Recovery plan for laurel wilt of avocado, caused by Raffaelea lauricola

Authors: PLOETZ, R.C. - University Of Florida; CARRILLO, D - University Of Florida; FRAEDRICH, S.W. - Forest Service (FS); HUGHES, M.A. - University Of Florida; Kendra, Paul

Submitted to: Office of Pest Management National Plant Disease Recovery System
Publication Type: Government Publication
Publication Acceptance Date: 10/21/2016
Publication Date: 12/1/2016
Citation: Ploetz, R., Carrillo, D., Fraedrich, S., Hughes, M., Kendra, P.E. 2016. Recovery plan for laurel wilt of avocado, caused by Raffaelea lauricola. Office of Pest Management National Plant Disease Recovery System.USDA National Plant Disease Recovery System. Homeland Security Presidential Directive Number 9 (HSPD-9). https://www.ars.usda.gov/office-of-pest-management-policy/npdrs/

Interpretive Summary: Laurel wilt kills American members of the Lauraceae plant family, including avocado (Persea americana), an important commercial fruit crop. The disease threatens commercial production in the US and other countries, and currently impacts the avocado industry in Florida. As laurel wilt spreads, the National Germplasm Repository for avocado in Miami (USDA-ARS) and commercial and backyard production in other states (e.g. California and Hawaii), US protectorates (Puerto Rico), and other countries are at risk. In the US, avocado production valued at more than $400 million yr-1 is threatened.Laurel wilt is caused by Raffaelea lauricola, a nutritional symbiont of an Asian ambrosia beetle, Xyleborus glabratus. Laurel wilt was first recognized around Savannah, Georgia in 2003, and has since devastated native populations of redbay (P. borbonia) and other native species in the family in the southeastern US. The first avocado tree was killed by laurel wilt in Jacksonville, Florida (2006), and soon after a southward swath of host trees began to die down the eastern flank of the state. In February 2011, the disease was confirmed in the Everglades in stands of native swamp bay (P. palustris), and by November of that year had spread to Florida’s primary commercial avocado production area (CAPA) in southeastern Miami-Dade County. Within 2 years, the disease had spread throughout the CAPA. Where insufficient or delayed implementation of control measures were used, the disease spread rapidly resulting in lost commercial viability and grove abandonment. Avocado production continues in Florida where laurel wilt has not spread and where expensive measures have been used to impede its movement. Excluding laurel wilt from healthy avocado orchards and managing the disease in affected orchards is a major, ongoing challenge. Laurel wilt has spread along the eastern seaboard of the USA due to a mobile insect vector, X. glabratus, the movement of wood infested with the insect and pathogen, and the presence of native and non-native plants that are susceptible to the disease and in which X. glabratus reproduces. Rapid spread has occurred where there are (were) high population densities of redbay and swamp bay. In avocado, the ambrosia beetles that disseminate R. lauricola are unclear. In addition, the pathogen likely moves via avocado root grafts, but dissemination via pruning equipment, fruit, seed or scion material is unlikely. Diverse disease management strategies have been examined for avocado, including host resistance and the use of fungicides and insecticides. To date, no highly efficacious and cost-effective measure has been identified. In the absence of such a measure, holistic considerations of host tolerance, chemical mitigation and cultural measures will be needed. In the latter situation, the prompt identification and removal of infected trees (sanitation) is needed to ensure that pathogen movement to adjacent trees via root grafts, as well as the reproduction of ambrosia beetle vectors, does not occur. Unexpected insights have emerged with nearly every new research finding on this disease.

Technical Abstract: Executive Summary Laurel wilt kills American members of the Lauraceae plant family, including avocado (Persea americana), an important commercial fruit crop. The disease threatens commercial production in the US and other countries, and currently impacts the avocado industry in Florida. As laurel wilt spreads, the National Germplasm Repository for avocado in Miami (USDA-ARS) and commercial and backyard production in other states (e.g. California and Hawaii), US protectorates (Puerto Rico), and other countries are at risk. In the US, avocado production valued at more than $400 million yr-1 is threatened.Laurel wilt is caused by Raffaelea lauricola, a nutritional symbiont of an Asian ambrosia beetle, Xyleborus glabratus. Laurel wilt was first recognized around Savannah, Georgia in 2003, and has since devastated native populations of redbay (P. borbonia) and other native species in the family in the southeastern US. The first avocado tree was killed by laurel wilt in Jacksonville, Florida (2006), and soon after a southward swath of host trees began to die down the eastern flank of the state. In February 2011, the disease was confirmed in the Everglades in stands of native swamp bay (P. palustris), and by November of that year had spread to Florida’s primary commercial avocado production area (CAPA) in southeastern Miami-Dade County. Within 2 years, the disease had spread throughout the CAPA. Where insufficient or delayed implementation of control measures were used, the disease spread rapidly resulting in lost commercial viability and grove abandonment. Avocado production continues in Florida where laurel wilt has not spread and where expensive measures have been used to impede its movement. Excluding laurel wilt from healthy avocado orchards and managing the disease in affected orchards is a major, ongoing challenge. Laurel wilt has spread along the eastern seaboard of the USA due to a mobile insect vector, X. glabratus, the movement of wood infested with the insect and pathogen, and the presence of native and non-native plants that are susceptible to the disease and in which X. glabratus reproduces. Rapid spread has occurred where there are (were) high population densities of redbay and swamp bay. In avocado, the ambrosia beetles that disseminate R. lauricola are unclear. In addition, the pathogen likely moves via avocado root grafts, but dissemination via pruning equipment, fruit, seed or scion material is unlikely. Diverse disease management strategies have been examined for avocado, including host resistance and the use of fungicides and insecticides. To date, no highly efficacious and cost-effective measure has been identified. In the absence of such a measure, holistic considerations of host tolerance, chemical mitigation and cultural measures will be needed. In the latter situation, the prompt identification and removal of infected trees (sanitation) is needed to ensure that pathogen movement to adjacent trees via root grafts, as well as the reproduction of ambrosia beetle vectors, does not occur. Unexpected insights have emerged with nearly every new research finding on this disease.