Unusual disease outbreak in ash trees

Lots of local news coverage on the impending invasion of the emerald ash borer has many owners of ash trees alert for any unusual symptoms. So I was not surprised by the number of recent calls I’ve been getting about blighted ash leaves. Leaf drop in mid May is a common phenomenon, especially when it’s rainy when the leaves are just expanding. The culprit usually is a leaf disease called ash anthracnose which, while the symptoms can be alarming, it’s generally temporary and pretty harmless. But when I got two different calls yesterday-on Memorial Day- in which both clients used the word “orange’ in describing the symptoms- I realized something unusual was going on. Here’s what I found at a client’s property in Pottstown:

ash

ash rust2

ash rust

The disease is ash rust, Puccinia sparganioides. Spores from the disease on ash cannot infect another ash. They can only infect an alternate host, which is cordgrass which grows in salt marshes. Ash rust is common near salt marshes. But we are quite a distance from the nearest cordgrass marsh, making this a rather unusual event.

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3 thoughts on “Unusual disease outbreak in ash trees

  1. hello,
    I have small Ash volunteers in my Berwyn PA woods infected with this rust. Thank you for helping ID it. Do you think I should remove the saplings? They look like they have been sprayed with round – up.
    Regards,
    Janine

  2. Hey just came across your blog after searching google images for the past couple of days for ash leaves with similar symptoms and the pics show exactly what the ash trees around here look like (Worcester, PA). While there are several ash trees which have been thinning over the past coupe of years, most likely due to EAB, this fungus appeared out of the blue and has affected every ash tree we have come across, even the ones that are less than a foot tall. All my neighbors’ trees are infected as well as my parents, who live about two miles from here.

    I would be surprised if this is the kind of disease that spreads because it appeared out of nowhere and looks to have affected every ash tree around here. It’s as if if happened overnight because all the trees appear to be in the same stages of disease. This is fascinating and kind of disturbing at the same time. Wonder if there is anything we can do about this.

  3. Have you ever heard of this disease anthracnose making the tree shed a rusty colored fine powder on the ground?

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