My ash tree has spots on its leaves. What is wrong?
Thanks to Johnny Twist for this week’s question! He notes that his Mexican ash has issues that he first noticed in late spring and that continued to worsen over the next couple of months.
From his photos, we can see that the small tree is surrounded by a vigorous rosemary bush. Johnny has been whacking away at the rosemary. He’s also treated the leave with Neem oil, without any improvement.
Well, this is, without a doubt, the year for splotchy leaves in Central Texas. After so many years of drought, with virtually no spring rains and temperatures going from 40 degrees to 90 almost overnight, microbes are definitely taking advantage of our very rainy, humid and cloudy months.
I turned to Paul Johnson, with the Texas A&M Forest Service, for advice. I noticed a bit of what appeared to be Anthracnose in one of Johnny’s photos, and Paul also pointed out some other areas where the leaf spots appeared to be a different fungus, Cylindrosporium.
In any event, fungal leaf spots such as these don’t really warrant any treatment with fungicides or other products. As Johnny noted, he’d already tried Neem oil, a natural fungicide, but hadn’t gotten any results.
The tree will eventually drop these leaves, and when it does, simply clean up the leaf litter and toss it, to remove the source of inoculum. I would also suggest continuing to prune back the rosemary surrounding the tree, or even removing it entirely. That would improve air circulation around the leaves of the tree, thus decreasing the possibility for future infection.