Current recommendations for control of Laurel wilt and its ambrosia beetle vectors in Florida's commercial avocado groves.
Laurel wilt (LW) is a lethal vascular wilt disease of woody plants in the Lauraceae family, caused by the fungus Raffaelea lauricola (Rl). Introduced into the U.S. in 2002 and detected in Florida's avocado production area in 2012, LW has caused the death of more than half a billion redbay trees and 140,000 avocado trees worth an estimated $46.2 million.Raffaelea lauricola is dependent on ambrosia beetles (AB) for dispersal. In avocado groves Rl is associated with several native and exotic ambrosia beetles. These beetles occur in large numbers and usually colonize trees that are physiologically stressed. After trees are inoculated by AB, Rl can spread through root grafts. Long-distance spread of the disease is by movement of beetle infested wood products. To date, no avocado cultivars (scions or rootstocks) have shown tolerance to Rl. Symptoms of LW begin as green leaf wilting in one or more sections of the canopy, followed by leaf desiccation, stem and limb dieback, and ultimately tree death; frass tubes are a sign that AB have bored into the tree. The pathogen moves rapidly through the tree resulting, in obstruction of the water conducting tissue (xylem) caused by the host tree's attempts to contain the spread of the fungus by forming barriers/eliciting the formation of tyloses. To date there is no cure for the disease. Current recommendations to contain the disease include early detection, complete tree removal and destruction (chipping) of infected trees and then applying insecticides to the trunk of trees within one acre of the removed trees to reduce AB populations. Prophylactic fungicide injections, applying formulations of the biological mycoinsecticide Beauveria bassiana (entomopathogen) to the entire orchard in late winter/early spring, and pruning to improve light levels within the tree canopies, are also recommended. In the absence of cost-effective control measures for LW, the current strategy to maintain avocado production in South Florida is to replant trees that are lost to the disease and to keep investing in research to find a long-term and sustainable solutions.