More resistance, more flies, less money

Jul 22, 2011
by DTN

Reduced weaning weights for calves, lower weight gains on yearlings, summer mastitis and pinkeye— they’re all key management points that can mean the difference between a year that ends in the black and one that bleeds red. And at the center of that balance sheet is the lowly fly.

One of the worst is the horn fly. For a pest with a relatively short life cycle, the horn fly can do some major damage. Current estimates are the pest sucks more than $800 million out of cattle producers’ pockets every year. The pests stress cattle, taking between 24 and 38 blood meals per day, per fly, off of the affected animal. Some data shows every 100 flies per cow cuts calf weaning weights by 3-16 percent.

It seems to be getting tougher and tougher to control horn fly populations as they continue to show increased resistance from one year to the next. It’s important to switch the class of insecticide used every one to two years, and to avoid using products until economic infestation levels are reached—about 200 horn flies per animal. There are some relatively new options for control these days providing producers tools to help rotate chemicals while managing pests.

Lee Townsend, Extension entomologist at the University of Kentucky, says one option is the combination tag that contains both a pyrethroid and an organophosphate. “Insecticides with new modes of action are also showing up in tags,” he says. “Examples include abamectin (XP 820) and endosulfan (Avenger). And a spinosad insecticide (Elector) is available as a pour-on for cattle for pasture fly and louse control.”

Grazing methods are key when establishing a fly control program. If intensive grazing and pasture rotation are the norm, it’s easier for fly control to go with the animal in the form of ear tags. If there is a set place where water or minerals are always available, self-applicators can more easily be used. But beyond convenience, Townsend says that resistance has to be a factor in how producers manage fly control.

“There are a lot of product names out there and, often, producers still aren’t sure if they are just changing products or changing classes of chemicals,” he says. “It’s important to break down products, particularly ear tags, by categories the insecticide represents so you know you’re switching to a completely different mode of action.”

This is especially critical with horn flies, which stay on animals 95 percent of the time, just leaving to lay eggs in fresh manure. Their constant exposure to the insecticide in an ear tag, for example, makes it important to remove the tags in a timely manner and to alternate chemistries. Face flies, which only tend to be on the body about 5 percent of the time, can be harder to kill with ear tags.

In the end, it’s all about controlling pests at a reasonable cost and seeing benefits in productivity. “There’s research that shows a 15- to 20-pound difference in weight over the summer for protected versus unprotected yearlings when we’re talking about horn flies,” says Townsend. “It’s almost the only cattle pest where we have that good of an estimate of economic impact.

So look at those pounds and look at your control costs and see if you’re making headway.” — DTN