Maintaining beef cattle in a dry lot is an alternative management system to traditional pasture or range beef production initially developed to offset the lack of pasture during drought conditions. Dry lot management continues to be used in situations when grazing is unavailable. There is one production issue that remains constant for any livestock producer in any management system, and that is flies. They are the face fly, horn fly, house fly, and stable fly depending upon the dry lot system utilized. Currently, two types of dry lot management systems are used, completely confined and semi-confined. A completely confined unit will be similar to a feedlot, whereas a semi-confined unit will allow cattle access to graze adjacent pastures on a regular basis. Let’s discuss the different flies that might be found in a dry lot system:

Horn Flies

United States livestock producers lose over $1 billion annually to the horn fly, making it one of the most damaging ectoparasites of cattle. Horn fly feeding causes dermal irritation, anemia, decreased feed intake leading to reduced weight gains, and diminished milk production. Horn flies can spread summer mastitis. Both male and female flies average more than 30 blood meals per day. Eggs are deposited in fresh manure and the entire life cycle can be completed in 10 to 20 days depending upon weather. Newly emerged horn flies can travel several miles searching for a host. Peak summer population numbers on untreated cattle can exceed several thousand per animal.

Face Flies

Historically, face fly activity has been observed east of the Nebraska Panhandle, depending upon climatic conditions. Face flies require areas with higher levels of humidity and rainfall than our other major fly species. Face flies are strong flyers and can move significant distances. If a confined dry lot is adjacent to an irrigated or native range pasture with grazing cattle, confined animals could be bothered by face flies. Usually the female fly is found feeding on various secretions from cattle and other animals: tears, saliva, nasal mucus, blood serum from wounds, and perspiration are all attractive to face flies. Males can be found on cattle, but generally feed on nectar from flowers or liquids from manure pats. The greatest impact of face flies is their capability to transmit pinkeye and other eye diseases to cattle.

House Flies

House flies develop in fresh manure or decaying organic matter mixed with manure, soil, and moisture; all of which can be found in and around a dry lot. These substrates are found next to feeding aprons, around feed bunks, under fences, and around mounds. House flies feed on organic waste material, which includes eye and nose mucous of cattle. When present in large numbers, house flies are annoying to cattle. The house fly can transmit more than 65 human and animal diseases. Mastitis, pinkeye, anthrax, typhoid fever, amoebic dysentery, tuberculosis, cholera, Newcastle disease and salmonella are some of the diseases affecting man and animals that are transmitted by these flies.

Stable Flies

The stable fly is a blood-sucking fly that feeds by piercing the skin and sucking blood. Stable flies remain on the animal long enough to obtain a blood meal (3 to 5 minutes), then fly off in search of shaded site to digest the meal. These flies can feed several times a day, depending upon weather conditions. The bite of the stable fly is very painful and irritating. When stable flies are abundant, cattle will bunch or seek water to stand in to avoid them. Energy normally used to convert feed to weight gain is used in fighting flies. Stable flies develop in decaying organic matter such as spilled hay or straw mixed with manure, spilled feed, and edges of hay piles. The most common locations are next to feed bunks, at edges of feeding aprons, under fences, and runoff drainage retention structures like debris-settling basins.

Management of Flies in a Confined and Semi-confined Dry Lots

Sanitation and Management

House flies and stable flies could be present throughout the fly season in both confined and semi-confined dry lots. Management of these flies first starts with sanitation. Clean-up spilled hay and other feed along edges of feed bunks, feeding aprons, and under fence lines where material is not trampled by cattle. Because flies develop quickly in warm weather, clean-up should be done every 7 days to disrupt the flies’ life cycle. Collected waste products can be either composted, compacted into a mound for future disposal, or spread as a thin layer on crop production sites. Poor fly sanitation management can lead to very high fly numbers that are difficult to control by other methods.

Horn flies and face flies may be a problem in the spring where pastured cattle are adjacent to a completely confined dry lot. This irritation can be short-lived, as horn flies and face flies typically do not develop in dry lot locations due to physical destruction of manure pats by penned cattle. Control products may not be required.

