Oak trees issue - Ask Extension
Can you help me identify what is wrong with my two oak trees? I am in the City and County of Denver.
Knowledgebase
Oak trees issue #873665
Asked June 18, 2024, 4:38 PM EDT
Can you help me identify what is wrong with my two oak trees? I am in the City and County of Denver.
Denver County Colorado
Expert Response
This could be anthracnose, which is caused by a fungus. The slight cupping of the affected leaves is one of the symptoms of anthracnose.
To be certain, I recommend you take a cutting to a plant diagnostic lab. We can't give a definitive diagnosis from the pictures alone. In the Denver area, you can mail or drop off a sample at the CSU Spur campus here in Denver. Here is their information about how to prepare the sample:
https://agsci.colostate.edu/soiltestinglab
Oak anthracnose does not usually kill a tree, especially if the tree is healthy. This publication from the CSU Extension agency has ideas for managing anthracnose:
https://planttalk.colostate.edu/topics/trees-shrubs-vines/1766-oak-anthracnose/
There is another fungus that affects oak trees called Oak Leaf blister. A symptom would be raised "blisters" on the leaves (a papery bulge on the top of the leaf) that are up to an inch long. These blisters later turn brown. The pictures you sent do not appear to have these type of blisters, but I recommend getting a diagnosis in lab to be sure. There is a cost for the diagnosis, but having a the correct diagnosis will help determine if treatment is necessary. Here is more information on Oak Leaf Blister from CSU: https://planttalk.colostate.edu/topics/insects-diseases/1449-oak-leaf-blister/
Healthy trees can often withstand both of these disorders so its important to maintain the health of the trees with correct watering and pruning. Removing and disposing of dead leaves in the fall can also help minimize the presence and spread of the fungus for the following season.
To be certain, I recommend you take a cutting to a plant diagnostic lab. We can't give a definitive diagnosis from the pictures alone. In the Denver area, you can mail or drop off a sample at the CSU Spur campus here in Denver. Here is their information about how to prepare the sample:
https://agsci.colostate.edu/soiltestinglab
Oak anthracnose does not usually kill a tree, especially if the tree is healthy. This publication from the CSU Extension agency has ideas for managing anthracnose:
https://planttalk.colostate.edu/topics/trees-shrubs-vines/1766-oak-anthracnose/
There is another fungus that affects oak trees called Oak Leaf blister. A symptom would be raised "blisters" on the leaves (a papery bulge on the top of the leaf) that are up to an inch long. These blisters later turn brown. The pictures you sent do not appear to have these type of blisters, but I recommend getting a diagnosis in lab to be sure. There is a cost for the diagnosis, but having a the correct diagnosis will help determine if treatment is necessary. Here is more information on Oak Leaf Blister from CSU: https://planttalk.colostate.edu/topics/insects-diseases/1449-oak-leaf-blister/
Healthy trees can often withstand both of these disorders so its important to maintain the health of the trees with correct watering and pruning. Removing and disposing of dead leaves in the fall can also help minimize the presence and spread of the fungus for the following season.
