By JERRY LITTLE

Ag Notes

Insecticide-impregnated ear tags are a popular means to control pasture flies (especially horn fly). Tags are inserted in late spring or early summer, and the fly control program travels with the animal. However, using tags containing the same class of active ingredient for several consecutive seasons can create populations of the horn fly that are resistant to a whole class of related insecticides. This shows up in the form of a shorter than normal period of fly control, but lab testing would be needed to confirm resistance.

To cloud the issue more, other things could cause reduced fly control. Some examples:

• The 12- to 15-week “fly control clock” starts when tags are inserted. Hanging them too early in the spring can mean protection “runs out” before fly season is over.

• Horn flies moving in from untreated nearby herds can keep pressure high and make control seem less effective.

• Above normal rainfall can keep manure wetter longer and more suitable for horn fly breeding than during hot, dry summers when manure dries quickly and may be less hospitable for horn fly maggots.

Here are some ways to get the most out of your ear tag-based pasture fly control program.

1. Rotate insecticide classes annually. Currently there are three options — organophosphates, pyrethroids, and chlorinated hydrocarbons — but dozens of brand names. Check the label for the name of the active ingredient in the tag to be sure you know what you are using and record the choice each year.

2. This spring, apply tags after horn fly numbers reach about 100 per side per animal. This will keep them from being applied too early. It takes more than 100 flies per side to have an impact on weight gain.

3. Supplement fly control with dust bags, oilers, sprays or pour-ons, if needed.

Staying on a pro-active program will keep resistance problems at bay. For additional information contact the Boyle County Cooperative Extension Service.

Jerry Little is the county extension agent for agriculture/natural resources.