University of Maryland Extension

Sycamore Anthracnose

Author: 
Karen Rane, Plant Pathologist, Plant Diagnostic Lab
Blighted area along vein of sycamore leaf
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Sycamore Anthracnose

Conditions were perfect in spring 2013 for a severe outbreak of sycamore anthracnose, caused by the fungus Apiognomonia veneta (say that three times!). We have had many reports in the past of American sycamores (Platanus occidentalis) and London plane trees (a cross between American sycamore and Oriental plane tree with the scientific name Platanus x acerifolia) that show significant shoot blight and defoliation. The fungus overwinters in cankers from previous infections, and produces spores in the spring that are dispersed by rainfall to young developing shoots.

Symptoms

Symptoms include shoot dieback and blighted areas on leaves that usually run along the veins. In addition to the amount of rainfall, the severity of the disease is affected by spring temperatures during bud break through leaf emergence. If the average daily temperature at this critical time is below 55 °F, anthracnose infections will be severe. If the average daily temperature is 60F or above during this time, disease incidence will be greatly reduced. Conditions were so favorable this spring that even London plane trees, which are reported to be resistant to sycamore anthracnose, are showing significant dieback. Remember, resistance does not mean immunity – when environmental conditions are very favorable for the pathogen, some disease will develop in resistant plants.

What can be done when you see the symptoms?

At this point in time, nothing! Infections have already occurred, and the damage is done. Infected sycamores will develop new foliage later this spring to take the place of the initial growth lost to anthracnose, and temperatures will be warmer and therefore unfavorable for disease development on this new growth. Sanitation (raking fallen leaves and twigs, pruning out cankered branches back to healthy wood) can help to reduce the amount of reinfection. For high-value sycamores, there are a number of fungicides labeled for spray application, including thiophanate methyl (Cleary’s 3336 and others), chlorothalonil (Daconil) and copper products (Kocide and others), but these must be applied before bud break in order to be effective, and large trees are difficult to treat in this manner. Arborists in our area have successfully controlled sycamore anthracnose using trunk injections of the systemic fungicide Arbotect 20S. Injections are performed in late summer (early September) when trees are in full leaf, and protection can last up to 3 years.

May 2013
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