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.

Girdling root job

The client has 3 cherry trees in his front yard, and he wondered why they were not growing at the same rate.  He also noticed wounds on the trees that were not closing. The wounds turned out to be nectria cankers (a fungus disease).  The trees varied a lot in size, even though the same age.  All three trees had soil piled against the trunk and no visible trunk flare.  I couldn’t pull the soil away because ornamental grass was planted in it. There were no other obvious health problems above ground, so I suggested we blow away the soil from the base of the trunks and look for root system problems. Today the crew went to the property and did just that.  Using the airspade, they blew away the soil mounds and found roots encircling all the trunks.  This is surely the limiting factor for growth, and the stress from the trees’ reduced ability to conduct water and sugar reduces their ability to resist the nectria infection. Ricky called me to ask my advice about cutting the girdling roots.  What needed to be done was really radical surgery, and he was a little timid about it.  After all, we want to “first do no harm.”  So he sent me photos from his smart phone and I looked at them on my computer.  I reassured him that it was ok to cut the big roots.  Although the surgery would seem radical, there is no way the trees could live to be old without it. By the way – the big girdling roots in the perfect circle are probably the result of the tree having been raised in a pot.

girdling root

Update: Additional photos the crew sent me –

girdling root girdling rootgirdling rootgirdling rootgirdling root


Bacterial Leaf Scorch Update – Real Cases

You do not necessarily need to cut down your oak tree if you find out that it has bacterial leaf scorch. Yes, BLS is incurable.  But hey – so is diabetes.  If you find out you have diabetes are you going to go right to Dr. Kevorkian? Of course not!  Your doctor is going to tell you how to manage the disease.  And if you follow his advice you probably have a lot of good years left!

Here are some trees I’ve been watching for a while. All the photos were taken late in the growing season when the symptoms look the worst.

bls red oak paoli

Red oak, Paoli, tested positive 2007. Photo, Sept. 2010

This tree has some problems besides the BLS – old root and other injuries.  But the owner wants to keep it as long as possible.  It is not declining quickly.

bls row of red oaks valley forge

Row of red oaks, Valley Forge, photo Oct. 2010

These trees are healthy.  Do you see the gap in the treeline where the man is standing?  There was another oak tree there until 3 years ago.  It tested positive for BLS in 1992.  Before that, it was injured when the adjacent driveway was bulldozed.  Its health never recovered.  It stood diseased and declining for many years.  The trees right next to it were never affected although the spittlebugs and leafhoppers that can transmit the disease were surely present.

bls pin oak collegeville

Pin oak, Collegeville, photo Oct. 2010

This pin oak tested positive for BLS in 2003.  At that time, it was treated by trunk injection and prescription fertilizing to treat chlorosis (chlorophyll deficiency) NO antibiotics.  It looks like it is due for treatment again – see the yellow leaves?  But it’s hanging in there, not declining, no tip dieback.

bls pin oak norristown

Pin oak near Norristown, Oct. 2010

This tree tested positive for BLS in 1997.  It was treated with antibiotics and prescription fertilizer.  It had significant decline symptoms at that time, including tip dieback.  It has not been treated since, except for routine crown cleaning pruning.  It looks better than it did 13 years ago.  The owner is glad she kept it.

bls pin oak royersford

Pin oak in Royersford

This tree tested positive for BLS just last year.  The tree is full of sprouts because of bad pruning.  It is chlorotic because of soil chemistry.  This summer when the scorch symptoms appeared again the owner decided to invest in the treatments I suggested could improve its health.  We mulched as much of the root zone as he was willing to sacrifice from lawn area, to help preserve soil moisture.  This fall we will treat the soil with a prescription fertilizer treatment as per Penn State soil test results, along with a biostimulant.  Next spring I’ll evaluate leaf color and, perhaps, inject with micronutrient (iron) to treat chlorosis.  I will keep you posted next year with results!

What will happen to our oak trees in the future as a result of this disease?  Nobody really knows.  Here are some of the possibilities:

  • Some predict doom and gloom – a big percentage of red oak group trees will be killed.  Maybe, but I doubt it.  Remember that when you read a statement in a news article that says something like “90% of the trees tested in New Jersey have bacterial leaf scorch” that’s just the trees that are tested.  Nobody is testing trees that look healthy.
  • My guess is that we may find that the probability of infection is going to depend more on the individual tree’s genetics and health than just exposure to the bacterium.
  • Severity will probably vary from year to year.  Cold winters seem to suppress the disease.  Drought weakens the trees.
  • The oxytetracycline treatments used by some people really don’t seem to work.They definitely don’t  cure the disease.  But that doesn’t mean a better treatment won’t be discovered.  After all, Xylella fastidiosa is what causes Pierce’s disease in grapes.  It’s the same bacteria, though not genetically identical.  Xf  is a big problem for the grape industry.  And there is a lot more money for grape research than for shade trees.
  • I also predict that in many cases bacterial leaf scorch might end up being similar to a lot of other leaf diseases.  Like anthracnose of ash, sycamore and walnut, horsechestnut leaf blotch, scab of apples – more of a nuisance than a killer, especially if overall tree health can be  maintained.

We will learn more as the years pass.  I will watch these and other cases, and keep you posted on them as well as  on new developments.

GO TO MAIN ARTICLE on Bacterial Leaf Scorch

Bacterial leaf scorch is being exploited by opportunists. These two people avoided becoming victims.

