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Managing Fly Population Levels with Milk Jugs

Taylor Leach

We’ve reached that time of year when thermometers start to skyrocket and rain gauges continue to overflow. While this hot, humid weather is an annoyance to both cattle and humans alike, it is the perfect condition for pesky insects like flies to thrive. 

Flies are not only a nuisance, but they can decrease an animal’s production efficiency. Flies cause cattle to expend extra energy fending them off instead of resting, feeding and milking. Other issues directly associated with fly pest problems on dairies include increased medication costs, veterinary costs, increased potential for disease spreading, and possible increased public complaints.

Common flies found on dairies include house flies, stable flies, and blow flies. These flies are commonly classified as “filth flies” as they like to breed in spoiled/spilled feed, bedding, decaying organic matter and manure.

While these insects have a relatively brief life cycle, ranging from 10 to 21 days, they can produce between 200 and 600 eggs, which can lead to high population levels in a short amount of time. These pests are typically located near moist organic matter in areas like calf hutches, feedbunks, water tanks and manure storage locations.

Below is a simple method to monitor fly populations that utilizes a common household item easily found on the farm.

Milk Jug Method – Using plastic gallon-sized milk containers, the “milk jug” method is an easy way to monitor fly population levels around the farm. To test this method, take a minimum of five plastic containers and cut a 2-inch hole on all four sides. Next, fill the jugs with fly bait and set/hang them in areas where you typically see insects. Leave these containers out for seven days before collecting and counting the number of flies. If the average number of flies exceeds 250, it may be time to apply insecticides.


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