University of Maryland Extension

Sycamore Anthracnose

Author: Karen Rane, Plant Pathologist, University of Maryland
Article originally appeared in the July 2013 HGIC eNewsletter

Back to shade tree anthracnose

Conditions have been perfect this spring 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

Sycamore AnthracnoseSymptoms 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?

At this point in time, nothing! Infections have already occurred, and the damage is done. Infected sycamores are now developing new foliage 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 severely cankered branches back to healthy wood) may help improve the appearance of infected trees, but it is not clear how much of an effect this has on the amount disease that will develop next year. Sycamores are infected with anthracnose to some degree every year, but the trees recover most of their canopy as the season progresses and they survive their yearly bout with this disease.

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