South Dakota Grassland Coalition

by Garnet Perman

July 2020


The plague of summer! Fly control is part of a comprehensive management plan for cattle. Chemical control has been the method of choice since DDT became available about 80 years ago but resistance to chemicals is an increasing problem. According to Dr. Mike Hildreth of SDSU, no new classes of insecticides are being developed and the permethrins, the active ingredient in most products are less and less effective. Many producers use a pour on that is actually an endocide designed to kill worms. It is effective for flies although it isn’t labeled for that use. Hildreth said, “the danger in using it for fly control is that eventually worms will become resistant and that could present a bigger liability than flies.” Treated ear tags are easy to use, but again, resistance in flies and lice is an issue. Management and mechanical means of fly control may soon be the only means of controlling flies left.

Rotational grazing is one management tool

Moving cattle not only stimulates forage production, but it moves the cattle away from hatching flies. Mechanical options include backrubbers, dust bags, oils, and traps of various kinds. One company has even developed a vacuum system. Traps are used in other parts of the world and work particularly well in dairies where cows get used to walking through them on the way to the milking parlor.

One benefit of foregoing chemical is natural bio controls show up. Dung beetles return to pastures once chemical is discontinued. Their activity limits fly populations and improves soil fertility. High intensity, short duration grazing helps attract dung beetles. Charlie Totton, Chamber-lain, didn’t use a lot of fly control chemical but quit completely five years ago. He thinks the dung beetles were there but in a year or two the population had noticeably increased. He has many tunnelers and found rollers last year. He has also noticed an increase in the number of cowbirds. Several hundred cow birds eat insects flushed up by the herd. White cattle egrets also eat flies.

Linda Simmons in NE South Dakota

Tried several insecticides over the years. Topical products only worked about 50% of the time. A severe horn fly infestation after using a feed-through product, sent her searching for other methods of fly control. She found a walk through trap that was first invented about 90 years ago. The University of Missouri improved on that invention and showed that it could be effective against horn flies. Inexpensive, easy to use chemicals came into wide use about the same time, so the more labor intensive mechanical trap never took off. Simmons applied for and received a Sustainable Agriculture Research and Education (SARE) grant to build it and count flies.

The trap is not 100% effective, but keeps flies down to the 200 flies per cow threshold recommended by the Extension Service. She uses it about four times per grazing season, but it could be used more often if needed. The downside is it needs to be set up and cattle need a bit of training to use it. She mounted it on the mouth of a corral and locked the cows in. They figured out how to get through it on their own. One idea would be to place it at the entrance to a water tank, so the cattle would be forced to go through it at least once a day.

The following links tell more about fly traps: contains information about Simmons’ project. The following link contains more information and pictures of various fly traps:

Source: SDGC Newsletter

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