Amelioration of Tan Spot-Infected Wheat with Nitrogen

Abstract

Effects of nitrogen rate and form (0, 55, 110 kg/ha with and without nitrapyrin) on severity of tan spot of winter wheat were evaluated in southern Indiana. The Ryker silt loam soil was conventionally tilled, and wheat cultivars Auburn, Caldwell, and Blazer (resistant, moderately susceptible, and susceptible, respectively, to Pyrenophora tritici-repentis) were planted in a randomized, complete block design field experiment. Nitrapyrin inhibited nitrification, prevented overwinter loss of nitrogen, and increased the proportion of ammonium nitrogen taken up by the plants. The severity of tan spot decreased and yields increased as the rate of nitrogen increased. Disease severity was reduced further by inhibiting nitrification. The number of infection loci was similar in all treatments; however the rate of lesion development was markedly reduced as the nitrogen rate increased, and the pinpoint lesions developing on Blazer at the highest rate of stabilized nitrogen were simlar to those on the resistant Auburn. This research indicates that both the rate and form of nitrogen influence the severity of tan spot of winter wheat and that nitrogen management may provide a cultural control of this disease.