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Managing Flies on Your Organic Dairy Farm

By Jessica Starcevich, Entomologist for Spalding Labs

Soiled straw bedding can produce both House and Biting Stable
flies. The reproduction is in the areas hooves don’t reach.

An old winter hay feeding area can be very productive Biting Stable
Fly breeding area.

Added February 11, 2014. As spring approaches, so does the coming fly season, which no dairyman looks forward to thanks to the mastitis, pink eye, and numerous other problems flies bring along. For organic dairy farms, this can be an especially challenging time of year. Unfortunately, there is no silver bullet for fly control, so developing an integrated pest management program is most effective for overall fly control. Every year, my associates and I visit over 100 dairies, both conventional and organic, to help them develop the best fly control program possible.

In this article, I’d like to share some of that wisdom so everyone can have a happier, more fly free summer. Because organic dairies have grazing cows, they get two different groups of flies. First, up near areas where manure and bedding accumulates, house flies and biting stable flies breed in abundance. Second, out in the pastures, the cattle will be bothered by face flies and horn flies. Because these flies breed in different environments, they require different approaches to control.

House Flies and Stable Flies

House flies cause a lot of the fly specks you see on walls, fences, and light fixtures. Although house flies don’t bite, they can spread bacteria which can spread disease among calves and contaminate milk. House flies breed in areas with manure and other rotting organic matter that stays damp, which includes calf bedding, areas around water and feed troughs, sick pens, holding pens, alleyways and crusted lagoons.

Stable flies look a lot like house flies, but they bite, mostly on the lower legs. Stable flies breed primarily in areas with decaying vegetation (that may or may not have manure), such as old winter hay, soiled straw bedding, and rotten silage. In fact, research at Texas A&M University has shown that over one million stable flies may develop from the residue of one round bale feeding site.

The most important method for controlling house flies and stable flies is SANITATION! Start by making sure to thoroughly clean up winter feeding and loafing areas in the early spring to kill off any overwintering flies.

A fly can go from egg to adult in just over a week, so cleaning weekly in the summer is important. Although calf bedding is one of the biggest breeders of house and stable flies, it’s important not to overlook smaller areas as well. The edges of alleyways, corners that are hard to scrap, and tires around the bases of posts can all breed a surprising number of flies because they’re often overlooked during regular cleaning.

This innocent looking little pile of spilled feed under a grain bin,
if it’s gotten wet and spoiled, can host thousands of fly maggots.
Check it and clean up regularly.

If you see fly pupae these could turn into a fly in hours.
Clean this area up ASAP.

Fly maggots still have to go through the pupae stage so these
won’t be flies for at least 3 more days.

Typically 5% of a dairy is producing 95% of its flies. Finding those hotspots is critical. The easiest way to find your fly breeding areas is to do a little scouting for maggots and fly pupae. Areas where you see fly pupae should be cleaned up first, because if they’re not already producing adult flies they will be within 3 days. If you see only maggots in an area, but no pupae, then you have a few extra days to get it cleaned up. Try to spread the manure thin so that it dries quickly, or pile it in one large pile to kill developing flies with the heat from decomposition.

Also, consider what materials you are using as bedding. House and stable flies breed more successfully in materials like straw and stover as compared to sawdust and sand. So, during the summer months, if you have access to sawdust or sand, a simple change in bedding material may help reduce your fly production.

In areas that are hard to clean effectively, or cannot be managed on a weekly basis, spreading fly parasites once a week during warm weather months may help. The better the sanitation, the fewer fly parasites are needed. Fly parasites are easy to use; just sprinkle some near all of the hard to clean areas and they will seek out and kill the fly pupae.

Fly parasites are an all-natural alternative to sprays, because they are a naturally occurring parasite of fly pupae. In nature, the fly parasite species often occur in low numbers, so they aren’t able to keep up with the faster breeding flies. By releasing fly parasites on a weekly basis, starting just before you have flies, you significantly increase their numbers so that you see much better fly control.

Face Flies and Horn Flies

Face flies and Horn flies can be some of the hardest flies to control on an organic dairy. Face flies do not bite, but like house flies are capable of spreading bacteria, making them an excellent vector for pink eye.

Horn flies are only about 1/3 the size of other pest flies and like to cluster along the shoulders, backs, and bellies of pastured cattle. Horn flies feed on blood and can quickly reach high numbers on cattle. Their biting causes cows to bunch together rather than graze and can also cause teat damage.

Face flies and Horn flies breed exclusively in fresh undisturbed cow pats in pastures, so one way to reduce their population is to break up cow patties about once a week. This can be done by dragging pastures with something like a screen drag to help break up and spread out the cow patties so that they dry quickly. Encouraging dung beetle populations can also help since they will quickly tunnel through and break up cow patties.

Fly parasites can kill Horn flies, but not Face flies. Putting them in pastures is a lot of work though, so we now suggest only using fly parasites in the barn areas, and use the CowVac (a unique system developed by Spalding Labs) to control Horn Flies. Place the CowVac on the path to or from milking and it will vacuum off the Horn flies and collect them in a bag for disposal. Because adult Horn Flies remain on a cow, rather than leaving to rest elsewhere, the CowVac is a very effective and lower cost means of reducing their population.

Fly season is coming, and unfortunately there is no way to stop it; however, by implementing these suggestions, both you and your cows can enjoy fewer flies this summer. Being Organic is not a handicap when it comes to good fly control. With a good IPM program, organic dairies can have better control than conventional farms that depend on heavy pesticide use.

Jessica Starcevich is an Entomologist for Spalding Labs (, a company offering products and information on fly control, including free phone consultations. Her phone and email are: 1-877-836-9746,

NODPA, 30 Keets Rd, Deerfield, MA 01342 FAX: 866- 554-9483 PHONE: 413 772 0444