A recent symposium in Florida described some of the results of research that has been conducted there over the last 18 months. This work is being done in Florida, but researchers across the country have collaborated, including people from California.
Avocado and other members of the laurel family are being studied, many of which are native to the southeast. Research has evaluated host response (plant size, inoculum threshold, cultivars), disease management (effect of various fungicides) and host volatiles for both attracting and deterring the ambrosia beetle carrying the disease-causing fungus.
The research group comprises over 30 individuals and the pathology work is being headed up by Randy Ploetz at the University of Florida. In the area of susceptibility, they have found that younger trees with less woody tissue (3 gallon trees versus 15 gallon trees) are less susceptible to the disease. For susceptible trees, it takes an extremely small amount of inoculum to cause disease. And there is a difference in cultivar response, with Mexican race types (‘Bacon’) being less susceptible than West Indian (e.g. ‘Simmonds’, ‘Russel’l, ‘Waldin’).
These preliminary results indicate that ‘Hass’ is intermediate in susceptibility to these two races of avocado.
They have also evaluated different families of fungicides and application methods – trunk injection, soil drench, foliar and trunk paint, and found that the triazoles (e.g., propiconazole, triadimenol, prothioconazole) as drenches and trunk paints can significantly reduce infection. None of these materials are currently registered for use on avocado, but could potentially be registered.
Lastly, Paul Kendra from USDA-ARS has been working with a group looking at host volatiles that attract and deter the ambrosia beetle. The idea is to develop attractants both for monitoring the insect, but also to attract and kill the insect. They have been successful in identifying at least two volatiles, manuka and phoebe oils, which will attract the beetle. These results will now allow them to determine what traps are best and at trap position in an orchard that would be most effective at attracting and killing the beetle.
A lot of money and a lot of people are being put into this research effort to control this lethal disease of avocado and other members of the laurel family.
Hopefully by the time the insect with its disease – causing fungus arrives in California we will have some good methods for controlling the damage. So far the beetle has been trapped in southern Florida, although at this time the disease has not been reported in avocado.
To follow the activities in Florida see: http://www.doacs.state.fl.us/pi/enpp/pathology/laurel_wilt_disease.html.
As of March 8, the red bay ambrosia beetle has been found in Miami-Dade County.