Buzz Off!

Published on Wed, 05/02/2018 - 1:31pm

Buzz Off!

 By Michael Cox for American Cattlemen Magazine

 Despite some challenging cold weather throughout the States this Spring, the summer heat has inevitably arrived, and with it, the nuisance issue of controlling flies on cattle. Summer fly control is a crucial component of a profitable rancher’s management plan, as fly irritation to cattle can greatly reduce daily live-weight gain and lead to animal health issues such as pinkeye. Flies disrupt grazing, particularly in growing calves, leading to lighter weights come weaning time. The horn fly is typically the worst summer offender, with face flies and stable flies also contributing to the pest pressure. Horn flies have a rapid lifecycle of 10-11 days allowing an explosion in fly populations to occur in a matter of a few weeks. The threshold level for cost-effective fly control is 100 flies per calf and thankfully, there are many options available for effective fly control.

The majority of fly control options are chemical based, although there are a small number of natural preventative measures that can be taken.
Insect Growth Regulators (IGR) are a low-labor fly control option. IGRs can be fed to cattle through feed supplement or minerals. The compounds have no negative effects on animal performance, as they specifically target the larvae development of the flies. Care must be taken to ensure that sufficient intakes are being regularly achieved by the cattle, particularly if the IGR is delivered through free-access minerals. Most IGR products recommend that the feeding program begins approximately one month prior to fly emergence.
Dust bags and back rubbers/curtains are another labor friendly option that rely on physical contact with the animal to deposit insecticide onto the face and back area of the cattle. The applicators must be set up in a high-traffic area where cattle will regularly pass under them to access water or feed. Animals should be grouped according to size/height to allow equal application to every animal. Apart from protecting the applicators from rain and replenishing the insecticide, there is almost no maintenance or workload involved in this control method.
Summer worm-control treatments can also be a useful method of ‘doubling-up’ as a fly-control treatment. Ivermectin pour-on based products used primarily for roundworms, lungworms etc. will also offer a short time period of horn fly and lice protection. The fly control benefit of pour-on products should be viewed as an added bonus to worm control, as pour-ons are usually insufficient for use as a full fly control option on its own.
Direct insecticide spray offers cost-effective prevention and can be best used to rapidly reduce fly-load on badly affected cattle. Some fly sprays can be diluted with oil or diesel to help the insecticide stick to the hair for longer. Resistance issues can build up over the season if the same class of insecticide spray is used repeatedly.
Insecticide impregnated ear tags offered excellent control when first introduced over 25 years ago, however resistance issues were quick to develop after several years of continuous use. Fly tags can still be useful nowadays, but ranchers should take some steps to reduce resistance. The insecticide class should be rotated every year, cattle should not be tagged too early in the season (200 flies per animal is the recommended minimum threshold level), all cattle in the group should be tagged at the same time, other control methods should be used later in the season when tag effectiveness declines and fly tags should be removed in the autumn.
For ranchers with small herds, or for cattle located on land with poor handling facilities, a Vet Gun can be a useful tool for summer fly control. The Vet Gun is a device similar to a paint-ball gun, which allows the rancher to shoot insecticide capsules onto the animal while in the pasture. The capsules explode on impact with the animal and deposit the insecticide onto the animal’s hide.

Non-chemical control
Non-chemical fly control options include natural predators, vacuums and pasture rotations.
Parasitic wasps are a non-stinging predator wasp that feed on flies. Parasitic wasps can work well in small areas, such as cattle confined in feedlots. The wasps tend to travel only short distances and are less effective in larger, open pasture situations.
The Cow-Vac is a relatively new technology that essentially vacuums flies off cattle. The Vacuum is a stationary device and requires animals to pass underneath, much like back-rubbers and dust bags. The Cow-Vac has proven particularly useful in many organic dairies although its use in beef herds is becoming more common. The vaccum’s collection of flies is an excellent method of reducing fly populations and if carried out regularly can help to minimize the fly burden right throughout the season.  
Grazing pastures in rotation every 18 to 30 days will allow cattle to ‘escape’ the fly larvae before they hatch out, and help ease the fly burden. As most fly species complete their life cycle in 10 to 15 days, the pastures will have less fly population if herds can be moved regularly to fresh pasture and the rotation length can be extended to more than 15 days.
Like most things in ranching there is no one-size-fits-all solution to fly control. Many of the options discussed above will work best if utilized in combination. Resistance to any form of chemical control can build up over the season so it is advised to not start treatments too early in the season, and to ‘top-up’ treatments only as required. Many products will be effective for 4 to 6 weeks, and possibly longer depending on weather conditions and fly populations.