Location: Subtropical Horticulture ResearchTitle: Laurel wilt: A global threat to avocado production Author
Submitted to: World Avocado Congress
Publication Type: Proceedings
Publication Acceptance Date: 11/28/2011
Publication Date: 2/1/2012
Citation: Ploetz, R.C., Smith, J.A., Inch, S.A., Pena, J.E., Evans, E.A., Crane, J.H., Kendra, P.E., Hulcr, J., Stelinski, L., Schnell, R. 2012. Laurel wilt: A global threat to avocado production. World Avocado Congress. 186-197 In Proceedings VII World Avocado Congress. 5-9 September 2011, Cairns, Australia. Interpretive Summary: Laurel wilt is a lethal vascular disease of trees in the plant family Lauraceae, including avocado. It is caused by a fungal pathogen (Raffaelea lauricola) that is introduced into host trees by an exotic wood-boring beetle, the redbay ambrosia beetle (Xyleborus glabratus). The beetle was first detected in Georgia in 2002, and since has spread to six states in the southeastern U.S. Laurel wilt poses an imminent threat to commercial avocado production in south Florida, and a future threat to avocado in California, Mexico, Central and South America. Scientists at the USDA-ARS Subtropical Horticulture Research Station, in collaboration with the University of Florida, are conducting multidisciplinary research on the pest complex, including (1) evaluation of fungicides for laurel wilt, (2) screening for disease resistant avocado varieties, (3) determination of pathways for disease transmission, (4) identification of beetle attractants, repellents, and insecticides, and (5) assessment of host preferences. Information from these studies will be used by avocado growers and by state and federal action agencies engaged in monitoring programs for redbay ambrosia beetle.
Technical Abstract: Laurel wilt kills members of the Lauraceae plant family, including avocado. The disease has invaded much of the southeastern USA, and threatens avocado commerce and homeowner production in Florida, valuable germplasm in Miami (USDA-ARS), and major production and germplasm in California and MesoAmerica. Laurel wilt is caused by a recently described fungus, Raffaelea lauricola, which is vectored by an invasive ambrosia beetle, Xyleborus glabratus. Current research topics include: disease management with fungicides; identifying host resistance; vector mitigation with insecticides and repellents; host ranges of, and interactions with, the pathogen and vector; and transmission of R. lauricola via avocado seed, scion material, root grafts and pruning tools. Although highly resistant avocado cultivars have not been identified, screening work continues on additional cultivars and new germplasm. Effective fungicides (e.g. triazoles) have been identified, but cost-effective disease management will depend on improved measures for xylem loading and retention of these chemicals. Insecticides have been identified that reduce boring activity of X. glabratus and its attraction to avocado and other hosts, but much remains to be learned about their impact on disease management. Although the disease’s host range is generally restricted to American members of the Lauraceae, nonhosts that attract the beetle are known. Raffaelela lauricola rapidly colonizes avocado after infection, but to low levels; tylose and gel induction in the host, rather than xylem obstruction by fungal biomass, are associated with impeded water transport and symptom development. Seed and fruit from laurel wilt-affected avocado trees do not appear to be infected by R. lauricola.