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   Hooter McCormick

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PACER AWARDS 2007

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SUMMER MANAGEMENT SERIES

• Fly Fight
• Preventing Pinkeye
• The Rebreed

• TRAILS
• RIDING THE GAP

Back rubbers and dust bags can be put in gateways where cattle travel every day, or near water sources. Oral larvacides in mineral mixes or given by bolus kill larvae after eggs are laid in manure. This is effective for 8 to 12 weeks, unless flies come in from untreated herds. Pour-on chemicals and sprays can reduce flies but must be repeated regularly. Insecticide ear tags can be put in at the start of fly season and the animal does the rest, rubbing insectide over shoulders and body as she slings her head at flies.

Insecticide Resistance to Fly Tags
The first fly tags contained pyrethroids, but by mid l980’s flies began to develop resistance to pyrethroids. Organophosphate tags were the next step. Resistance occurs because a small percentage of flies withstand the effect on their nervous system or produce an enzyme that breaks down the chemical before it can kill them. These flies survive, and though they are a minority at first, they are soon the majority, since they live to produce offspring--and their resistance is passed on.

Horn flies’ life cycle is about 11 days, with many generations per season. With suseptible flies killed off, resistant flies soon increase dramatically. This occurs faster in regions with a long fly season. In northern climates it took years before resistant flies were noticed whereas in the South resistance occurred sooner. In mountain regions fly season is longer at lower elevations so resistance problems occurred first in the lower valleys.

Resistance has been sped up by applying insecticide at low levels. Insecticide ear tags work best with two tags per animal, one in each ear--or four tags per cow-calf pair. Some stockman put one per animal, and some use only one tag (in either cow or calf—only 25% of recommended dose of insecticide). But dosage that low can cause fly resistance. One company developed an organophosphate tag approved for one per animal (two are still recommended for optimum control of horn flies). Test results showed these tags perform well at one per animal, but not for as long; fly control with just one tag drops dramatically after 12 to 14 weeks. The protection may run out when needed most.

Most ranchers put two tags in either cow or calf. It’s better to put both in the cow rather than both in the calf. The cow has more body surface; more flies are killed and she does a better job of spreading insecticide onto the calf than the calf can spread it to the cow. Don’t depend on tagging just calves. Studies show that if just the calf is tagged you get only 50% of the fly control you’d have if tagging the cow and not the calf.

Resistance is hastened by leaving tags in all year long. After 5 months, insecticide level drops below what will kill flies, and continues to drop til there is none left. In a late fall, if flies are still active after tags lose effectiveness, low levels lead to fly resistence. It’s wise to remove tags in the fall.
Use of the same type of insecticide for many years will result in fly resistance, no matter how well managed your program. You must rotate between synthetic pyrethroids and organophosphates. In southern regions with long fly seasons, this alternation should be done yearly or even more often. In northern areas, the same class of tag can be used 2 or 3 years before switching--to allow time for resistance to one type to disappear from the main fly population before that type of tag is used again.

If you’ve used organophosphate tags for 2 or 3 years, you can switch back to pyrethroid; second or third-generation pyrethroids may work as well as early ones did. Most veterinarians recommend organophosphate tags for 2 years, then pyrethroids for 1 year, then back to organophosphates. Flies develop resistance more slowly to organophosphates. Because of shorter fly season in the North and Midwest (15-18 generations per season compared to 20-25 or more in the South), Midwest and northern producers often rotate yearly between organophosphates and the cheaper pyrethroid tags, but the newer, more potent third-generation pyrethroids are recommended and are not as cheap as the older type. Rotating among pyrethroids won’t give adequate control; if flies are resistant to one they are resistant to the others. The same goes for organophosphates. You have to switch classes completely when you change to a different type of tag. Many vets don’t recommend the new tags that contain both classes; eventually flies will develop resistance and then you’ll have nothing to switch to.

To know if tags are working, observe the number of horn flies on the backs and shoulders of your cows. If you recently tagged them and still see large numbers of flies, you have a large population of resistant flies.

When to Tag
Don’t tag too early. Cattle can tolerate low fly populations in early spring. Reserve your most effective weapon for when large numbers take a toll on unprotected cattle. Tags should be installed when there are 50 to 100 flies on each animal. Some tags are effective up to 5 months; if you can wait til May or later to put them in, the better your season-long control will be.
The most important time to control flies is during lactation, for most economic advantage—it can make a difference in weaning weights. If you wean in Fall, install tags in early June. Use pour-ons or dust applicators earlier than that if needed. If you wean in mid-summer, fly tag the cows earlier.
Tags are most effective the first 60 days; tagging in July gives excellent control through the peak of the fly season. If you tag in May before cattle go to pasture you can use a different insecticide as a pour-on, dust bag or oiler, starting early August (this may not be feasible if cattle are on summer range). Using a different insecticide late in the fly season will kill any that are becoming resistant to the tags, and will kill any buildup of flies due to waning of the tags’ effectiveness. This reduces the number of resistant flies going into overwintering phase, making fly control easier next year.

Feed-Through Fly Control
Several products are marketed as feed-through larvicides, put into the mineral/salt mix or feed. Since most cattle are on pasture during fly season, more cattlemen use these in a mineral mix rather than feed. When cattle consume the product it goes through the digestive tract and ends up in the manure. Horn flies lay their eggs in fresh cattle manure, and when the eggs hatch, the immature larval stages are hindered by the active ingredients in the feed-through product.

