2018 ASHS Annual Conference

Commercial roses are susceptible to many viral diseases including rose rosette disease and rose mosaic virus disease. Between these two diseases, rose rosette disease is currently a major issue in the U.S rose industry. Rose rosette disease symptoms often appear as leaf distortion, rapid elongation of the branches, severe thorn proliferation, flower mutation, decreased vigor, and death of the plant. Currently, there are no effective methods for reducing the severity of rose rosette disease. Improving host resistance using a plant systemic acquired resistance (SAR) inducer is a potential management strategy, but needs to be evaluated against rose rosette disease. Acibenzolar S-methyl (ASM, Actigard) is a SAR inducer that activates the host plant’s salicylic acid pathway that stimulates plant immune defense mechanisms. The objectives of the study were to evaluate the effect of ASM on plant growth and development under commercial field nursery conditions, and to assess the effect of ASM in reducing rose rosette disease severity under greenhouse conditions in the absence of the insect vector (eriophyid mite). In 2016, two cultivars of Rosa L., ‘Radtkopink’ (Pink Double Knock Out®) and ‘Meijocos’ (Pink Drift®) (N=160), were treated weekly for 12 consecutive weeks with foliar applications of ASM at three rates (0.5, 0.75 and 1.0 oz/A). Continuous weekly applications of ASM at even the highest rates were never fatal to any individual of either rose cultivar. Flowering of either rose cultivar was unaffected by ASM treatment (P=0.05). Other plant parameters were also studied and will be reported. In general, this study has shown ASM is safe for use on roses undergoing containerized nursery production. Foliar application of ASM at 50 mg/L and 100 mg/L significantly reduced rose rosette disease severity compared to the untreated control in two of the three greenhouse trials (SNK, P=0.05). Based on this information, field studies on the impact of ASM to reduce rose rosette disease severity will be a top priority for ongoing research.