Rain will not remove the active ingredient from the tag. When on the animal, the active ingredient locks onto the oils on the coat. This results in a higher degree of rainfastness. Following rain, fly activity may temporarily increase due to further fly emergence.
Summer Mastitis and New Forest disease
Flies are associated with the transmission of these diseases. Fly control can help reduce the disease incidence. Fly-borne diseases can have incubation periods of variable lengths (weeks rather than days); symptoms which appear in mid to late summer may be due to an infection transmitted by flies earlier in the season, therefore early attention to fly control methods is important. However, the use of any method of fly control does not mean that any other precautions can be omitted (e.g. infusion of heifers and dry cows with longacting antibiotics, separation of stock with New Forest disease etc.).