Merck Double Barrel® Vp Insecticide Ear TagsDOUBLE BARREL VP INSECTICIDE EAR TAGS Quickly knock down horn flies and face flies. DOUBLE BARREL VP INSECTICIDE EAR TAGS combine two active ingredients to effectively take out performance robbing pests for up to five months. Dosage and Usage: Use two tags per head (one in each ear) for optimum control. Apply when flies first appear in the spring and replace as necessary. Tags remain effective up to 5 months; remove tags in the fall. Store in a cool