Effect of fungicides and hybrids on foliar diseases of grain sorghum in Arkansas

Abstract Two fungicides, pyraclostrobin and pyraclostrobin + fluxapyroxad, were evaluated on five grain sorghum hybrids to manage foliar diseases in a three-year field study. Anthracnose (leaf phase) caused by Colletotrichum sublineola Henn. ex Sacc. and Trotter was observed each year in Arkansas, while target leaf spot caused by Bipolaris sorgicola (Lefebvre and Sherwin) Alcorn was observed in 2016. Overall disease severity at growth stage 8 (hard-dough) was severe in 2016 and 2017, but low in 2018. The fungicides were similar in efficacy to control anthracnose and target leaf spot. Grain sorghum hybrids varied in susceptibility to anthracnose with Pioneer 83P99 and Pioneer 84P80 being susceptible compared to Dyna-Gro M73GR55, Sorghum Partners 7715, and Terral REV 9782. Pioneer 84P80 and Terral REV 9782 were susceptible to target leaf spot. A greater grain yield was observed on the anthracnose-resistant hybrids when foliar disease was severe (>20%) compared to susceptible hybrids. When anthracnose was severe (>20%), yield protection by a fungicide averaged 70% on the susceptible and 7% on anthracnose-resistant hybrids. Fungicides were more frequently profitable on susceptible hybrids when anthracnose severity was >20% than on the anthracnose-resistant hybrids. At best, fungicide profitability was inconsistent on susceptible hybrids where disease pressure was low (