Drought Influences Control of Parasitic Flies of Cattle on Pastures Managed with Patch-Burn Grazing

We compared the influence of patch-burn grazing to traditional range management practices on abundance of the most economically injurious fly parasites of cattle. Horn flies (Haematobia irritans), face flies (Musca autumnalis), stable flies (Stomoxys calcitrans), and horse flies (Tabanus spp.) were assessed at study locations in Oklahoma and Iowa, USA, in 2012 and 2013. Experiments at both locations were spatially replicated three times on rangeland grazed by mature Angus cows. Grazing was year-long in Oklahoma and seasonal in Iowa from May to September. One-third of patch-burn pastures were burned annually, and traditionally managed pastures were burned completely in 2012 but not at all in 2013. Because of significant location effects, we analyzed locations separately with a mixed effects model. Horn flies and face flies were below economic thresholds with patch-burn grazing but at or above economic thresholds in unburned pastures in Iowa. Pastures in Iowa that were burned in their entirety had fewer horn flies but did not have fewer face flies when compared with no burning. There was no difference among treatments in horn fly or face fly abundance in Oklahoma pastures. Stable flies on both treatments at both locations never exceeded the economic threshold regardless of treatment. Minimizing hay feeding coupled with regular fire could maintain low stable fly infestations. Horse flies at both locations and face flies in Oklahoma were in such low abundance that treatment differences were difficult to detect or explain. The lack of a treatment effect in Oklahoma and variable year effects are the result of a drought year followed by a wet year, reducing the strength of feedbacks driving grazing behavior on pastures burned with patchy fires. Patch-burning or periodically burning entire pastures in mesic grasslands is a viable cultural method for managing some parasitic flies when drought is not a constraint.