Impact of Foliar Application of Acibenzolar S-Methyl on Rose Rosette Disease and Rose Plant Quality.

Rose rosette disease (RRD) caused by rose rosette emaravirus (RRV) is a major issue in the U.S. rose industry with no effective method for its management. This study evaluated the effect of foliar application of Acibenzolar S-methyl (ASM), a plant systemic acquired resistance inducer in reducing RRD disease severity on Rosa species cv. Radtkopink (Pink Double Knock Out®) under greenhouse condition, and the effect of ASM on plant growth under commercial nursery production conditions. ASM at 50 or 100 mg/L at weekly intervals significantly reduced RRD severity compared to the untreated control in two of the three greenhouse trials (P < 0.05). The plants in these trials were subsequently pruned and observed for symptoms, which further indicated that application of ASM at 50 or 100 mg/L lowered disease severity compared to the untreated control (P < 0.05) in these two trials. Plants treated with ASM at 50 or 100 mg/L had delayed incidence of RRD compared to the non-treated controls. Plants treated with ASM at 50 or 100 mg/L rate in all three trials either did not have RRV present or the virus was present in fewer leaf samples than untreated controls as indicated by RT-qPCR analysis. Overall, plants treated with ASM at 50 mg/L had 36-43% reduced RRD incidence compared to the water control. The treatment of two cultivars of rose, 'Radtkopink' and 'Meijocos' (Pink Drift®), with weekly foliar applications of ASM at three rates (0.5, 0.75 and 1.0 oz/A) indicated that ASM had no negative effect on flowering or plant growth at even the highest rate.