Certain states do not recommend the use of oral larvicides or insecticides given through the feed such as tetrachlorvinphos (Rabon), methoprene (Altosid, Moorman's IGR) and phenothiazine. These feed additives often are not the answer to fly control unless used very extensively. All feces must be treated within an area in order to effectively reduce the fly population on the livestock. The area must usually be many miles across because flies do move very readily from herd to herd over an area of several miles within a day or two. This treatment is usually more effective against the horn fly than for the face fly. We have had little success in controlling the face fly by this method. Feed additives do not control house fly and stable fly larvae that develop in sites other than fresh manure.
Oral larvicides, when fed, prevent the development of flies in the manure. They are not effective against existing adult flies. These oral larvicides should be used in conjunction with good manure sanitation. Supplemental fly control is needed where flies breed in manure from untreated animals such as indoor penned young stock or other organic sources.
Rabon 7.76 percent oral larvicide is fed at the rate of 70 mg/100 lbs. body weight (dairy cattle and beef cattle per day) as a premix, loose mineral or block from May through September. Animals must consume the recommended dosage for the feed additive to be effective. This method provides reduction of fly larval development only in manure from treated animals. Follow label directions and precautions.