Fly Control in concentrated animal feeding operations such as dairies is a challenge, especially as the weather heats up and there is abundant moisture. Flies not only are a pest but they also decrease production efficiency. Flies cause livestock to expend extra energy fending them off instead of resting, feeding and milking. Other issues directly associated with fly pest problems on dairies include increased medication costs, veterinary costs, increased potential for disease spreading, and possible increased public complaints. For example it is estimated that Stable flies (biting, blood-feeding fly) can lower milk production by 15 to 30 percent (Westbroek, 2002) additionally, contagious mastitis is also spread by high fly populations.
Identifying the type of fly or flies that you are dealing with on the dairy along with understanding their lifecycle is key to develop an effective fly management plan. Common flies found on dairies include house flies, stable flies, and blow flies. These flies are commonly classified as “filth flies” as they like to breed in spoiled/spilled feed, bedding, decaying organic matter and manure. They also prefer moist conditions. Which given the increased moisture this spring adds to the challenges for livestock pest management (Campbell, 2005).
Sanitation is critical in controlling filth flies. Areas to concentrate cleaning efforts in fly control management include: cattle pens, drainage areas, manure storage areas, loafing sheds, stalls, feeding aprons, feed mixing areas, or any other place where there is decaying organic matter. These areas should be cleaned and have organic matter moved away and spread on fields if possible every 10 days to break the fly’s reproductive cycle. Manure stored in silo-type storage units may crust on the top, but cracks allow flies to deposit eggs in wet material below the crust. Agitating and/or adding water may be necessary as fly larvae drown in water (Campbell, 2005). The periodic rains we have been receiving have helped drown fly larvae in large lagoons. Insecticides can be used to treat fly-breeding areas. Be sure to read the insecticide label to make sure the product is labeled for use on dairies in the area being treated.
It is important to remember that if you graze your cattle and do not keep them in dry lots or freestall barns they may also be attacked by horn flies and face flies. Horn flies are blood sucking insects that can bite an animal up to 20-40 times per day to feed. This deters grazing and feeding resulting in decreased intake and milk production. On the other hand, face flies primarily feed on animal secretions around the eyes and nose and are the common means of spreading the pinkeye bacteria, Moraxella bovis. It is important also to note that both species also lay their eggs in manure so manure management in pastures by dragging will decrease fly breeding grounds. Fly control for cattle going to pasture is best achieved if the animals are forced to pass under low-hanging dust bags or oilers so their face and back get treated. Once again, it is important to check the label of the products used to make sure they are approved for their use in both lactating and non-lactating dairy animals.
Control of filth flies is best achieved with sanitation and a combination of knockdown and residual sprays (Campbell, 2005). It is important to read the label of knockdown or residual sprays as many are not cleared for use on lactating dairy cows or in the milking parlor. The best time to apply insecticides for fly control of house and stable flies is during the hottest part of the day. At that time the insects retreat to cooler areas such as vegetation around pens, under bunks or shaded areas. Knockdown sprays are most effective when the air temperature is between 65 °F and 90 °F. Residual sprays should only be applied to shaded fly resting areas because ultraviolet light breaks them down when exposed to the sun. Rain may wash some residual sprays off or decrease their effectiveness so they may need to be reapplied.
One area of fly control that is often overlooked on dairies is fly control in calf hutches which may produce enough house and stable flies to be considered an economic problem. These flies act as vectors for viruses and bacteria/agents for diarrhea between calves, not to mention the dangers of maggots during dehorning and around the umbilical cord. Weekly cleaning or moving of hutches to cleaner “sun-dried” areas during the warm summer months will help reduce the breeding ground for these flies.
For further questions about a fly control program on your dairy please contact the SDSU Dairy Extension team, Alvaro Garcia, Extension Dairy Specialist or Tracey Renelt, Extension Dairy Field Specialist.
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