Armillaria in oak trees - Ask Extension
Can armillaria in established oak trees be diagnosed objectively? What are the treatment options, if any? One of my neighbors received this diagnos...
Knowledgebase
Armillaria in oak trees #874851
Asked June 26, 2024, 4:59 PM EDT
Can armillaria in established oak trees be diagnosed objectively? What are the treatment options, if any? One of my neighbors received this diagnosis from your lab for one of her oak trees that fell down. Our home has 18 well established oak trees that appear healthy, but I'd like that confirmed. Your advice and recommendations are appreciated!
Washington County Oregon
Expert Response
Healthy trees in good soils will be more resistant to Armillaria. The disease spreads by root contact (healthy tree root contacts infected tree root) and spreading of soil, roots or wood fragments from infected areas. Sanitation by removal of infected soil, trees, stumps, and roots can reduce risk of spread.
If your trees are a good distance away from the infected tree(s), that will reduce chance of spread. There are no effective treatments for trees once they are infected.
For more information see: https://pnwhandbooks.org/plantdisease/host-disease/oak-quercus-spp-armillaria-root-rot
https://pnwhandbooks.org/plantdisease/pathogen-articles/common/fungi/plants-resistant-susceptible-armillaria-root-rot
https://hortsense.cahnrs.wsu.edu/fact-sheet/oak-armillaria-root-rot/
If your trees are a good distance away from the infected tree(s), that will reduce chance of spread. There are no effective treatments for trees once they are infected.
For more information see: https://pnwhandbooks.org/plantdisease/host-disease/oak-quercus-spp-armillaria-root-rot
https://pnwhandbooks.org/plantdisease/pathogen-articles/common/fungi/plants-resistant-susceptible-armillaria-root-rot
https://hortsense.cahnrs.wsu.edu/fact-sheet/oak-armillaria-root-rot/
Thank you!
One additional question: Could this "soil-borne fungus" be transported by normal water run-off (rain) from one home to another home? We have been told this is a possibility by an arborist, but I cannot see it mentioned in any of the above articles.
Again, thank you for your sharing your expertise.
Linda Williams
I have not found any reference to Armillaria spreading via water. Some other diseases (like Phytophthora) have a life stage that moves in water, but Armillaria does not. If the water flows overland and moves infected soil/root particles, perhaps that could spread the disease. Otherwise, the primary mode of spreading is root contact with infected material.
Thank you!
Your first link to PNW Handbooks contains the statement, "Natural oak-root infections will not threaten the native oak's life . . . unless the balance tips in favor of fungal growth and against root growth.
Question: If fungal growth eclipsed root growth, would this only be demonstrated by the above-ground symptoms noted in this article?
Question: Or would it also show up as decay within the wood of an affected tree from not receiving sufficient nutrients from the roots?
Again, my sincere thanks for your feedback.
Linda
Oak trees declining due to Armillaria along with environmental stresses are an example of fungal growth "eclipsing" root growth. Many trees can survive a long time with root disease, but environmental stresses from climate extremes or site development can tip the balance in favor of the fungus. In which case dieback of the foliage and eventually death of the tree can result.
Armillaria and some other fungal root diseases infect living tissue in the vascular cambium, which is the primary cause of dieback. But they also decay the wood, which can lead to breakage and failure of roots and the main stem. The infection of the vascular cambium impairs multiple functions (water and nutrient uptake from the soil, translocation of carbohydrates from photosynthesis) as trees are effectively girdled by the disease.
Armillaria and some other fungal root diseases infect living tissue in the vascular cambium, which is the primary cause of dieback. But they also decay the wood, which can lead to breakage and failure of roots and the main stem. The infection of the vascular cambium impairs multiple functions (water and nutrient uptake from the soil, translocation of carbohydrates from photosynthesis) as trees are effectively girdled by the disease.
