Ask the Vet

Fly Control Challenges

Backrubs and dust bags are an old, but effective, way to boost fly control. (PF photo by Becky Mills)


We use a feed-through fly control in our mineral, but I'm afraid we didn't start it early enough this season. The flies seem to have gotten ahead of us and stayed ahead of us. What is the best strategy for fly control you've seen, paired with a feed-through?


Every year is different, and weather patterns have a huge impact on fly control. I think we must have a realistic goal of control and not think of this as total elimination of flies.

Horn fly control is by far the most important because they can carry disease and can drain enough blood through biting to cause a severe economic drain on a cattle production operation. Face flies do not bite but feed on secretions around the eyes. They are a significant factor in pinkeye transmission.

Even if you had started the feed-through earlier, in most cases you would have needed other control methods over the course of a season. Effective fly control utilizes an integrated pest management (IPM) program. Selection of the right class and application method are where professional advice is most valuable. Talk to your herd veterinarian, local extension agent or other experts to help develop a customized program specific to your operation.

I believe some type of feed-through (larvacide or insect growth regulator) should be part of every IPM program. There is little documented resistance to these products. Feed-throughs should ideally be started before flies emerge in the spring, and their use should continue until about a month after the first killing frost.

Insecticides can be incorporated into your IPM by various methods of delivery. Ear tags have been a mainstay of fly control for many years, but since they lose effectiveness over time it's best not to apply them in the early spring. Rather, wait until horn fly numbers reach economic thresholds of about 50 flies per cow. Be sure to remove tags in the fall. Always follow label directions as to the number of tags to apply and whether calves also need to be tagged.

Pour-ons can also be effective in reducing fly numbers, but they require working cattle through a chute. Pour-on dewormers provide some fly control and can be part of an IPM program, but they should never be used strictly for fly control. Many experts feel repeated, indiscriminate use of generic ivermectin pour-on products, for example, have selected for resistance in intestinal parasites to this important class of dewormers.

Other options to manage flies include sprays, which may be less time consuming and less stressful than a pour-on because cattle only need to be penned to be treated. Some producers like the VetGun--I call it an insecticide paintball gun that delivers a dose of insecticide. Backrubs and dust bags are old standbys that can be quite effective, but cattle must be forced to walk under them to get to water or minerals, and they must be kept charged.

Lastly, parasitic wasps and fly traps are non-insecticidal concepts that may help in some operations. And don't forget, pasture rotation and manure management around heavy use areas can go a long way in reducing fly populations by limiting breeding areas for the pests.