Mrs. H and Mr. M from yesterday’s story have something else in common besides being surprised to find out the trees at their new houses had problems.  Both Mrs. H’s red oak and Mr. Ms pin oak have foliage that shows scorch symptoms.  Both could possibly be infected with bacterial leaf scorch (B.L.S.) (Xylella).

I think the causes of the bad appearance of the leaves on Mr. M’s tree are primarily abiotic – caused by environmental conditions rather than disease.  Mrs. H’s looks like bacterial leaf scorch.  But there is no way to tell for sure without a lab test.  Bacterial leaf scorch can’t be cured.  But BLS alone does not normally kill trees, at least not quickly.  We’ve only been able to reliably diagnose bacterial leaf scorch for about the last 20 years, and we still have more questions than answers about it.

But it’s been in the news a lot lately, and the news sensationalization of it has helped fuel a minor epidemic of fear.

Both Mrs. H and Mr. M solicited the help of other tree service companies besides mine.  Interestingly, both told me similar stories about their experiences.  Each was advised by at least one company that their trees were diseased and should be immediately removed.  And each had a company advise them to inject antibiotics into their diseased trees.  None of these companies suggested testing to find out if the trees actually had bacterial leaf scorch!  YOU CANNOT, WITH CERTAINTY, DIAGNOSE BACTERIAL LEAF SCORCH WITHOUT A LAB TEST!

I have a hunch that the companies that suggested removing the trees make a lot of their profit by removing trees.  And the ones who offer to inject them with antibiotics when they are symptomatic at the end of the growing season make a lot of their profit by selling snake oil pills.  Neither of these suggested actions is in the best interest of the trees or their owners.


Tomorrow I’ll share some case studies that will support my opinion that bacterial leaf scorch is not a death sentence.  I have been watching some cases for close to 20 years!

The perfect day for cedar-apple rust

Every spring, the first time we get the right combination of temperature and rain, the eastern red cedars “bloom” with the spore producing structures of cedar-apple rust galls.  YESTERDAY WAS THE DAY!  And this year, the phenomenon seems especially spectacular, with some trees that look like they are completely covered with fluorescent orange jelly.  Not surprising, considering how the wet weather last summer caused severe infestations of the disease on the alternate host, apple trees, where the spores that infect the cedars originate.

cedar-apple rust galls

cedar-apple rust

cedar-apple rust

More explanation of the disease and photos of the apple trees can be found at July 15, 2009 article.

cedar-apple rust

Does your oak tree look bad?

It might be bacterial leaf scorch.  OR IT MIGHT NOT.  There is NO WAY to be certain except by laboratory analysis using an immune response test.  Of course, it’s always important to correctly diagnose a problem before deciding how to treat it.

The wet weather we have experienced this year has provided favorable growing conditions for many leaf diseases of trees – in the case of oaks these would be oak anthracnose, Tubakia leafspot, leaf blister, and powdery mildew.  (If you are trying to diagnose the cause of your oak’s disease symptoms by looking at pictures on the internet be aware that oak wilt disease has not yet been found east of the Susquehanna River in Pennsylvania).

None of these leaf diseases (all caused by fungi) normally warrant control measures.  They are very unlikely to permanently impact tree health, and probably won’t be an issue next year unless we get another very wet growing season.

Bacterial leaf scorch is a different problem.  The bad news is it will not go away (even if treated with antibiotics – don’t be misled).  The good news is that BLS alone is not going to kill your tree, at least not quickly and not without the combined impact of other factors.

Bacterial leaf scorch has had a lot of media publicity in the past several years.  Unfortunately, it seems like a few unscrupulous tree care “professionals” have risen to the occasion, victimizing unsuspecting customers by recommending inappropriate, or bogus, treatments, or by recommending removal of trees based on strictly visual diagnosis.  Bacterial leaf scorch CAN NOT BE DIAGNOSED WITH CERTAINTY WITHOUT A LAB TEST.  And usually a symptomatic tree will be suffering from other ailments such as chlorosis, pest problems, previous moisture stress, root damage, soil problems, etc. that may actually be a bigger factor than the disease.

Don’t be scammed. Get an accurate diagnosis before you make a management decision.  If in doubt get a second opinion, preferably from someone who has no financial reward at stake, such as your Penn State Extension office.

More information about bacterial leaf scorch is available in my article on this site.

Cedar Apple Rust

A client in Collegeville asked me to look at her apple trees, which appeared unhealthy as the leaves were turning color and dropping off.

Viewed up close, the leaves display the orange colored lesions typical of cedar apple rust.


Nearby, at the property line, is an Eastern red cedar tree that is completely infested with cedar apple rust galls.

This is an interesting disease because it has a two year life cycle – spores (aeciospores) released in summer from the fungal fruiting bodies on the apple leaves travel through the air and when they land on Eastern red cedar or another susceptible juniper infect that host and produce galls that, in the spring, produce spores (basidiospores) that, in turn, infect leaves of nearby apple trees.  To see the fruiting galls on juniper in spring (an incredible sight!) scroll to the April 21 entry in this column.

I also noticed evidence of a canker fungus disease (possibly Botrosphaeria) and fireblight, a disease caused by a bacteria – Erwinia amylovora – both causing injury and death of branches.

If my client can convince her neighbor to remove the cedar tree (it is not a nice tree, either location or health-wise_ her apple trees will probably have much less leaf-spot problems in future years.

This winter we will do maintenance pruning on the apple trees, including removing the dead wood.  This should reduce the problem with the Botrosphaeria and Erwinia diseases.