Effect of Propiconazole on Laurel Wilt Disease Development in Redbay Trees and on the Pathogen In Vitro
Albert E. Mayfield III, Edward L. Barnard, Jason A. Smith, Shawn C. Bernick, Jeffrey M. Eickwort, and Tyler J. Dreaden
Abstract: Laurel wilt is a vascular disease of Lauraceous plants caused by a fungus (Raffaelea spp.) that is vectored by a recently introduced, nonnative ambrosia beetle (Xyleborus glabratus). The disease is devastating to redbay (Persea borbonia) trees in forests, parks, and residential landscapes in the southeastern United States, and management strategies for reducing its impact are needed. In this study, the systemic fungicide propiconazole completely inhibited mycelial growth of Raffaelea spp. in vitro at concentrations 0.1 parts per million (ppm) or greater and was fungitoxic at 1 ppm or greater, whereas the fungicide thiabendazole was less inhibitory. None of the ten mature redbay trees that received root-flare injections of propiconazole developed crown wilt symptoms for at least 30 weeks after being inoculated with Raffaelea spp., whereas nine of ten untreated control trees wilted in more than one-third of their crowns. Propiconazole was retained in the stem xylem for at least 7.5 months after injection but was more frequently detected in samples from trees injected 4.5 months earlier and was not well detected in small-diameter branches. Results suggest that propiconazole may be useful in preventing laurel wilt in redbay, but limitations and questions regarding duration of efficacy, rate of uptake, and efficacy under different levels of disease pressure remain.
Keywords: Ambrosia beetle; fungicide injection; laurel wilt; Persea borbonia, propiconazole, Raffaelea; redbay; thiabendazole; vascular disease; Xyleborus glabratus