Dr. Jack Lloyd, University of Wyoming, says there are a couple ingredients that can be used in these products. “The one Moormans use in their mineral mix is methoprene, which is an insect growth regulator. It’s not a widely used approach to fly control, but it works if your cattle are isolated and not near other herds. The methoprene mimics a juvenile hormone in the insect, making it stay in the larval stage longer than would be healthy for it,” he says. They can’t live forever in the juvenile stage and eventually die.

Fly resistance has become a problem with ear tags because so many stockmen use them, but Lloyd does not envision this ever becoming a big problem with feed-through products. “Theoretically it could happen because insects are very resourceful and at some point in time they could become resistant; there could be some changes in the insect that would make it less susceptible. But I don’t think there is enough of this product in use right now to put that kind of pressure on the fly population--to create resistance.”

A bigger problem with using a feed-through is that you need to be in an isolated area. Otherwise flies will migrate to your herd from surrounding areas. “When we were doing research using boluses containing an insect growth regulator, which is the same sort of approach but affecting the cuticle of the insect so it can’t go from one stage to the next and dies in the molting process, we still didn’t see significant fly reduction in our trial, even though we knew every animal was treated,” says Lloyd. The reason for that was the fact there were plenty of cattle near enough to provide migrating flies into their test herd.

About 10 percent of flies found on your cattle are coming in from other areas, at any given time. So you really need to have an isolated herd where there are no other flies coming in, for a feed- through product to work very well.

Another problem with reliance on this type of product in a mineral mix or salt block is variability of consumption. Some times of year, and on some pastures or feeds, cattle eat more salt or less. And some individuals will always consume more while others eat very little, or none. With this kind of variability, the effectiveness of the feed-through control is also variable.

Natural Ways to Reduce Horn Flies
In recent years some stockmen have been looking at ways to control flies without resorting to chemicals. One method is use of diatomaceous earth (silica powder from sedimentary rock which contains the remains of ancient one-celled plants deposited at the bottom of old sea beds in what is now part of the western U.S.), mixing it in livestock feed. Much of it passes on through with manure, where it inhibits fly larvae. The theory is that this powder is microscopically sharp—not enough to hurt the animal internally, but enough to possibly scratch the protective coating on fly larvae as they move around in the manure. The drawback to relying upon this method is that it has not been scientifically proven to work very well.

Another way to break the flies’ life cycle is with predator wasps. These tiny nocturnal wasps are harmless to humans and animals and spend their entire lives on or near manure. The females search through manure and lay eggs in the pupae of house flies, stable flies and a number of other flies. The wasp eggs hatch quickly and use dormant fly pupae as food, killing the fly before it can develop.

These wasps are generally present wherever there are flies, but not in large enough numbers to control their population. You can purchase more wasps, however, and if you release them early in the fly season and put out more periodically through summer, you may be able to reduce fly numbers.

In large pasture areas this is not very practical, but around barns, corrals, feedlots, and other confinement areas, it may help. Suppliers of fly parasite wasps recommend spreading them on the manure in corrals, early in the spring before flies are numerous, and putting out more wasps every 30 days. The number of wasps needed depends on the number of animals on the premises. If you use biological fly control, however, you must not use insecticides or they will kill the wasp population along with the flies.

Another natural way to control flies (and more effective for horn flies) is dung beetles. These beetles spend their lives in manure and the adults use the liquid contents for nourishment. They lay their eggs in manure and some types bury the eggs in balls of manure. Bill Clymer, PhD (parasitologist in Amarillo, Texas) says dung beetles are our best allies for controlling parasites that depend on manure for their life cycle.

“In Australia they are used for horn fly control. Studies show that these beetles bury 95 percent of the horn flies and 90 percent of the eggs from internal parasites,” says Clymer. The beetles’ activity—tunneling and burying—disrupts the life cycle; even if the eggs hatch they can’t get back up to ground surface.

“Several years ago I was doing horn fly research in south Texas with ear tags. A flight of dung beetles moved in and we had to do the study over again because my control group (that had no insecticide tags) all went to zero. The dung beetles completely eliminated horn flies in the manure,” says Clymer. A good population of dung beetles can effectively control them. Several types of beetles were imported in the 1970’s and 80’s into North America and Australia. Our native species are good, but not quite as effective as those from Africa, according to Clymer.
Long term control of flies is better achieved with beetles than with sporadic application of toxic chemicals. Fly resistance to chemical weapons (such as insecticide ear tags) becomes a problem when relying upon chemicals alone. Mechanical destruction of the manure pat by beetles is more dependable.

But if you are going to use natural methods of fly control like dung beetles or parasite wasps, you must be careful when using insecticides or you will destroy the wasps or beetles. And some types of dewormers/pesticides (such as ivermectin) will eventually decimate dung beetle populations because they are lethal to the larval stages of the beetles. When selecting a fly control method, it pays to learn all you can about how to make it most effective, and if you opt for natural control you need to make sure you are not inadvertantly defeating your goal by use of certain chemicals or other types of pesticides.


Face Flies

In earlier years it was thought that face flies had sponging mouth parts similar to those of the common house fly, but in 1993 Kansas State University researchers discovered (with use of an electron microscope) that the face fly has very sharp microscopic teeth. Located on the end of the fly’s tongue, these teeth are used to irritate the eye, making it water. This gives the fly access to the mainstay of its diet—the protein-rich eye secretions. Then the pinkeye bacteria more readily gain access to the eye, via the tiny wounds in the cornea caused by the bites of the face fly. The scrapes reduce some of the eye’s protective defenses. Also, if flies scrape an infected eye and then move to another animal, they transmit the bacteria to the next animal.

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