During rainy seasons and towards the end of the Summer we get several calls and emails from customers asking about small brown circles and brown spots that have started appearing on their Red Oak leaves. The brown circles can be irregular and will have a faint light brown/ cream colored halo around them.
WHAT CAUSES THESE BROWN SPOTS?
The cause of these brown spots is a fungus called Tubakia dryina, aka Tubakia leaf spot. All oaks trees are susceptible but it’s most commonly seen in Red Oaks. The Tubakia fungus overwinters in infected branches and dead leaves. Tubakia is also spread easily during rainy seasons.
WILL THIS HARM OR KILL MY TREE?
The good news is that Tubakia does not harm the tree and is only a cosmetic disease. It can make the leaves unsightly, but it will not kill your tree.
WHAT CAN I DO TO TREAT IT?
We do not recommend any fungicides or chemical treatments since it’s just a cosmetic issue. Over spraying trees can lead to weakening the trees and to trees becoming immune. It’s very similar to when people take antibiotics, and become weakened. What you recommend is that when the leaves drop in the Fall you can rake them all up and dispose of them. Although chemical treatments are not recommended you can use a broad spectrum fungicide as a preventative measure in early Spring right before the leaves bud out. If a tree already has Tubakia leaf spot then it’s too late to be treated and you have to wait for the infected leaves to fall off.