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 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.

Emerald Ash Borer Scouting

The way this client found me is a little bit strange.  He found my website by googling “bacterial leaf scorch” (I have articles posted about my experiences with BLS).  That’s what another “arborist” told him was wrong with his ash tree.  And that the disease would kill the tree, so he should remove it.  Well, ash trees have a few problems around here of late, but bacterial leaf scorch isn’t one of them.  Anyway, the tree didn’t look good and we talked about the true ash ailments – ash anthracnose (which the tree did have) and emerald ash borer (which hasn’t been found close to here yet).  In the end, he agreed we should inspect the tree for EAB, just to be sure.

Today, Ricky and Dave climbed the tree, and the one next to it, and checked it thoroughly.  Good news – negative for EAB.

The ailing ash

The ailing ash

Holes in leaves

Holes in leaves: from the ground you can’t see them in detail, can’t tell if it’s insect feeding damage; close up it doesn’t look like it. More likely caused by damage to buds from our late frost

We look for any clue - here you can see the wood pile contains ash firewood

We look for any clue – here you can see the wood pile contains ash firewood

hackberry emporer butterfly

While we were getting started, this hackberry emperor butterfly came by and took a liking to the minerals on Dave’s hardhat strap.  (Click the image to see a nice big version!)

Dave and Ricky

Dave and Ricky each went up a tree

a good, closeup inspection of the crown

…and did a good, closeup inspection of the crown.

If you have ash trees and are concerned about emerald ash borer now that it has been discovered in Bucks County, right now is the best time to have them checked.  This is the peak time for emergence of the adult insect.

DON’T PANIC! Your ash tree is going to be OK.

Have you noticed lots of leaves falling from your ash trees this past week (week of May 17th)?  Do the leaves look like this?

These trees will recover within the next couple of weeks, and will look fine for the rest of the season, with no permanent harm.  The culprit is a fungus disease called ash anthracnose, and the reason it is so noticeable this year is because we had a week of rainy weather just as the leaves were in their most vulnerable stage -partially expanded.  Once the leaves are fully formed, they will no longer be susceptible to the ash anthracnose pathogen, even if the spores are present and climatic conditions favor the disease.  Don’t let anyone talk you into treating this disease – sprays, injections or any other treatments will do absolutely no good.  In order to effectively treat this disease, the fungicide must be applied BEFORE the symptoms reach this point.  Because we can’t predict the weather in any given year, to treat a tree for ash anthracnose involves a fungicide application PREVENTIVELY, whether it will make a difference (wet spring) or not (dry weather at leaf expansion time).  Ash anthracnose poses very little impact on the health of a healthy ash tree.  It is mostly a nuisance (and perhaps a surprise) to the tree owner.  I do not recommend bothering with preventive sprays, unless the tree is already in precarious health or the tree is located where the leaf-drop nuisance is actually a real problem.