Fly Control in Dairies

Published on Fri, 05/07/2021 - 9:05am

Fly Control in Dairies.

 By Heather Smith Thomas.

 There are several types of flies that have negative economic impacts on dairies.  Milk production is reduced when cows spend extra energy fending off flies, and large fly populations can impact general health.  Flies can also transmit disease from cow to cow, and contaminate milk.

Control of flies is generally aimed at breaking their life cycle, to prevent new batches.  All flies pass through four life stages: egg, larva (maggot), pupa, and adult.  An adult house fly female can lay up to 1000 eggs, which are deposited on moist manure or any type of moist rotten or decaying organic matter. The eggs hatch in 10 to 12 hours and maggots feed on the moist material. 

Fly maggots mature in 4 to 5 days under warm moist conditions. Pupation occurs in the drier parts of the manure or other organic material, with adult flies emerging in 3 to 5 days. Under ideal conditions, a house fly can complete its life cycle in 9 to 14 days but this can be much longer in cooler temperatures. Although capable of flying several miles, house flies normally move no more than half to three quarters of a mile from their breeding sites.

House flies are a nuisance and health hazard, but flies that parasitize and feed on cattle often have more negative impact.  The three most significant pest flies are the stable fly, horn fly, and face fly. Stable flies develop as maggots in just about any decomposing organic matter, including soiled bedding and feed debris that accumulates wherever cattle are confined.  Horn flies and face flies develop in fresh cattle manure, and are a serious problem in pastured herds.  Horn flies, stable flies, and face flies on organic dairies can cause 10 to 30% reduction in milk production. These flies are irritating and can reduce pasture feed intake.  Face flies can spread pinkeye, and stable flies may spread disease from one animal to another.

House flies and stable flies are the most problem in dairy buildings but it’s not feasible to simply use pesticides for control.  The most successful way to combat fly populations is through integrated pest management (IPM) to maximize effectiveness of pest control while at the same time minimizing pesticide use and not harming beneficial insects that prey on flies.

Good sanitation/waste management is the basis of any control program.  Not only is it the most effective way to rid a facility of flies, but also most economical. Pesticides cannot eradicate flies when sanitation efforts are poor.  On average, a fly life cycle lasts from 10 to 21 days, so if you clean your barn weekly, you can break the fly life cycle. Each week, remove or spread out the materials where flies breed--including manure, spilled silage, moist hay, wet grain, etc.  Areas to focus on cleaning include calf hutches, holding pens, loafing sheds, paths to milking parlors and stalls.

Flies develop in moist manure or wet decaying organic matter.  Using sawdust instead of other materials for bedding reduces fly development. Spread manure thinly outdoors, so fly eggs and larvae will be killed by drying, or stack this waste and cover with black plastic.  The flies can’t get to it to lay eggs, and heat under the covering will kill any eggs or maggots already in it.

Eliminate silage seepage, wet litter, manure stacks, old wet hay/straw bales, and other organic matter accumulations that may attract flies; wet feed remaining in the ends of mangers breeds flies.  Provide drainage in barnyards. Use clean gravel and other fill to eliminate low spots. Proper grading and tiling can reduce wet barnyards. Keep water troughs and hydrants leak-free.

Calf hutches are perfect for flies because calves are confined there for long periods, they are moist, and calf manure is rich food for flies.  For a serious fly problem you may have to start with spraying, to get adult flies knocked down to manageable levels, and then clean out the manure beneath the hutches.  Once you get the fly numbers down to a manageable level, a strict sanitation program and possibly the use of parasitic wasps can keep the flies controlled.

To be successful in controlling flies, implement a program that best fits your operation. Reliance on a single practice or pesticide product is not the best approach. It works better to combine routine sanitation with a variety of pesticide strategies, such as baits, residual sprays, space sprays, and larvicides when flies are a problem.  Don’t wait for large fly populations to build up.  It is much easier and less expensive to keep fly populations from increasing at the beginning of the season than to try to control them after they reach high levels.  

Stable Flies
Typically stable flies are more problem where cattle are confined and fed (since they breed in rotting organic material), but the stable fly situation has changed significantly in the past 60 years.  Earlier they were mainly a problem around barns and pens.  Today, they have become a pasture problem as well, possibly because of large bales fed out on the pasture in feeders.  
A research project in Texas found more than a million stable flies in debris from each round bale site that didn’t get cleaned up off the pasture in the spring.  After feeding round bales, clean up those areas where hay and straw—mixed with manure—have been trampled into the soil.  If you can clean those up before fly season starts, and spread out those piles so they can dry out, or pile them in a proper compost area, they won’t be propagating flies.  If you put black plastic over those big piles it will bake the maggots.

Some regions have two stable fly seasons, in spring and fall, when there’s moisture.  In mid-summer, especially in southern regions, it can get too hot for stable flies.  When it gets to 95 or 100 degrees and everything starts drying up (especially in an arid environment) the stable fly population crashes.

