Introduction

Flying insects are always a nuisance, but their activity definitely increases in the summer. New fly control options, where we are defining new as non-traditional, involve combining the use of chemical or organic methods with manure management. 

Feed-through fly control

The first new option is feed-through fly control. The fly goes through its life stages as egg, larva (maggot), pupa, and adult. Molting occurs between larval stages and in this time the fly must shed its cuticle. When manure is freshly deposited, adult flies lay their eggs which shortly thereafter hatch into larvae. Once in the manure, feed-through fly control chemicals that are added to feed or mineral rations pass out with the manure and work to prevent developing larvae from becoming adult flies. 

There are at least two products out there for feed-through fly control in horses: 

• SimpliFly™ by Farnam contains 0.24% diflubenzuron. Diflubenzuron is a chitin synthesis inhibitor and works by interfering with the production of chitin, a major component of the fly’s cuticle. This essentially stops the molting process of the fly which causes the fly larvae to die before reaching the adult stage.   
• Solitude IGR™ by Pfizer contains 2.12% cyromazine, which is also a chitin synthesis inhibitor. Because humans and other animals do not have insect growth hormones or chitin, these products are very safe to use and apply. Studies with Solitude show that it is safe for minnows, birds, and beneficial insects.   

For best results, these products should be fed as a top dressing on feed before the beginning of fly season (around late March) all the way until the first hard frost in the fall.    

Use of one of these products must be combined with a fly management program that includes cleaning up any feed or hay spills, and regular removal of manure and wet bedding, all of which provide the proper environment for fly breeding. Follow all label directions and store them in their original containers and keep them out of reach of children, pets, and livestock.  

If feeding these products, it is best to feed horses individually to ensure that each horse receives the correct dose of the product. 

Parasitic wasps

Parasitic wasps function by parasitizing fly pupa and prevent them from growing into adults. You can order them from a company such as Arbico or Organic Cowboy. A shipment will arrive approximately every three to four weeks. Pricing and amount shipped depends on the number of horses, what time of year you start the program, and other factors, such as severity of the fly problem and manure management.   

The shipment will contain parasitized fly pupae in wood shavings. Once a few have hatched, they should be placed into common breeding areas such as in your manure pile, under water troughs, at feeding sites, below bedding, and at the corner of pens and paddocks and cover them with dirt or manure to protect the pupa.  They will require periodic repopulation throughout the fly season; the company will ship you additional pupae as needed based on their evaluation of current conditions in your area.  

Organic fly control

An additional idea for organic fly control is microbial inoculant. Arbico has a product called EM-1™, which they state consists of naturally occurring microorganisms that work together to decompose organic matter in soils, manure and compost. 

A second organic fly control is the use of beneficial nematodes. Nematodes are roundworms that are found naturally throughout the world. They are used in fly control to attack fly maggots and other subterranean pests.  

They enter through the larvae’s body openings and emit a toxin that kills the larvae within 48 hours. They are shipped in a clay formulation mixed with water. This solution can then be put into common breeding areas identical to those used for parasitic wasps noted above, using a watering can, hose end, pump sprayer, backpack, or through misting or irrigation systems. 

Flies are pesky and a nuisance, but by exploring emerging ideas, along with good manure management, horse owners and enthusiasts can wage war in the battle on flies.   

Resources

Ogg, B. (n.d.). Low Toxic Fly Control for Horses. https://lancaster.unl.edu/pest/resources/flycontrolhorses%28332%29.shtml. Accessed 6/30/20.

Penn State Microbiome Manipulation Lab. (2019). Microbial Inoculants for Agricultural Soils – Potential and Challenges.  https://extension.psu.edu/microbial-inoculants-for-agricultural-soils-potential-and-challenges Accessed 6/30/20.  

The information in this document is for educational purposes only.  The recommendations contained are based on the best available knowledge at the time of publication.  Any reference to commercial products, trade or brand names is for information only, and no endorsement or approval is intended.  UConn Extension does not guarantee or warrant the standard of any product referenced or imply approval of the product to the exclusion of others which also may be available.  The University of Connecticut, UConn Extension, College of Agriculture, Health and Natural Resources is an equal opportunity program provider and employer.