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) may all 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.

2.  Practice good garden sanitation by raking up and disposing of fallen leaves and twigs.

3.  Practice good cultural techniques to keep plants healthy and free of drought, and nutritional or injury-induced stress. Water trees twice a month during dry winters.

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

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

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

7.  Spray with a preventive fungicide such as lime-sulfur or chlorothalonil when leaves begin to emerge from buds. Reapply two or three more times at 7-10 day intervals. Fungicides are not effective after the leaves have been infected. Large trees may require the services of a certified arborist.

8.  Plant resistant species or cultivars. Oriental plane tree (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. In Strategy 7, the lime-sulfur mixture can be used in organic practices.

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.