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United States Department of Agriculture

Agricultural Research Service

Research Project: PROTECTION OF SUBTROPICAL AND TROPICAL AGRICULTURE COMMODITIES AND ORNAMENTALS FROM EXOTIC INSECTS

Location: Subtropical Horticulture Research

Title: Laurel wilt: A global threat to avocado production

Authors
item Ploetz, R. -
item Pena, J. -
item Evans, E. -
item Smith, J. -
item Inch, S. -
item Crane, J. -
item Kendra, Paul
item Hulcr, J. -
item Stelinski, L. -
item Schnell Ii, Raymond

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: April 5, 2011
Publication Date: September 5, 2011
Citation: Ploetz, R.C., Pena, J.E., Evans, E.A., Smith, J.A., Inch, S.A., Crane, J.H., Kendra, P.E., Hulcr, J., Stelinski, L., Schnell Ii, R.J. 2011. Laurel wilt: A global threat to avocado production. Meeting Abstract. abstract.

Interpretive Summary: 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, Raffaelela 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.

Technical Abstract: Laurel wilt kills American members of the Lauraceae plant family, including avocado (Persea americana). The disease threatens commercial avocado production in Florida, as well as the National Germplasm Repository for avocado in Miami (USDA-ARS). Elsewhere in the US, major (California) and minor commerce in the fruit (Texas, Hawaii and Puerto Rico) could be impacted if the disease continues to spread. Laurel wilt is caused by a recently described fungus, Raffaelea lauricola, which has an Asian ambrosia beetle, Xyleborus glabratus, as a vector both in Asia and the USA. X. glabratus originated in Asia and was reported for the first time in the Western Hemisphere in May 2002 in Port Wentworth, GA, a maritime port near Savannah. Shortly afterwards, laurel wilt was observed in the vicinity on redbay, Persea borbonia, a dominant component of Coastal Plain forest communities in the southeastern USA. Redbay has been devastated in the ensuing epidemic, and a separate recovery plan for it and other native forest suscepts has been written. The first avocado trees were killed by laurel wilt in 2006 in Duval County, FL, and the disease has been documented on avocado as far south as Brevard County, FL. Virtually all commercial avocado production in Florida is centered in Miami-Dade County, ca 200 km south of Brevard County. In February 2011, laurel wilt was confirmed on swampbay, P. palustris, in Miami-Dade County, about 3 km north of the nearest commercial avocado production area. In general, American members of the Lauraceae are more susceptible to the disease than are those from the beetle’s Asian home range. Host and X. glabratus interactions are less clear. Scant information is available on the extent to which lauraceous and non-lauraceous taxa serve as hosts and reservoirs for the vector and pathogen. Laurel wilt has spread due to its mobile insect vector, the movement of infested wood, and the presence of native and non-native plants throughout the southeastern USA that are susceptible to the disease and on which the vector reproduces. Rapid spread has occurred where there are high population densities of redbay and swampbay (some taxonomists do not distinguish these species). In avocado, movement of the pathogen by root grafts is probable and by pruning equipment is possible; the possibilities of movement via fruit, seed or scion material are under investigation. 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) before emergence of brood will probably play a significant role; sanitation will rely on rapid and specific means by which laurel wilt could be diagnosed.

Last Modified: 4/23/2014
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