NEWSLETTER ARTICLES

Livestock and Natural Resources

FLY CONTROL ON BEEF CATTLE
by Wayne Jensen

This is a topic I have written about in this newsletter a number of times. I have also spent time over the years looking at methods to help reduce these parasites. Last year a number of advisors participated in a study where we tracked the activity of the major external parasites of cattle throughout California, and that information will soon be published.

When it comes to control, however, especially with horn flies and face flies, pesticides in some form are usually the method of choice. As with other pesticides, in order to use them in California, they must be approved for use with a California registration. For the past few years, Dr. John Mass, Extension Veterinarian, U.C. Davis, and Dr. Nancy Hinkle, Extension Veterinary Entomologist, U.C. Riverside, have reviewed those materials registered for use in California and made this information available. The following is their report:

This year (1997), there are once again major changes in the list of approved eartags and other drugs available for fly control for cattle in California. There are new product names and companies on the list. Below are updated lists for your review prior to the fly season.

Fly control is aimed primarily at horn flies and face flies. Horn flies bite the cattle and suck fluid from them. In the case of heavy horn fly infestations, their activity will cause the cattle to have decreased weight gains and thus affect production. The face flies are particularly bothersome because they irritate the animals’ eyes by using rasp-like mouth parts to cause the cattle to increase tear production. The face flies then feed on the excess tear secretions. Even more damaging is the fact that the face fly transmits the causative agent of pinkeye, Moraxella bovis. This bacterium (M. bovis) causes tremendous damage to the eye. The last few years have been particularly bad for pinkeye with large economic losses. Additionally, the pinkeye bacterium tends to develop resistance to commonly used antibiotics, which frustrates treatment attempts. Therefore, one of the keys in pinkeye prevention is face fly control.

Both face flies and horn flies develop resistance to insecticides over time. It is important, therefore, to alternate the class of drugs you use to fight flies. For eartags, you should switch between organo-phosphates and pyrethroid compounds every year. Additionally, if you use sprays and eartags, we suggest using one class for the spray (pyrethroids for example) and another class for the eartags (organophosphates for example). The classes of drugs in these different delivery systems can be alternated the next year. The use of eartags is quite helpful for face fly control. However, it is recommended that eartag application be delayed until fly populations are relatively high, so that the possibility of flies developing resistance to the insecticide(s) is decreased. Sprays, back rubbers (face rubbers), and dust bags can be helpful in reducing fly populations early in the season before eartag application. Then, as the number of flies increases to higher levels, fresh eartags can be applied to achieve maximum benefit. Be sure to follow the manufacturers’ label directions for eartags, if they call for two eartags, use two; if they recommend eartags in calves, use them in the calves. For face fly and pinkeye control particularly, the calves are the most susceptible and need protection the most. In the fall, be sure and remove all eartags. If the tags are left in the cattle, the flies that overwinter will develop resistance to the drug you used, and it will no longer be effective.

A new class of compounds is available and is referred to as Insect Growth Regulators (IGRs). These compounds kill fly larvae in the immature stages — before they have a chance to hatch into pesky flies. These IGRs are very safe for cattle and for people working with these compounds. Also, there is no chance for cross-resistance with the other insecticides. Methoprene is one of these IGRs and is used in minerals or other supplements. Another IGR is called diflubenzuron and is in a slow release bolus, Vigilante^®. The bolus is given orally, resides in the rumen and releases the drug for 150 days. These IGRs pass through the cow’s digestive system into the feces where both the face fly and horn fly larvae mature. In the cow manure, the IGR acts to prevent the larvae from developing into adult flies. Since both the face fly and horn fly must develop in cow manure, these products could sharply decrease the numbers of flies. The IGRs could be used early in the season to depress fly populations.

Some important considerations are: (1) Plan ahead for insecticide purchases — fly season always comes; (2) consult with your veterinarian regarding the active ingredient in these products and the history of effectiveness in your cattle; (3) always follow the instructions on the label — these products can be potentially toxic to you, your children, and others working with the product or around the chute, and (4) always follow label withdrawal times and keep accurate records of treatment dates, products, and lot numbers.

, Rotator^®, Ear Force Ranger^®, Saber Extra^®, Excalibur^®, and Commando^® are licensed for use in states other than California. These products are not necessarily different or better than the products listed in the table above.

SLOW RELEASE BOLUS WITH INSECT GROWTH REGULATOR

Drug	Brand Names
diflubenzuron	Vigilante

ANIMAL SPRAYS

Drug	Brand Names
dichlorvos	Vapona
permethrin	Ectiban, Permectrin, Atroban, Permethrin, Insectrin
tetrachlorvinphos	Rabon
tetraclorvinphos+dichlorvos	Ravap

POUR-ON APPLICATIONS

Drug	Brand Names
permethrin	DeLice, Expar, Hard Hitter

BACK RUBBERS AND FACE RUBBERS

Drug	Brand Names
permethrin	Ectiban, Insectrin
tetrachlorvinphos+dichlorvos	Ravap

DUST BAGS

Drug	Brand Names
tetrachlorvinphos	Rabon dust

FEED-THROUGH INSECTICIDES

Drug	Brand Names
tetrachlorvinphos	Rabon oral larvicide
methoprene	IGR mineral, Starbar

NOTE: Active ingredients are available under a number of brand names, and the ones listed above are examples only and are not specific endorsements or recommendations. ALWAYS READ AND FOLLOW THE LABEL INSTRUCTIONS.

A word of caution about those materials that act as larvicides. I have no direct experience with the materials mentioned, but in previous years when I was introducing beneficial dung beetles, I did learn larvicides were also effective in killing the larvae of the three beneficial dung beetles we were working with at that time. I would think their population would also be affected by these IGRs, but only from the animals treated with these materials. Since these beetles are well established throughout wide areas of the county, the population of the beneficial dung beetles would continue to persist on ranches choosing to use other fly control methods.

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