Sycamore Anthracnose

Overview

Sycamore anthracnose is a fungal disease that can cause leaf drop, twig dieback, cankers, and the sudden death of more than 90% of a tree’s new shoot growth. Although the disease is rarely fatal and trees will grow a second set of leaves, repeat infections will result in abnormal branching and will leave a tree stressed and more susceptible to other diseases and pests. American sycamore or buttonwood (Platanus occidentalis), London plane tree (P. x acerifolia), and Oriental plane tree (P. orientalis) all can be affected by sycamore anthracnose.

Symptoms and Diagnosis

Sycamore anthracnose is most common during the cool wet weather of spring and is often mistaken for frost damage. As new leaves unfold, they crinkle and turn brown, wilt rapidly, and fall. Dark and sunken dead areas form along the veins of older leaves eventually expanding to include the entire leaf. The tree may also develop cankers on twigs and older branches resulting in twig dieback and the girdling and death of the larger branches. Small black dots, the fruiting bodies of the fungus, may be visible. The clusters of dead twigs will result in abnormal branching such as witches’ brooms or as the twigs die, break, and fall, the tree will appear ragged. Reportedly, London plane tree is less susceptible to cankers than the American sycamore.

Life Cycle

The sycamore anthracnose fungus, Apiognomonia veneta, overwinters in diseased leaves and in cankers on twigs and branches. Spores are produced in spring and spread by rain. If the mean daily temperatures are 50 – 55 degrees F., the spores will germinate and the resulting infections will cause the death of new buds, shoots, and leaves. The disease will be slight or will not occur by late spring or midsummer when the mean daily temperatures are 60 degrees F. or greater and the tree will be able to produce a second set of leaves. The fungus may also infect twigs and buds in fall after leaf drop.

Integrated Pest Management Strategies

1.  Be patient. The tree may appear to be dead but will probably recover and develop new leaves and shoots as the season progresses.

2.  Practice good garden sanitation. Rake up and dispose of fallen leaves and twigs to reduce inoculum that can contribute to new infections.

3.  Practice good cultural techniques. Keep plants healthy by watering during times of drought, mulching, reducing injury-induced stress, etc.

4.  Prune out dead and diseased branches when possible. Diseased branches should be discarded. Disinfect pruning shears in a 10% bleach solution between cuts to avoid spreading the disease.

5.  Prune branches to improve air circulation. This reduces the length of time leaves are wet and thus susceptible to infection.

6. Apply a preventative fungicide. Fungicides with the active ingredient chlorothalonil, copper can be applied when leaves begin to emerge from buds. Repeat applications will be required. However, fungicides are not effective after the leaves are infected. Small trees that have defoliated several years in a row may benefit from a fungicide application, but is not practical to treat large trees owing to their size and potential for fungicide drift.   

7. Treat with a preventive systemic fungicide. This treatment may require the services of a certified arborist.

8.  Plant resistant species or cultivars. Oriental plane tree (USDA zones 7-9) and London plane tree cultivars, ‘Bloodgood’, ‘Columbia’, and ‘Liberty’ are less susceptible to the disease than the American sycamore.

Organic Strategies

Strategies 1 - 5 and 8 are strictly organic approaches. 

Pesticide Disclaimer: 

Always follow the product's label and ensure the product is effective against anthracnose. Not following the pesticide label before usage is a violation of federal law.