Fly Densities on Cattle Grazing ‘WW-B.Dahl’ Old World Bluestem Pasture Systems

Abstract

The decline in water supply for irrigation in the Texas High Plains is encouraging transition to drought-tolerant forages such as ‘WW-B.Dahl’ old world bluestem [OWB, Bothriochloa bladhii (Retz) S.T. Blake]. Cattle (Bos taurus L.) grazing this grass have been casually observed to host fewer horn flies (Haematobia irritans L.) ­but definitive data are lacking. Visual ratings (1-5 scale) were contrasted for fly densities on steers grazing two forage systems: grass-only (predominantly OWB) vs. grass-legume (OWB and alfalfa, Medicago sativa L.) in 2015 and 2016. Mean fly densities were not different between the systems in either year, but a date × system interaction in 2016 (P = 0.052) suggested a lower fly density for grass-only on 23 June. Horn fly densities were not consistently reduced on cattle grazing the OWB-dominant grass-only system, therefore our observations do not support anecdotal reports of significant deterrence of horn flies by WW-B.Dahl OWB.