Cattle allowed to graze adjacent pastures to a semi-confined dry lot will deposit enough manure to produce horn flies and face flies. These flies will certainly be pests where cattle are grazing, but can also be an ongoing pest problem when the animals are in the dry lot.

Water Management

Maintaining a dry lot surface is important. Flies need moisture to complete their development, so removing water from lots will help reduce fly numbers. Dry lots should have enough slope to carry water away. Deep weeds and grassy vegetation should be mowed around a dry lot to remove resting areas for flies.

Chemical

Residual sprays are applied to areas where flies can pick up a lethal dose of the insecticide. The residual effectiveness of these insecticides is usually no longer than 2 to 3 weeks. House flies rest on sunny surfaces and tend to come inside buildings at night. Focus residual sprays on sunny surfaces such as fences, outside walls of buildings, and on the inside walls and ceilings of buildings. Stable flies rest on shady surfaces and are seldom found inside buildings. Apply residual sprays to resting sites, such as fences, feed bunks, and vegetation around dry lots. Apply residual sprays to the point of runoff, but do not allow puddles to form, and be sure to avoid contamination of water and feed supplies.

Area sprays provide a quick knock down of house flies and stable flies. An area spray should cover the entire dry lot and fly resting areas. These treatments can be applied with mist blower sprayers, low pressure sprayers and foggers. Since these treatments offer little residual activity, they need to be frequently re-applied.

There are a number of insecticidal baits labeled for use in Nebraska that can be useful for the reduction of house flies or blow flies. They do not impact other fly species.

Insecticidal feed additives/feedthroughs work by incorporating an insect growth regulator (IGR) in the feed. When consumed, the insecticide passes through the animal’s digestive system into the manure and prevents larval fly development. Stable flies and house flies can develop in many areas around a dry lot where fresh manure is not present. Therefore, feed additives may not provide complete house fly and stable fly control. These products can provide a degree of horn fly control that may be off-set by the immigration of horn flies from neighboring herds. Rabon, methoprene (Altosid), and diflubenzuron are three insecticides registered for this purpose, but methoprene (Altosid) is not registered for face fly control.

Dust bags and Oilers/Rubs can reduce horn fly and face fly numbers if used in a forced treatment situation, where the animal has to pass under them. Locate these devices in gate areas that separate the dry lot from the pasture.

Animal sprays can be applied using low pressure and mist blower sprayers. These types of applications need to be re-applied on a  regular basis throughout the fly season to achieve adequate fly control.

Pour-ons provide about 3 weeks of horn fly control, limited face fly control, and little impact on stable flies and house flies. Pour-on applications need to be re-applied throughout the fly season.

Insecticide ear tags work by releasing small amounts of insecticide as an animal moves its head. To achieve the maximum level of horn fly and face fly control, two tags should be applied to adult animals. Tag the calf as well, if face flies are present. Also, to enhance tag performance, delay tag application until the last week in May or first week of June. Insecticide ear tags have little impact on house flies and stable flies.

Biological Control

Biological control uses small parasitic wasps (pteromalids) to parasitize house fly and stable fly pupae. A female wasp will insert an egg into a fly pupae, upon hatching the wasp larvae then feeds on the developing fly. The number of parasitic wasps released depends upon the number of cattle present. Companies who sell the wasps can provide a formula or guidelines for calculating release rates and frequency. Make sure to purchase wasp species that parasitize both house flies and stable flies. When using this control method, sanitation and manure management is critical.

To maintain or enhance fly tolerance to current labeled insecticides, please rotate insecticide classes (Modes of Action) monthly for sprays, and yearly for insecticide ear tags, dusts and feed additives/feedthrough (IGRs) products.

For current Nebraska Control Recommendations refer to EC1550, Nebraska Management Guide for Insect Pests of Livestock and Horses

When applying any insecticide control product, please read and follow label instructions.

Interviews with the authors of BeefWatch newsletter articles become available throughout the month of publication and are accessible at https://go.unl.edu/podcast.