Sycamore anthracnose is a disfiguring disease of sycamore and plane trees (Platanus sp.) caused by the fungus Apiognomonia veneta.

Believed to be native to the United States it is found throughout the range of sycamores. The fungus spreads from infected to healthy trees as spores carried by the wind or rain.

Although not a fatal disease by itself, sycamore anthracnose often weakens a tree making it more susceptible to other pests and issues.

Sycamore anthracnose infects 4 distinct parts of the tree (twigs, buds, new shoots, and leaves). Keep this in mind when making diagnostic decisions in the field.

Susceptible Hosts (*denotes most susceptible)

* American sycamore P. occidentalis * California sycamore P. racemosa London plane tree P. x acerifolia Oriental plane tree P. orientalis

Pathogen

Apiognomonia veneta

Symptoms

• Necrotic patches along veins on leaves beginning in late spring (leaf blight)

• Defoliation beginning in early summer (leaf blight)

• Sunken cankers on 1-2 year old twigs (twig blight)

• Witches brooms forming at the canker sites on 1-2 year old branches (caused by cankers that girdle twigs and buds)

Signs

• None visible without magnification

Distinguish from Look-alikes

• Salt damage can cause marginal necrosis on leaves and cause witches brooms.

• Topping or pollarding can have a witches broom appearance

• Insects and powdery mildew can cause defoliation

• Look for cankers near witches broom

• Combine leaf spots, defoliation, presence of cankers, and witches brooms for correct diagnosis

The fungus that causes Sycamore Anthracnose causes cankers on the 1-2 year old twigs. These cankers serve as a source of inoculums (conidia) and cause repeated annual infections of young twigs which result in abnormal branching, loss of vigor, dieback of branches, and increased susceptibility to secondary diseases and insects.

Unlike foliar sprays, macro-infusion with Arbotect reduces the amount of inoculums in twigs over time. Foliar spray fungicide treatments are effective only for managing the leaf infection stage of this disease. Macro-infusion treatment with Arbotect can be made any time after mid-summer re-foliation until early fall.

Do not treat until infected trees have re-foliated from the current season’s infection, and avoid treatment after significant fall color is evident. Protection begins the year after application and lasts for up to three growing seasons.

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