Stable Fly Activity Continues

Jonathan A. Cammack, Oklahoma State University Cooperative Extension Service State Livestock Entomology & Parasitology Specialist

 

It’s hard to believe that in the first week of July that stable flies are still an issue.

 

While near record rainfall across much of the state has been welcome for forage, hay, and other crop production, it has certainly contributed to pest issues in nearly every aspect of agricultural production, and livestock are no exception. We typically experience two peaks in stable fly activity during the year: one in the late spring/early summer, and the other in the fall, when daily temperatures stay below ~85°F. A cooler than average June across the entire state (Fig. 1A), coupled with higher than average rainfall (Fig. 1B), has helped stable fly populations proliferate, and remain longer than normal.

 

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Stable flies typically develop in the hay, manure, and urine mixture that occurs around round bale feeding sites. While you might have done a great job over the winter moving the placement of your hay bales to prevent the accumulation of that wasted hay and allow it the chance to dry out (Fig. 2), the immense amount of rainfall we have experienced so far this year has kept that material wet, and stable fly numbers up.


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In the absence of the hot, dry stretch that characterizes a normal summer, there are things we can do to help reduce stable fly numbers. Larvicide insect growth regulator (IGR) products such as Novaluron (ExhaltTM WDG) and Cyromazine (flynexx® granules) can be applied as granulars or sprays (dissolved in water) on top of these remaining patches of hay where the cattle fed on round bales. These insecticide products will dissolve and infiltrate into the stable fly breeding site (the decomposing hay, manure, and urine) and come into contact with or be consumed by larval stable flies, thus preventing their development to the adult stage. Alternatively (or better yet: additionally), you can periodically turn, till, or disc these areas of wasted hay to help this material dry out, and make the environment less suitable for stable fly development.

 

Due to the preferential feeding on the lower legs of animals, insecticidal ear tags are not typically effective for stable fly management.


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