Liriope’s Muse: Tree Care Tips from a Master Arborist
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Liriope’s Muse – Arborist Observation: Ambrosia Beetles, the vectors of Laurel Wilt
Our field Arborists have noticed an uprise in ambrosia beetle activity across the Houston area, especially on trees, like the Redbay and laurels. Many of the affected trees show tiny “pinhead” boring holes, light sawdust/tooth picking, and large patches of dieback or flagging in the canopy.
Ambrosia beetles have been a common presence in our region for the past few years, but the reason we are paying extra attention right now is because they are causing a devastating epidemic of Laurel Wilt across the Redbays and Laurels in our area.
And the one responsible? The Redbay Ambrosia Beetle or Xyleborus glabratus. It is the known vector of the fungal pathogen Laurel Wilt or Raffaelea lauricola. This fatal pathogen affects all species in the Laurel family, Lauraceae spp., including sassafras, laurel, and bay trees, but in the Greater Houston area, we have found it on the Redbay and Laurel trees.t up site-wide paragraph and title styles, go to Site Theme.
The inoculation process:
Adult Redbay Ambrosia Beetles bore into suitable hosts, typically one that is stressed from drought, over-pruning, physical damage, or herbicide damage, and lay their eggs beneath the bark in the sapwood of the tree. It is here that the beetles farm and cultivate the Laurel Wilt fungus (that they brought with) in the vascular tissue of the tree to serve as a food source for the growing larva. This food farming process creates anaerobic conditions in the sapwood and results in the production of ethanol and other alcohols, which helps to break down the sapwood and attract other beetles to the tree.
The cultivated fungus spreads throughout the tree’s trunk, blocking the flow of water and nutrients, ultimately choking the tree out and leading to the tree’s decline and death. Adult beetles then emerge with spores to search for new laurel trees as hosts and continue the disease cycle.
Once a tree is inoculated with Laurel Wilt, it can succumb in just a few weeks in severe cases or in just a few months.
All that said, Ambrosia beetles themselves aren’t typically fatal. In fact, a tree can survive many generations and seasons of ambrosia beetle attacks just fine. What’s deadly is the diseases that they bring with.
*The photos above show how devastating Laurel Wilt can be to a landscape, it also shows how it presents
in a tree's canopy via flagging*
Identifying Laurel Wilt:
Since this fungal pathogen affects the tree's vascular system, the symptoms present as drought stress. According to Texas A&M, key indicators of laurel wilt include:
- Mature trees are targeted before saplings.
- Leaves rapidly change from green to yellow within weeks, eventually turning brown, branches die, and branch tips begin to wilt.
- Toothpicking or compacted sawdust tubes across the trunk and major limbs indicating Redbay ambrosia beetle activity.
- Small beetle boring holes, about the size of a pinhead, visible on the trunk.
- Black-stained streaks on sapwood, just below the bark visible in trees that have recently declined, indicating laurel wilt infection.
- Trees that have died do not resprout.
Management :
At this time there is no cure for Laurel Wilt, unfortunately this disease has already taken out about 85% of all of the bay laurels in the southern United States, and is killing thousands of new ones each day and is showing no signs of slowing down. It is believed in just a few years if a cure is not found the Redbays, Laurels, and Sassafras trees will all go extinct.
So, the best thing that you can do for your trees is prevention, keeping your tree on a very strict pesticide regimen. In this case, an ounce of prevention is worth a pound of cure.
According to Texas A&M, Scientists are trying to create a resistant variety of the laurel tree, but at this time they have not been successful.
*The photo above is a cross-section of a tree that was killed by Laurel Wilt, you can see the fungus in the
top left of the sapwood*
Resources I found helpful in my research:
- https://tfsweb.tamu.edu/trees/tree-health/diseases/laurel-wilt/
https://pmc.ncbi.nlm.nih.gov/articles/PMC10744799/#:~:text=As%20the%20fermentation%20progressed%20during,enhancing%20fungal%20alcohol%2Dproducing%20metabolic%20activity.
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