Technical Abstract: Sites where large round hay bales are fed to cattle during the winter have been identified as the primary developmental site for stable flies during the early summer in eastern Nebraska. Due to the high levels of microbial activity in these sites, the use of insecticides to control immature stable flies has proven ineffective. Previous studies have indicated that the primary emergence of stable flies from hay circles takes place in late May and early June. By mid July, these sites are no longer suitable for stable fly development. A method that disrupts development for as little as 3-4 weeks may effectively eliminate these sites as sources of stable flies. Solarization is a method of heating soil by covering it with clear plastic mulch. Soil temperatures of 50 - 60° C can be achieved with solarization. These temperatures are adequate to “sterilize” the soil, killing weeds, pathogenic bacteria, and nematodes. We evaluated the effectiveness of heating the substrate in hay feeding sites by covering them for 4 sunny days in late May with clear plastic on stable fly production. The sites will be monitored through the end of July to determine how long the treatment effects are realized and to determine the effect of solarization on the composting process in the hay circles.