Why Sycamores Aren’t a Good Shade Tree for Most Home Landscapes

Why Sycamores Aren’t a Good Shade Tree for Most Home Landscapes

Marianne C. Ophardt
Washington State University Extension
Area Horticulture Specialist

The “true” sycamore is Plantanus occidentalis.  It’s also known as the American Planetree, Buttonwood, and Buttonball Tree.  This tree is native to North America.  It grows to a height of 75 to 100 feet.  Behemoth would be a good description of mature sycamores.  Sycamores are extremely susceptible to sycamore anthracnose (blight) and are also subject to problems with powdery mildew and sycamore lace bug. 

The London planetree (Plantanus x acerifolia) is commonly referred to as a “sycamore” in this our area, but it’s actually a different species.  It’s a result from a cross between the American sycamore (Plantanus occidentalis) and the Oriental planetree (Plantanus orientalis).  This London planetree is also excessively large, growing to a height of 70 to 100 feet.  This species is more resistant to sycamore anthracnose, but is still subject to the disease along with powdery mildew, sycamore lacebug, and the American plum borer.  There are several newer cultivars of the London planetree which are more resistant to anthracnose and should be considered when anyone decides to plant a sycamore.  

What’s good about the London planetree?  It’s a fast growing shade tree.  Unlike many other fast-growing shade trees, it’s not extremely weak wooded and thus isn’t prone to a lot of limb breakage in ice and snowstorms.  It’s easily transplanted and will do well in most soils, but prefers a deep, rich soil. It’s also tolerant of city conditions... air pollution, compacted soils, and drought.  It’s a very durable tree.  As a big tree, it also provides lots of wonderful shade in parks. 

Probably the most attractive feature of the tree is its bark.  As the tree matures, it sloughs or sheds pieces of the outer bark, giving it an interesting dappled pattern of olive green, cream, and light brown.   This random mosaic pattern is quite lovely and gives a special interest to the tree in winter.  If I was going to like the sycamore, it would be for its eye-catching bark. 

Now... on to it’s less desirable features.  One of the most obvious negative features is the size of the tree.  The London planetree is a BIG tree!  It grows to gargantuan proportions and is not well suited to the typical home lot or along a city street.  Growing to at least 70 feet or more in height and 80 feet or more in width, you need plenty of room for a London planetree.  Planted in the wrong place it can quickly come into conflict with utility wires, sidewalks, and driveways. Keep in mind that roots go out at least as far out from the tree as the tree is tall ... or more.

Because of its size and the lack of forethought when planting this tree, many tree owners opt to butcher their “sycamore” with topping or severe pruning when it gets too large for its space.  This pruning shortens the life of the tree and results in lots oftwiggy growth.  Attachment of this growth is weak, creating a hazard as the resulting branches grow larger and heavier.  Numerous fallen branches are often the consequence of windstorms and past topping of the tree. Open topping wounds lead to eventual wood rot.

Another problem with sycamores are their susceptibility to sycamore anthracnose , also known as sycamore blight.  This is a fungus disease that attacks sycamore buds, leaves, and shoots. The most typical symptoms are small to large brown dead areas along the main veins of leaves. Severe infections lead to leaf drop.  Infections in twigs and branches cause twig dieback. 

Cool, wet springtime conditions favor anthracnose development on sycamore. The disease is more severe when we experience a spring like we encountered this past April and May.  While it’s not “normal” for us to have repeated precipitation during the spring, it seems to be a frequently occurring weather pattern during the past five to ten years.  A disease that shouldn’t ordinarily be a problem with our “normal” climate, has continued to attack and disfigure area sycamores.  Repeated attacks seldom kill a tree, but they can sure give it a rather ugly, witches-broom or bushy appearance.

Fungicide applications to control the disease can be made early in the season when the buds swell and again when the bud caps begin to break.  However, control is often difficult because of the large size of the tree and the difficulty in getting good coverage. 

Powdery mildew is another disease problem that has been infecting some area sycamores.  It causes a distinctive white powdery fungus on upper leaf surfaces and green shoots. Leaves, especially those at the ends of branches, may be dwarfed, twisted, and completely covered by the fungus. The disease is usually worse on severely pruned trees which have lots of succulent leaf and twig growth. The powdery mildew usually becomes evident in late summer or early autumn.  Little real damage actually occurs to the trees other than the deformity of the leaves.  Control with applications of fungicides is not warranted unless the tree is of very high value or in a location where it serves as a focal point.  

As already mentioned, there are anthracnose resistant cultivars of the London planetree (a.k.a. sycamore.)  One cultivar, `Yarwood’ is very resistant to powdery mildew and fairly resistant to anthracnose.  ‘Bloodgood’ is very resistant to anthracanose.  `Liberty’ and `Columbia’ are two other cultivars that have been touted as being anthracnose resistant, but they’re apparently only resistant to eastern strains of the disease and not western strains. 

One of the positive features of sycamores planted in our area is that they aren’t often attacked by insect pests.  However, one little creature seems to be on the rise.  It’s the sycamore lacebug.  The lacebug is a tiny creature with clear lace-like wings.  It sucks the sap from the undersides of leaves causing astippled or speckled appearance on the top of the leaf.  The lacewings leave shiny black spots of excrement on thelower leaf surface. 

Visible damage from the lacebugs only seems to become evident late in the season.  In most cases it should not seriously harm the trees.  Trees should be kept in a vigorous condition with proper cultural care.  Stressed trees are more susceptible to attack and damage.  It’s especially important not to drought stress the trees during hot weather.  If control with a pesticide application seems necessary, an application of insecticidal soap would provide some control and still protect many of the natural predators.

Finally, this is a messy tree. Because the leaves are so large and numerous, they ’re a real nuisance in the autumn.  Add to this the litter from the numerous seed balls and twigs shed by the tree and you have a persistently messy tree.  In conclusion, it’s not advisable to plant a sycamore... but if you must, plant a resistant cultivar of the London planetree and be sure you have plenty of room for it to grow.