Monterey Oak Leaf Discoloration

[southtx53]

Good afternoon,

I live in South Texas and have had these Monterey Oaks since the summer of 2022. They seem to be doing well, overall, and are growing taller every year, but I recently noticed some leaves that have fallen that were discolored. Nothing I have been able to find online on my own has been definitive as to what this could be. Any help to identify and treatment ideas would be appreciated. Thanks.

 

[pdqdl]

That is a leaf spot disease, most likely Septoria. Possibly Tubakia leaf spot or Anthracnose. Anthracnose is less a "spot" and more of a disease that follows the veins, so that seems unlikely.

In general, these diseases don't hurt your tree much except to defoliate and make them less attractive. By the time you see the spots, it is too late to treat, anyway. These infections can be somewhat prevented or reduced in severity, but usually are not worth the trouble to spray for. Watch it for now, compare to next year's outcome, and then decide if it is worth the money to do preventative treatments.

You should be able to find a local arborist capable of giving you an appropriate treatment plan, along with prices. Doing it yourself is seldom a viable option, because most people don't have the right equipment to get adequate penetration of the fungicidal spray into the canopy of a tree.

Here are some systemic fungicides that have shown promise in managing these leaf spot diseases:
Propiconazole:

A broad-spectrum systemic fungicide​

Effective against all three diseases: Tubakia, Anthracnose, and Septoria​

Often used as a preventative treatment​

Thiophanate-methyl:

Systemic fungicide with broad-spectrum activity​

Particularly effective against Anthracnose and Septoria​

May also provide some control for Tubakia​

Azoxystrobin:

A strobilurin fungicide with systemic and translaminar activity​

Effective against all three diseases​

Often used in combination with other fungicides for better resistance management​

Tebuconazole:

A triazole fungicide with systemic action​

Effective against Anthracnose and Tubakia​

May provide some control for Septoria​

Myclobutanil:

Another triazole fungicide with systemic properties​

Effective against Anthracnose and can help manage Tubakia and Septoria​

​

I don't ever recommend treating for leaf spot diseases as my customer base doesn't care enough about cosmetic appearances, so I cannot make any recommendations for you. My business doesn't revolve around my spray applications, so any advice I would offer for a treatment plan would probably be flawed.

I sprayed a bunch of trees two days ago, but that was to give them some leaf spots. Big, leaf dropping spots that would defoliate and kill the tree along the way. The plan was to wipe out the underbrush and understory trees, while leaving the bulk of the tree thicket intact so as to discourage homeless encampments.

 

[pdqdl]

Here's a promising treatment I found today:



From their sales blurb:
The active ingredient of MONTEREY COMPLETE DISEASE CONTROL
is a naturally occurring strain (D747) of the beneficial
bacterium Bacillus amyloliquefaciens. MONTEREY COMPLETE
DISEASE CONTROL BRAND also colonizes plant root hairs,
preventing establishment of disease-causing fungi and bacteria.

I'm a full believer of biological controls that have been evaluated, and this looks like it might mitigate your problem somewhat in the future, and won't likely cause a severe budget problem. I didn't price the product, but these things tend to be expensive to buy, and difficult to evaluate how well they work.

 

[southtx53]

Here's a promising treatment I found today:

View attachment 1187334

From their sales blurb:
The active ingredient of MONTEREY COMPLETE DISEASE CONTROL
is a naturally occurring strain (D747) of the beneficial
bacterium Bacillus amyloliquefaciens. MONTEREY COMPLETE
DISEASE CONTROL BRAND also colonizes plant root hairs,
preventing establishment of disease-causing fungi and bacteria.

I'm a full believer of biological controls that have been evaluated, and this looks like it might mitigate your problem somewhat in the future, and won't likely cause a severe budget problem. I didn't price the product, but these things tend to be expensive to buy, and difficult to evaluate how well they work.

Thank you so very much for this and the previous reply identifying the issue.