Chad's Garden: What is Wrong with the American Sycamore Trees?

After beginning to bud, bloom & unfurl leaves, now many Sycamores look sick & like they are dying by only partially foliating or foliating very, very little, as old blooms & leaves wither & fall off. What is going on?

Posted: May 9, 2019 9:26 PM
Updated: May 10, 2019 1:34 PM

Have you noticed how the forests are completey foliating now (whether sugar/black maple, oak, hickory, tulipree, etc.), but the American Sycamore look sick? 

This is especially true in the southwestern half of the viewing area where the trees were budding in late April.  In our north & northeast, the trees may not have advanced enough to show the foliage dying & falling.  I know it is pretty obvious here at Greater Lafayette.

After budding nicely, we have seen their young, unfurling leaves & blooms wither & shed, while some trees have shown very little replacement of this budding.  Many look like they have reverted back to winter dormancy.

Some show new, patchy foliation or scattered tufts of new leaves growing.

I captured this American Sycamore near the television station on May 8. 

This tree was budding nicely, then it new blooms & foliage withered away & fell off.  Now, it looks like it does in winter.

Note how the other trees behind it are all densely fully-foliated.

The period of weather April 24-May 5 is the culprit with only 2 of those 13 days not seeing rainfall.  Even when it did not rain, it was wet & damp with heavy dew in the mornings.

Also note the cold nights with 9 of the 13 days seeing lows in the 30s & 40s.  4 of the 13 mornings saw 30s with even a little bit of very light, patchy frost.

Wet, cold weather is the reason behind this.

The trees do this every few years during a cold, very wet spell.

Why?  Wouldn't they be adapted? (See below the weather records taken at WLFI at West Lafayette):

This is Sycamore Anthracnose disease.

It occurs typically in spring foliation during a period of persistent, cool, wet weather where the foliage is often wet for a long period of time & temperatures fail to rise above the 50s for many days (with overnight lows in the 30s & 40s).  It is often mistaken for frost damage.

The tree behaves almost as if it is needing water as the fresh new foliage & blooms wilt very rapidly, turn brown & fall, often leaving the tree naked like winter when all other tree species are green.  Cankers may also develop if the cold weather lasts too long with large twigs & branches even permanently dying back.  In a really rough year, parts of the crown may show complete die-back.

Two particular rough, rough years I remember as a kid in southern Indiana were 1992 & 1997 when large pieces of crown died in trees & it took until mid- to late-June for the trees to really foliate well.  Thing is, usually after this, there is rapid growth of new foliage at the base of the dieback.  Clusters of abnormal growth of twigs, like scattered small bushes in the trees (seen on Hackberry occasionally) called "witch's brooms" may develop, as well.

There appears to be some resistance to the fungus in some native Hoosier American Sycamore trees.  Some trees & local genetics are affected more than others.  I am working to collect seed & grafting wood from a couple of trees that seem resistant to it on the far southside of Lafayette.  I am going to try to head to this site in a few days to collect some seeds in the balls still left on the trees from winter.  I will try to get some grafting wood next winter.  These trees have actually continued to foliate very well & they are situated in a creek bottom that seems to allow cold, damp air to settle in.

So, this is a fungus.  Called Apiognomonia veneta, it cycles as overwintering in old diseased twigs, branches & even leaves.  The spores will proliferate when it is cold & wet.  The longer the period of such weather, the more spores that are produced.  New foliage that tries to grow may be re-infected if another unusually wet, cold snap occurs.

It takes until it warms up & dries out for infection to cease & trees to begin to try to re-foliate.

This infection can occasionally occur in the the fall if the leaves are still green & unseasonably cold, wet weather develops.  Symptoms are slightly different in that the large leaves develop big bown blotches & the foliage in parts of the tree begins to take on the appearance that it was scorched by fire or heat.  Twigs, branches or parts of the crown may suffer some die-back & the dry, crinkled leaves shed.

London Plane (Platanus × acerifolia) is a cross between the Oriental Sycamore or Planetree & the American Sycamore or American Planetree.  These two were planted next to each other & hybridized, most likely in London in the mid 1600s after the American Sycmore was introduced to Great Britain's Vauxhall Gardens by botanists.

It shows resistance to the fungus.  This trait tends to be carried when the two are crossed. 

Oriental Sycamore or Planetree is native from central Asia to Eastern Europe.

Closer examination of our native Hoosier American Sycamore will likely reveal more trees that more resistant to the fungus. 

Rather than using the hybrid London Planetrees, I really like good ol' native Sycamore with resistant to the fungus.

The good news is that most trees come out of this fine, but it takes a bit for them to re-foliate.

Pictures of symptoms...................

Image courtesy of Ohio State University:

Gradual recovery.

Image courtesy of University of Massachusetts.

Recovery after infestation.

Image courtesy of the University of Illinois.

Sycamore with really bad infection & permanent die-back of crown.............& gradual recovery.

Image courtesy of Missouri Botanical Garden.

Diseased foliage & newly-emerged fioliage in spring.

Courtesy of State of Delaware Forestry.

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