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Virginia Cooperative Extension - Knowledge for the CommonWealth

The USDA estimates production losses due to insects at more than $2 BILLION

Dairy Pipeline: August 2004

Tina Horn
Extension Area Dairy Agent
Augusta County
(540) 245-5750 email:

The largest contributors are worms ($991 million), horn flies ($730 million), lice ($126 million), stable flies ($90 million), and face flies ($53 million). These losses are not always easy to see and often we see the effects but don't attribute them to insects. High parasite infestations cause reduced weight gain in replacement heifers, reduced milk production, increased mastitis and SCC, decreased disease resistance, and increase the spread of other diseases such as pinkeye.

Some steps to consider when planning a control program include: 1) Identifying the parasite. 2) Gathering information on its life cycle, hosting habits, timing of infestation, and economic thresholds. 3) Assessing the damage being caused and projecting damage that could be caused if nothing is done. 4) Estimate control costs. 5) Determine most effective and economical control method(s).

Chemical controls, biological controls, and cultural controls can all be used to reduce parasite population and a combination is most often advised and needed. Most of us are familiar with chemical controls (ear tags, sprays, pour-ons, etc.). However, we need to take step to reduce resistance to these chemical controls. Remember to rotate products, be conscious of timing of application, and in the case of ear tags don't tag them too soon and take them out at the end of the season. Biological controls can also be very effective and include parasitic wasps, predators, and pathogen. Walk-through fly traps and windbreaks are cultural controls. The least costly control is the removal of moist organic material used for breeding grounds for some insects. This includes spilled feed, silage leaks, manure piles, and rotting hay and straw.

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