Livestock Fly Control

My cows have ox warble flies. What tools, practices, or products are available to certified organic dairies?

By Brian Baker

 Warble flies (Hypoderma bovis and Hypoderma lineatum) lay their eggs on the rumps and hind legs of cattle in the spring. When the eggs hatch, the grub larvae burrow under the skin. The burrowing damages the hide, irritates the cattle, and with severe infestations can cause a drop in milk production. Cultural management practices that may reduce fly populations include rotating pastures; reducing stocking density; temporary confinement when the adult stage warble flies are swarming; keeping hair short on the rump & hind legs where the eggs are attached; releasing egg & pupal parasitoids; and maintaining beneficial habitat (e.g. martin boxes). Each of these practices can bring down fly populations.

Using pesticide controls in addition to cultural management practices is also an option for dairies. Pyrethrum products labeled for control of flies and other pests in barns, dairies, milking parlors, milking rooms and poultry houses can be an effective warble fly control compliant for use in organic production. Pyrethrum though works mainly to kill the adults and deter the laying of eggs. Once the grub larvae have burrowed, sprayed pyrethrum (or most other non-systemic insecticides) won’t touch it. Several sources, report that rotenone is effective on the grubs subcutaneously when applied with a high pressure sprayer or brushed over the holes. With that said, EPA registrations for products that formulate with rotenone active ingredient that carried livestock use instructions were voluntarily surrendered in 2006. Systemic controls such as ivermectin, moxidectin, and to a lesser extent fenbendazole, are used to fight against warble flies on the subcutaneous layer. Of these three controls, moxidectin and fenbendazole remain allowed for use in USDA organic production. 

Revised and updated in August 2022 by OMRI Technical Director Doug Currier. This article was originally published in the Summer 2006 edition of the OMRI Materials Review newsletter.