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Create a dairy fly control plan

Bill Clymer Published on 21 May 2010

A one-size-fits-all fly control plan for all dairies doesn’t exist. Each dairy has its own unique facilities and management, and each fly management program will have to be individually designed to meet the dairy’s specific needs. However, the one overall item that will generally result in the largest economic return for your investment is effective sanitation.

This includes not only manure management but also the elimination of any moist, decaying organic matter such as spilled feed, silage, rotting hay, etc. Remember that generally 90 percent of your dairy’s flies will be developing in less than 10 percent of its physical area; therefore, the elimination or cleaning up of those areas will greatly decrease your fly production.



The next item of major importance is to identify which pest flies are bothering your cows to determine the correct program to control them. Different types of flies may come from completely different sites or breeding areas.

Your tools for fly control can include, but are not limited to the following:

1. Sanitation – Eliminate or dry any moist, decaying organic matter.

2. Chemicals – Residual sprays can be used in conjunction with parasitic wasps, as long as fly larval development areas are not sprayed. Area-wide spraying kills the adult flies, and it also kills parasitic wasps, if used. Be aware that flies may be resistant to many products. Direct animal application (labeled pour-ons and sprays) will help reduce adult fly populations and can be used with parasitic wasps. Use only products labeled for use in dairies in your state.

3. Parasitic wasps – Coupled with good sanitation management, parasitic wasps provide an effective and economical way to keep the fly population in check. They occur in nature but cannot produce in sufficient numbers to control exploding populations of flies. Regular releases are required to maintain effective fly control. Wasps attack the pupal stage of the fly and kill it before the adult fly can emerge and lay additional eggs. Release should be started just before fly populations start to increase and continue through the fly season.


Like feed or genetics, there are many variables in fly parasites. Both species and emergence rates can be significantly different. The basic criteria for purchasing fly parasites should be how many parasites actually emerge from the quantity you purchase. Some species are much more effective than others.

4. Sticky tapes and traps – These help to keep the adult fly population reduced. Specifically designed traps are required for stable flies.

5. Baits – Baits help to reduce egg-laying adults and complement good sanitation. Baits are only effective against house flies and resistance can be a problem.

6. Feed additives – Several different types of products can be used in the feed that pass through the animal, killing the fly larvae in the manure. Most are effective in reducing the flies developing in the manure; however, some may be damaging to the beneficial insect population (parasitic wasps and dung beetles). Be aware there are many non-manure fly breeding areas (waste feed, silage, wet hay, etc.) that will continue to produce heavy populations of flies even if using feed-thru larvacides.

Some tips for dairy fly control are as follows:

Tip 1: Identify the fly (or flies) – Different types of flies may require different techniques for effective fly control.


Tip 2: Find the maggots – Look for larval development sites such as edges of the silage pit, spilled feed, manure, lagoon, wet decaying hay, under feed trough, etc. Dig in moist areas that are neither too wet or too dry to locate larvae. If maggots are found, try to dry the area out or remove it. If you are using parasitic wasps, put some in this area.

Tip 3: Don’t overlook spoiled commodities, calf hutches, silage pits or bags, leaks in augers, old wet hay, bedding pack, under and next to feed troughs, fence lines, etc.

Tip 4: Manage your manure and any other decaying organic matter:

  • Clean it – A clean environment eliminates most fly breeding areas, especially if done on at least a seven-day interval.
  • Move it – Haul it away from the dairy site at least a quarter-mile and at least every seven days.
  • Sink it – A fly larvae has to have a medium that is 40 to 60 percent moisture. If a film of water (no crust) stays on the surface of the manure in a lagoon, no flies will reproduce.
  • Pile and compost it – By stockpiling manure in one large pile, internal heating will prevent fly development except in the outer few inches of the pile. If possible, turn or till the manure at least weekly. A black plastic cover over the pile will eliminate nearly all fly development.
  • Dry it – In areas of low rainfall, spread manure thinly on crop areas. Running a harrow or screen drag around pens and pastures to break up and dry out manure is effective.

No two years are the same for fly control problems. Wet winters and springs will usually result in a much worse fly problem than ones that are dry.

All the previous items listed are tools that can be used in a fly control program. No one tool will provide the level of fly control that is desired in a dairy situation.

Costs of the various methods vary with dairy size, design and area involved and will range from zero to $3 per head per month.

Fly control is not difficult but a plan is necessary to make any program work. The main issue is understanding the proper techniques and having the support and understanding of the entire crew. Fly control doesn’t just happen. By properly training employees and ourselves, a cost-effective program can be put in place. There are no magic bullets for comprehensive fly control that will overcome poor sanitation.

There are several ways that a dairy’s fly infestation can be evaluated including speck cards, traps, fly counts on a specific surface for an allotted period of time (e.g., one minute), employee complaints, spouse complaints, the number of flies in the office, etc.

If stable flies are the problem, a drop in milk production, kicking cows in the milk line or loafing area, bunching, irritated animals, etc. will indicate that there is the problem.

Most producers will just know by observing the facilities and milk production.

One of the best ways to evaluate the program is to “put your shadow” on the dairy. At least weekly make a walkaround, digging into moist areas, looking for maggots and noting those areas that need to be cleaned up or dried out. Set up a checklist to make sure that those places are corrected by your next observation walk. Observe the number of adult flies in the dairy, especially around the calf pens and loafing sheds. If using sticky tapes, observe the number of adults being caught on a daily basis.

Fly control is not difficult, but it takes a concerted effort on the part of all employees and coordination by management to make it effective.  PD

For additional information in both English and Spanish click here to go to the Spalding Laboratories website.

Bill Clymer  

Bill Clymer
Senior Scientist
Spalding Laboratories