 percent. Face flies can contribute to pinkeye and other eye issues, and those are just two species of flies. Wherever a producer falls on the spectrum, a pest control program of some kind is essential and feed through fly control can be an efficient option.

Feed through fly control works in one of two ways – either as insect growth regulators (IGR) or as larvicides.

“Insect Growth Regulators have a mode of action that essentially breaks the growth cycle of fly larvae, preventing them from growing any more. S-methoprene is the most common chemical agent used as an insect growth regulator,” Andy McCorkill, livestock field specialist with the University of Missouri Extension, explained. “The biggest drawback to IGR is that the chemical action is species specific, meaning that it controls only one species of fly. S-methoprene, for example, is labeled for control of horn flies, yet does nothing to aid in the control of face flies or stable flies. Larvicides act slightly differently; they lead to some sort of structural issue within the fly larvae that leads to premature death, subsequently keeping them from reproducing. Many of the common larvicides are organophosphates, similar to the ones used for topical spray or ear tag applications.”

Feed through fly control must be used properly for it to be effective, and timing is critical. If a producer waits until flies are already amassed on the herd, they have waited too long. McCorkill explained that most feed through products are recommended to be fed a month before fly season really kicks in (right about now for the Ozarks) and approximately a month after fly season has ended. It is also important to make sure that animals are eating enough of the product.

“Resistance typically is caused by exposure to less than lethal dosages over time and there have been reports of resistance to feed through organophosphates, just the same as with spray or tag application, so some rotation of active ingredients from time to time could be advisable,” he said.

While properly managed feed through fly control can be a wonderful option for producers, the best pest control plan is typically an integrated system – feed through products are just one spoke on the wheel.

Rotational grazing (which can interrupt the life cycle of flies and other pests/parasites) and manure management can also help reduce the fly count.

“The work of feed through products is really done in the manure pile,” McCorill said. “One strategy to further combat flies in combination with feed through products is to run a drag or harrow over the pastures a few days after the first feeding date of the fly control product to break up old manure without any active ingredient in it to help reduce fly propagation.”

Even if a producer is on point with their fly control, the next-door neighbors may be contributing to the problem.

“Flies don’t recognize boundary fences, just host animals. If your herd is up against a neighbor’s herd that doesn’t have a fly management plan in place, then the best management in the world can’t keep the flies away,” McCorkill said. “Fortunately, horn flies don’t travel very far from their host or manure, so a relatively short separation distance is needed for them.”

If possible, producers can utilize a rotational grazing system that breaks their pasture into smaller paddocks, so their herd is not constantly up against the neighbor’s herd.


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