Sycamore Anthracnose

Introduction

Anthracnose is the common name given to a group of fungal pathogens that cause dark, usually sunken lesions. The term anthracnose is from the Greek word for coal or charcoal. These are typically diseases of leaves, stems, or fruits. Anthracnose is the most serious disease of sycamore (Platanus spp.), but it can infect ash (Fraxinus spp.), elm (Ulmus spp.), maple (Acer spp.), and other deciduous trees and shrubs.  

Causal Organism 

The fungus involved in sycamore anthractnose is Apiognomonia veneta. The sycamore leaf is naturally fuzzy. Do not confuse this natural fuzziness with infection by anthracnose fungus. 

Symptoms

The sycamore anthracnose fungal organism attacks sycamore trees early in the spring, especially in cool, wet springs, causing a rapid wilt of newly emerging leaves. This rapid wilting is frequently misidentified as frost damage. Larger, more mature leaves develop a brown lesion along the main veins. Infected leaves often curl and eventually fall, littering the ground. This defoliation may be the most noticeable symptom of anthracnose on sycamore. Cankers often form on the twigs and branches at the base of blighted leaf clusters. Cankers restrict water and nutrient movement to the leaves resulting in twig die-back, chlorosis and scorch on leaves, and even kill larger branches. These cankers are active during wet cool springs and produce spores that spread to neighboring twigs, leaves, and other sycamore trees. 

Cankers also develop in larger branches, girdling and eventually killing them. Small, black fruiting bodies of the causal fungus appear in the discolored bark of dead twigs and branches. 

Repeated annual killing of twigs results in clusters of old dead twigs and live branches creating what are called “witches’ brooms.”

Weather Influences

Weather determines the severity of anthracnose. Frequent rains and cool temperatures promote the disease. If the average temperature during the two-week period following emergence of the first leaves is below 55 degrees F, the shoot-blight phase of the disease will be serious. 

Disease intensity decreases as the average temperature increases from 55 to 60 degrees. Little or no anthracnose will occur if average temperatures during this susceptible stage are above 60 degrees. 

Disease Management 

If trees are repeatedly affected by anthracnose, consider treatment. Apply sprays as buds begin to swell. During rainy springs additional applications are needed at 7 to 14 day intervals until conditions for this disease are no longer favorable (see Weather Influences above).

A second crop of leaves may be produced from mid-June into July after loss of the first set. Protect this second set of leaves with fungicide sprays if cool, moist conditions exist.

Fungicides registered for the control of sycamore anthracnose include chlorothalonil (Daconil Zn, Daconil Ultrex and Daconil Weather Stik. REI = 12 hours), thiophante-methyl (3336™ F and 3336™ WP. REI = 12 hours), and copper fungicides. Champion WP® and C-O-C-S® are copper fungicides approved for organic use. REI = restricted entry interval. Do not enter or allow workers entry into treated areas during this period following fungicide application. The REI varies with the copper product. Refer to labels for specific information. 

The recommended fungicides are usually available to homeowners at local nurseries and garden centers. Always read label directions. Labels may be updated yearly or more often. If the product label does not include anthracnose on ornamentals (shade trees), use an alternative product. For large trees that have been repeatedly affected by anthracnose, consider working with a professional for treatment. There are systemic fungicides that licensed pesticide applicators can inject into trees to prevent anthracnose.

Cultural Practices

Gather and destroy all fallen leaves and twigs. They will produce fungus spores the following spring if they are not destroyed. This will not eliminate the problem but will reduce the amount of fungal inoculum. 

Prune out all infected twigs and branches and destroy them. Cut out cankers in large limbs to reduce reinfection. Remove the dead, cankered tissue down to healthy wood. 

Dry winters weaken trees, increasing the effects of diseases. To reduce this problem, water trees once a month during winters without adequate precipitation. Water when the high temperature is above 40 degrees F and early enough during the day to allow water to soak in before nightfall. 

In the spring after leaf emergence, apply nitrogen around trees suffering from repeated attacks of anthracnose. This nitrogen application should be based on a soil test (see Homeowner’s Guide to Fertilizing Your Lawn and Garden). A yearly application of nitrogen will stimulate growth and help anthracnose-infected trees recover from loss of leaves, twigs, and branches. 

Disease Resistance

Plant species and cultivars that are resistant to anthracnose. The American sycamore (Platanus occidentalis L) is much more susceptible to anthracnose than the London (Platanus x acerifolia) and Oriental plane (Platanus orientalis). The Oriental plane, a shorter, less graceful tree, is highly resistant to anthracnose but rarely grown in the United States. The London plane tree (P. x acerifolia, synonyms P. x orientalis or P. hybrida) is a cross between the Oriental plane (P. orientalis) and the highly susceptible American sycamore (P. occidentalis). The London plane cultivars, ‘Bloodgood,’ ‘Columbia’ and ‘Liberty’ are resistant to anthracnose and are good choices for planting where the sycamore anthracnose fungus is a problem.

Anthracnose in Other Tree Species

Symptoms of anthracnose differ in different hosts, but all infected plants will have fruiting bodies, acervuli, which are cup-like structures that produce spores. These may be seen with the aid of a hand lens. The fungal pathogens that cause anthracnose are host-specific. For example, fungi that cause anthracnose in ash will not affect oak. Consider treatment for trees that are repeatedly affected by hracnose.

References

Dickman, M.B. 2001. Anthracnose. Page 43, in: Maloy, O.C., and Murray, T.D. eds. Encyclopedia of Plant Pathology, John Wiley & Sons, Inc., New York, NY. 

Hartman, J. 2001. Sycamore and planetree diseases. Pages 355-359, in: Jones, R.K. and Benson D.M. eds. Diseases of Woody Ornamental and Trees in Nurseries. APS Press, St. Paul, MN. 

Sinclair, W.A., Lyon, H.H., and Johnson, W.T. 1987. Diseases of Trees and Shrubs. Cornell University Press, Ithaca, NY. 574 pages. 

Influence of Environment and Inoculum Density on Penetration and Colonization of Sycamore Leaves by Apiognomonia veneta. Ammon, V., Graves, B. and Griffin, D. Plan Dis. 74:989-991. 

Reference: CSU Fact Sheet 2.930