- Author: Chris M. Webb
The redbay ambrosia beetle (RAB) attacks healthy trees of certain species in the laurel family, including avocado trees. What makes this insect so dangerous is the disease-causing fungus it carries. The fungus, commonly called laurel wilt, is carried in sacs located in the beetle’s mouth. Once the beetle carries the fungus into the wood of a tree, the fungus moves through the water and nutrient transport system of the tree, plugging the flow of water and causing the tree to wilt. Leaves typically turn a reddish or purplish color. Most trees infected with the fungus die quickly.
RAB is about 2 mm long, and is dark brown to black in color. Female beetles fly and greatly outnumber the smaller, flightless males. Unfortunately there is not much to detect before the tree becomes infected. After infection RAB tends to attack the tree in large numbers and can leave sawdust tubes protruding from their bore holes.
RAB is native to India, Japan, Myanmar, and Taiwan. The origin of laurel wilt fungus is uncertain, but it is presumed to have been introduced with the beetle. Neither the beetle nor the fungus is known to be a pest in its native range.
This pest-disease complex is a big problem in the southeastern U.S. It likely arrived on infested wood packing material such as a crate or pallet used to ship commercial goods. It has spread quickly through Georgia, South Carolina and Florida. It has not yet arrived in California, but is expected.
What can you do to help? Don’t purchase firewood, tree trimmings or mulch from areas infected with RAB. Purchase only insect- and disease-free containerized avocado trees from reputable nurseries. Stay informed. If your tree shows signs of laurel with disease, please contact our office or the County of Ventura Agricultural Commissioner.
Photos of this pest can be found at this University of Florida website.
- Author: Chris M. Webb
I am sorry to have to report that we have another potential ecological and economic disaster coming our way. Much like the Asian Citrus Psyllid and Huanglongbing disease, this new threat is also a pest-disease complex.
Laurel Wilt Disease (LW) is caused by a fungus, which is carried by the Redbay Ambrosia Beetle (RAB). These beetles typically attack trees under stress (e.g. drought). The beetle bores into a tree carrying the fungus. The fungus in turn digests the wood disrupting the flow of water and nutrients. As the tree weakens it becomes more attractive to the RAB and is used for brood rearing and is attacked in mass. It only takes one beetle to cause the infection. Once a tree is infected it takes about 6 months to collapse. Unfortunately one of the hosts for the RAB is the avocado tree.
The initial detection of this disease in the US was found May 2002 in Port Wentworth (Savannah), Georgia. It has spread mainly along the coast of South Carolina, Georgia and Florida as of 2008. It is currently in the avocado orchards around Miami.
Much research is being done to help stop this destructive disease. While resistant trees are the subject of much of the research, we can all do our part to help stop the spread of the disease. This can be done in the following ways:
- Report any suspicious laurel trees to CDFA
- Voluntarily remove and destroy the tree
- Don’t move any symptomatic host wood from a site
- Don’t chip dead wood and use it as mulch around the yard
- For now, don’t purchase or obtain native Lauracae plants and avocado trees from an area known positive for the RAB-LW
- Leaving the tree in place will increase the RAB-LW infestations throughout your local area.
- Controlling the beetle may be impractical in the home landscape – it only takes 1 beetle to infest a tree.
Current control strategies are as follows:
Options for dooryard avocado trees
- Cut and burn the tree – not recommended because of the danger of burning and the requirement for burn permits, and various ordinances of local, state and federal agencies.
- Cut the tree down to the ground.
- Pile the wood or chip the wood of the tree, pile it on top of the tree stump and tarp this pile of wood to the ground; essentially composting the infested remains of the tree in-place
- Adding biosolids (e.g., manure), fertilizer, and water will speed the decomposition process
- Spray your chainsaws with bleach and water to disinfect it against the possibility of spreading LW fungus to other susceptible host trees.
