by Katie Navarra
Without fail, flies arrive with summer heat and increased grazing time. Controlling flies is a common management issue among farmers, especially organic farmers who have fewer options for control. In a webinar hosted by eExtension and eOrganic, Roger Moon, Ph.D. and Brad Heins, Ph.D. at the University of Minnesota, discuss two control options that were researched at the university through a project funded by the USDA Organic Research and Extension Initiative.
Before a method of control can be established, you have to know your enemies. Flies originate from different places and cause specific problems. When asked to name flies, most people first list mosquitoes, horse flies, black flies and biting gnats.
“These flies all come from wetlands, swamps or streams and you may or may not be able to manage them,” he added.
“Filth” flies on the other hand, are flies that come from filthy habitats. Farmers do have options for limiting or controlling these species. The “filth” fly category includes horn, face, stable and house flies.
Stable and house flies breed in accumulated debris such as feed stuff, manure piles, etc., whereas horn and face flies only develop in cow dung, patties, or plops.
“Both horn and face flies don’t develop anywhere other than cow dung,” Moon said.
Horn and face flies are most bothersome in dairy operations. “Face flies come to the face to feed on tears, mucous and liquids. They take a sip and leave,” Moon explained, “horn flies actually live on the cow’s back.”
Horn flies feed on the cow’s blood. These flies cluster on a cow’s back and pierce the skin to draw blood. Each horn fly feeds up to 12 times each day. Studies have found that horn flies can reduce milk production in dairy cattle and slow growth in beef by nearly five percent per day. Traditional dairies have more options for control available than organic operations, but both may benefit from flytraps.
Cattle huddling together in the pasture signal an infestation of horn flies. Conversely, cattle spread out and bedded down in the field are more comfortable and not pestered by horn flies.
Moon urges dairy farmers to pay less attention to face flies. “There’s not much that can be done to control them. While they may carry bacteria and/or spread pink eye, face flies will not affect yield,” he said.
Pour-on sprays or repellents have traditionally been used, but offer temporary relief at best. Sticky traps are also ineffective. Since horn flies live on the cow’s back there is no opportunity for these flies to adhere to a sticky trap.
In the 1930’s entomologist, Willis Bruce who was working for the USDA developed the first walk-through trap designed to catch horn flies. Bruce tested several designs, the result commonly known today as the “Bruce” fly trap. Intended to be installed in an area that cows are required to pass through (such as an entry or exit to water or a milking parlor), the Bruce trap includes strips of canvas or old carpet. As the cows pass through the system, the strips remove most horn flies from the cow’s back and legs.
Over time, researchers noticed that the flies would leave the cow’s back as they entered the trap and then land again when the cow came out the other side.
Since then, the basic design has been upgraded to include a vacuum to suck flies off the cow’s back and collect the flies as the cow passes through.
During the summers of 2013 and 2014, Moon, Heins and their colleagues compared the efficiency of the “Bruce” trap versus a 220-volt system manufactured by Spalding Labs called the Cow Vac. Both set-ups were installed on University of Minnesota’s research farm and fly populations were measured.
“We found the “Bruce” trap removed approximately four and a half percent of the horn flies from a cow’s back each time the cow passed through the trap,” Moon explained, “the Cow Vac removed nearly 21 percent of the flies per passage.”
The next step of the research project was to install a Cow Vac at eight different farms throughout Minnesota. The unit was installed on four farms for eight weeks and then moved to four different farms for another eight weeks. Each farm was an organic dairy and sizes ranged from 30 to 350 cows.
While the Cow Vacs were present on each farm there was an average of 44 percent less horn flies.
When the Cow Vac was removed, fly populations increased. The on-farm study found significant reduction in horn fly populations, but the findings did not show an increase or decrease in milk production. “We were hoping to see a benefit in production and we just didn’t observe one,” Heins said.
Despite the lack of evidence of increased milk production from this particular study, reducing horn fly populations is important to managing a healthy herd. Cow comfort is ranked among the most important factors to milk production. Reducing the number of biting flies that live on the cow’s back increases the overall comfort, that when taken in combination with other factors can increase milk production.