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.

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.

Cedar Apple Rust

This morning as the rain was clearing out, I went to a clients property in Collegeville to quote some pruning work.  While there I noticed an eastern red cedar tree that was just beginning to “bloom” with the reproducing stages of cedar apple rust.

This common disease has a very interesting lifecycle : the fungus that grows as a leaf spot disease on apple trees produces spores which, when carried by the wind are deposited on cedars or other species of juniper, grow to form galls on the juniper twigs.  Then, after a spring rain when the temperature is suitable, the galls erupt into a brilliant orange jelly-like substance that is the spore producing stage on cedars.  This reproducing stage occurs magically fast after the rain, then only lasts a few days.  Spores from this fruiting body then infect the leaves of apple trees to complete the 2-stage lifecycle.

Galls just starting to expand

Galls just starting to expand

Fruiting body

Fruiting body