By Jodi Zirbel
What does it look like?
A relatively new disease of redbay trees, laurel wilt (Raffaelea lauricola) is a fungus introduced into the tree by the redbay ambrosia beetle (Xyleborus glabratus). Brownish-black in color, the adult beetles are small and cylindrical, less than two millimeters in length, while the larvae are legless grubs that are primarily white in color with an amber head.
Host material and range
A non-native species, redbay ambrosia beetles were brought to the United States from Southeast Asia. Experts believe the beetles first arrived in the country near Port Wentworth, Ga., through untreated wooden packing material. The fungus continues to cause widespread, often fatal, damage to trees throughout the southeast coastal regions, including South Carolina, Georgia and Florida.
Upon attack, adult beetles use feeding tunnels to introduce spores of the laurel wilt fungus into the trees. The fungus provides food to the adult and larval beetles living in the trees. As the fungus grows, the tree’s food- and water-conducting systems are destroyed, which eventually kills the tree.
The fungus is believed to be spreading north into South Carolina, south into Florida and inland at the rate of about 20 miles per year. However, the fungus will move even more quickly to other parts of the country through infested firewood, wood chips and logs. In addition to feeding on redbay trees, the beetles have also been found to feed on pondberry, pondspice, sassafras and avocado trees.
Because the disease is so new, researchers are still determining effective management techniques. For now, experts are suggesting that landowners and loggers leave dead redbay trees rather than use the wood for chips or firewood. This will help to reduce the risk of beetles infesting other parts of the country. In addition, although most ambrosia beetle species attack stressed trees, redbay ambrosia beetles can attack healthy trees. For that reason, avoid unnecessary root damage from digging or improper watering practices.
While insecticide management options are still under investigation, research of other ambrosia beetle species from Tennessee State University indicates topical trunk treatments with dinotefuran, or the more common permethrin, may prevent ambrosia beetles from gaining entry into the tree. However, unlike other boring insects that feed within the tree’s xylem and phloem, the redbay ambrosia beetle has a single entry point and tunnels deep into the heartwood, limiting exposure to insecticide ingestion.
Because of the fungal nature of the disease, researchers are also investigating the effectiveness of fungicide applications. Although data is still being collected, experts believe fungicides (Triazole group) applied as a trunk injection may offer preventative hope to limit the spread of the laurel wilt fungus to healthy trees.
What can you do?
Monitor trees, especially those from the Lauraceae family, and if signs of the disease such as “toothpick frass” — are found, make traditional topical trunk treatments to adjacent trees most vulnerable for attack. Also, avoid root damage from construction in areas of infestation and check that irrigation systems provide the necessary amount of water for regional soils.
Jodi Zirbel is with Epic Creative, Wis. Article provided by Mauget, a leader in micro-injection and micro-infusion tree care. Contact Mauget or visit www.Mauget.com to learn more about laurel wilt and ambrosia beetles.