But the main key is sanitation.  About 95% of the stable flies develop in less than 5% of the areas where there are cattle.  If you clean up those areas, it makes a big difference.  You might not need to clean the whole pen.  If you clean out from under and around feed troughs and debris from old hay/bedding, you have most of the problem solved.  There will often be thousands of maggots in a small area.  If you take samples from all over the pen you might find only find one maggot in every 10 samples, until you hit the areas of concentrated fly larvae.  If you clean those up, drain the wet spots, etc. you won’t have very many flies.    
It is vital to maintain a fly-free milk room.  Use extreme caution when applying pesticides, to avoid illegal residues in milk. If you must use pesticides, check with your milk inspector (to find out which ones you might be able to use), and always cover or remove milk and associated implements prior to spraying.

Non-chemical fly control methods are preferred.  Installing tightly-closed screen doors and windows leading to the milk room can reduce the number of flies that enter. Sticky tapes and light traps can catch any flies that sneak in through the screens.

Aggressive sanitation is most important.  The next line of defense is residual sprays applied to the outside and inside of buildings.  Use of larvicides, space sprays, and baits should be considered supplementary to sanitation and residual sprays.  Residual sprays can be applied to walls, ceilings, partitions, stanchions, posts, and other fly resting places. These sprays are more effective in stanchion barns than in open barns where landing and resting surfaces are minimal.

Surfaces vary in the amount of spray that should be applied; smooth surfaces require less spray than rough, porous surfaces. Thoroughly wet the surface to the point of runoff, using low pressures (80 to 100 pounds per square inch).  Avoid contaminating feed, drinking water, milking utensils, and milk rooms, and carefully follow label directions when using any pesticide.  Some premise sprays are not labeled for use in milking barns and parlors.  Some can be used in pens but be careful to not contaminate feed, water or foodstuffs.

Fly baits (attractant plus an insecticide) can provide temporary reduction of house flies but will not control stable flies. Baits should be placed in areas where flies rest, but away from feed, water, milk, cattle, and other animals. Baits work best where sanitation is very good so there is little completion from other food sources.

Baits can be applied following removal of all floor litter and manure. For best control, use baits liberally and repeat as needed.  It may be necessary to increase amounts when flies are multiplying, but check label for proper use directions. Baits are most effective when used in conjunction with other control measures

Use of oral larvicides is not legal in all states. These feed additives and boluses are not the answer to fly control unless used extensively.  They prevent development of flies in manure. They are not effective against existing adult flies and should be used in conjunction with regular manure cleanup. Supplemental fly control is needed where flies breed in manure from untreated animals or other organic sources.

Minimize Fly Resistance To Insecticides
Insecticides are categorized into numbered groups (1 – 28) based on how they work against insects.  Continual use of products from a single group against a certain fly species (for example the house fly or horn fly) can lead to reduced control of that species by all products in the group.  To minimize failures due to insecticide resistance, do not apply insecticides within the same group repeatedly, even when using different application methods (baits, residual sprays, knockdown sprays, etc.).  Rotate among groups during fly season. For example with house flies, you can alternate between Group 1 and Group 3 for residual sprays and use a bait from Group 4.

Fly Traps
Fly traps can capture large numbers of house flies but generally don’t reduce their numbers significantly. Ultraviolet light traps, bottle traps, and fly sticky strips can be useful, particularly in the milk room where pesticide applications are limited and fly numbers are low.

Horn flies can sometimes be reduced with fly vacuums.  The University of Minnesota West Central Research and Outreach Center (WCROC) dairy evaluated two methods (the Bruce Trap and Spalding Cow-Vac™) for controlling pasture flies.  Bruce traps and the Cow-Vac are compatible with organic dairying, because a trap can be positioned at the entrance to a milking parlor, where cows come and go.

To combat horn flies, W. G. Bruce, a USDA entomologist, built a box with one-way fly-screen baffles on the otherwise transparent sides, and walked fly-infested cattle through it to remove and capture their flies.  This simple design is known as the Bruce walk-thru fly trap, and different versions have been studied for horn fly control in various parts of the country. The fabric dislodges flies, which are drawn by light to the sides through baffles, where they are trapped and die.

The Cow-Vac can be placed at the entry or exit of milking parlor or barn.  As cows walk through, the Cow-Vac blows horn flies off the back, belly, face, flanks and legs into a vacuum system that collects them in a removable bag for disposal.  A 220-volt electrical outlet is needed, that can be reached by the 10-foot power cord. At the WCROC dairy, it took about a week to get cows conditioned to going through both fly traps.

During the summer of 2015, the researchers evaluated efficacy of the Cow-Vac in on-farm organic dairies to control horn flies, stable flies, and face flies. The study partnered with eight organic dairy farms in Minnesota, with herds ranging from 30 to 350 cows. The farms were divided into pairs by location and during the first part of summer (June-July) the Cow-Vac was set up on one farm and during the second period (August-September) the Cow-Vac was sent to its paired farm. Farms were visited once a week to collect flies from the CowVac, and to count and record flies on cows.

Horn fly numbers on cows were reduced by 44% on farm in the presence of a Cow-Vac compared to absence of a Cow-Vac.  Stable fly and face fly numbers were similar on each farm whether the Cow-Vac was present or absent.  

[Some of the information in this article is from Dr. Bill Clymer (retired parasitologist in Texas, Dr. Lee Townsend (professor emeritus, Department of Entomology, University of Kentucky) and Extension bulletins from the Ohio State University and the University of Minnesota]