Saturday, July 10, 2010

Losing bark is natural for some trees

The loss of patches and strips of bark is natural for many trees and shrubs. The American Sycamore and London Plane trees exfoliate when the development of new bark pushes thin plates of older bark off the tree. This results in patches of green, brown and tan on the upper branches. Much less shedding occurs on the lower trunk of these Planes.

While the bark is a real mess for someone who owns or lives near a Plane tree, this happens only once each year. The bark can be collected, pulverized and used for mulch around your vegetables and flowers to help keep the soil cool and the roots happy. Running a lawn mower over the bark and capturing it in the lawnmower’s bag produces a nice mulching material. I would suggest you use an old lawn mower blade to do this so you don’t dull the blade you use to mow your lawn.

The American sycamore (Platanus occidentalis), aka buttonwood, buttonball-tree, American planetree and Western planetree, can be distinguished from the London planetree by the deep sinus at the base of the leaf blade as shown in the photo. The sinus of the London planetree [Platanus x hispanica (synonyms P. x hybrida and P. x acerifolia)] is much less distinct. Having said that, however, there is quite a bit of variation in leaf shapes even within a species.

The brown fruit balls also differ between the two species. The American sycamore’s one inch diameter seed balls are borne single or rarely in clusters hanging on slender stems from three to six inches long. The London planetree’s one-inch seed balls are typically in clusters of 2 to 4.

This photo shows clumps of dead branches. These clumps are called ‘Witch’s Brooms” and are the result of the fungal disease known as Sycamore Anthracnose (Apiognomonia veneta). This disease is most prevalent when we have cool, damp springs. Sprays can be applied to help control this disease but the best prevention is to never plant an American Sycamore.

“The American sycamore is much more susceptible to anthracnose than the London and Oriental planes. Due to this high susceptibility, planting of the American sycamore should be avoided. The Oriental plane (P. orientalis), a shorter, less graceful tree, is highly resistant to anthracnose but rarely grown in the United States. The London plane is a cross between the Oriental plane and the highly susceptible American sycamore (P. occidentalis). The London planetree cultivars, Bloodgood, Columbia and Liberty are resistant to anthracnose and are good choices for planting in Colorado” (

Note: Antracnose is a generic name given to any fungal disease that causes “characteristic limited, sunken, necrotic lesions… producing nonsexual spores in an acervulus.” Shurtleff, M.C. & Averre, C.W. III. 1998. Glossary of Plant-Pathological Terms, APS Press.

The name of the causal agent is Apiognomonia veneta, hence the reason for calling the disease by its common name “Sycamore Anthracnose.”

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