Bark is the outermost layer of tissue on a mature plant. It is made mostly of dead rectangular cork cells that fit tightly together.  It is pretty much watertight!

The bark on trees and shrubs is as distinctive and individual as the species that produce them.  Not surprising, there is a large variation in bark color, shapes and texture.  Aside from a broad range in visual characteristics – some features are clearly coming from a disease or disorder. Let’s see some examples !


The odd but normal


Odd looking but quite the norm are the corky “wings” of American sweet gum, the rough surface of elms, the flaking papery bark of river birches, and the peeling and cracking bark that falls off in olive, cherry, sycamore, crepe myrtle, Stewartia and Cornus kousa.

American sweet gum


River birch


Crepe myrtle


Cornus kousa


The certainly not normal and caused by an abiotic (non biological) disorder


Most certainly not normal are lignotubers – a mass of tissue full of small buds which sprout if the treetop is killed or damaged.

Burls occur naturally and are an adaptation to fire or other environmental stress.

Galls can be genetic, or from insects or disease.

Bark may peel and crack off as a result of sunburn. In winter, exposed trunk to warm winter sun rays may force cells to uptake water then freeze and crack at night or in sudden temperature drops. A sunken patch of tree bark is characteristic of sunburn.

Bleeding and gumming may occur as a result of a physical injury, pruning or severe water deficit. It may include the release of gums, resins, latex, sap or water.

Swelling is a result of additional growth to one particular area – causes include cracks under the bark, girdling, or stock grafts which may be smaller or larger.


Burl on birch tree


Typical gall tumor


The strange growths caused by genetics


Flowers may sometimes produce wide flat new growths which are called fasciation.  It is considered a mutation. Wound wood, or callus, is a woody tissue the develops around wounds indicating some previous damage. It retains it differentiated appearance and rarely reverts back to a normal looking bark.




Wound wood


The responses to a biotic (biological) disorder


Witches broom in roses ( buds clustering in one terminal branch) are from viruses.


Viral witches broom on rose


Swelling with oozing or chaff (small pieces of wood) is usually a biotic condition such as grubs – they dig out the wood to make a burrow and the resulting tissue can swell.

Gumming or oozing is usually caused by biotic agents – usually bacteria.


Extreme gumming on cherry is a sign of a disease


BEWARE  !!!  If the ooze is pink and smells like a really ripe sewer on a hot summer day – be prepared for the stink of a lifetime !  The culprit is Enterobacter cloacae hence its name – cloaca (an open sewer) – Yuck !


Stinky pinkish red slime !


If you see any strange things growing in your garden –

Call Plant Specialists TODAY !

We have experts that know what to do !

They are NYSDEC licensed applicators and can treat them too !!!

Don’t delay – the sooner the better !





Article written by our Staff Horticulturist, Peter B Morris, BSc, MSc, MBA

All photographs used with permission @SHUTTERSTOCK