NDSU Extension - Ramsey County


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June 30, 2014 Agriculture Column


Rain, wind, rain, wind and more of each and not much heat to boot.  Our crops need a little sun and warmer temps to get them motivated to grow and reach maturity.  Our weathermen that predicted the weather this winter sure have missed this weather.  We held our first ever outdoor 4-H Achievement day livestock show outdoors, at the Peterson Arena and was a success.  We had a couple of misshaps but all in all the day proceeded very smoothly.  We will have to make a few minor adjustments but was a very good location for such an event.  It is really fun to watch and visit with livestock families and their willingness to pitch in and help where ever needed.  We had a couple of beef calves that needed some extra attention and there was always someone wanting to give that extra hand. Congratulations to all the families involved with the outdoor show.  I might add that we had three former livestock 4-Her’s help judge the event.  One said a “livestock show reunion”.

Fly control in cattle is about reducing fly populations, not elimination. The goal is to limit the negative economic impact that flies can cause. There are three main fly species that can economically impact pastured cattle and those are the horn fly, the face fly and the stable fly. Horn flies are responsible for significant economic losses. According to Dave Boxler of the University of Nebraska, economic losses associated with the horn fly are estimated at more than 800 million per year in the U.S. Those losses are due to decreased grazing efficiency, blood loss, reduced weight gains, and declines in milk production. University of Nebraska studies have shown calf weaning weights to be 10 to 20 pounds heavier when horn flies were controlled on the mother cows. Horn flies are small, about half the size of a housefly and they are blood feeders. Each fly will bite the animal and feed on blood 20 to 30 times per day. The economic injury or threshold level of horn flies is 200 flies per animal.

Horn flies spend most of their time on the animal. The female fly will leave the animal for a short period of time to deposit eggs in fresh manure and then will return to resume feeding. The most common and often the most convenient method of horn fly control is insecticide impregnated ear tags. The disadvantage of ear tag control is that there are horn fly populations resistant to the pyrethroid insecticides commonly used in the tags. In order to minimize and slow down resistance problems ear tags should not be put in until horn flies reach that economic threshold level of 200 flies/animal. Those horn fly ear tags should be cut out of the animal's ear in the fall of the year when fly levels decrease. Other control measures include backrubbers and dust bags, especially if they can be located in areas where cattle can have daily and consistent access to them. There are insecticide sprays and pour-ons that can provide between 7 to 21 days of control, but to be effective they must be applied on a regular basis throughout the fly season. There are also oral larvacides that prevent fly larvae from developing into adults. Although effective, the challenge is getting consistent, daily consumption. These products can work well for cattle in confinement situations or that are supplemented regularly on pasture, but are more difficult to use in rotational grazing systems.

In contrast to the horn fly, the face fly is a non-biting fly that spends significant time off the animal. This fly feeds on secretions, nectar and manure liquids. Face flies cluster around the animal's eyes, mouth and muzzle. Feeding around the eyes can cause tissue damage which opens a pathway for pathogens. The female face fly can vector the Moraxella bovis bacteria which is a primary pathogen for contagious pinkeye. Control of face flies can be difficult because of all the time that the fly actually spends away from the animal. As with horn flies, insecticide impregnated ear tags are a common form of control. Dust bags and oilers can provide effective control if, once again, animals can have consistent daily access to use of these options.

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