Anthracnose

Maple Anthracnose- Gloeosporium apocryptum

Cool, wet weather in the spring is favorable for outbreaks of Maple anthracnose, caused by the fungus Gloeosporium apocryptum.

Symptoms are brown to black lesions along the veins of newly opening leaves. The lesions expand and can cover large areas of the leaves. Buds, leaves, twigs, and branches up to an inch in diameter may be killed. The infected leaves fall from the tree, causing the tree to expend additional energy to re-foliate.
Yearly infections by can weaken maple trees, predisposing them to other diseases and to insects. Good sanitation is critical in anthracnose control. All fallen leaves and twigs should be raked up and removed from
the planting. If the tree is small enough to make pruning practical, infected twigs should be pruned out of the canopy. A product containing chlorothalonil or mancozeb or copper may be applied at bud swell in the spring, and twice afterwards at 10-14 day intervals.

Ash Anthracnose

Susceptible cultivars of Ash are prone to Ash Anthracnose during cool, wet springs. This is a fungal disease caused by Discula fraxinea. The fungus overwinters on infected twigs, bud scales, and leaf litter. In the spring the spores are carried by rain and wind to newly emerging leaves and tender new twigs. Symptoms are black blotches on the leaves, leaf distortion, and small purplish-brown spots on the leaves. Premature leaf fall can be dramatic when petioles are infected. The tree will re-foliate almost immediately, but year after year of infection followed by having to produce another crop of leaves eventually weakens the tree and permits readier access for insects and other pathogens. Control begins with good sanitation. All fallen leaves and twigs should be raked up and removed. Resistant cultivars should be used when possible. Blue ash (Fraxinus quadrangulata) is very resistant.

Pumpkin (F. tomentosa) and American ash (F.americana) are less susceptible than green ash (F. pennsylvanica) and Chinese ash (F.chinensis). Preventative fungicides may be applied at bud swell in the spring followed by a
second application two weeks later. Products containing chlorothalonil, or copper may be used.

Sycamore Anthracnose

The most damaging disease of sycamore is Sycamore anthracnose, caused by the fungus Apiognomonia venta. Symptoms appear on new leaves as they unfold. Black to brown lesions occurs along veins, eventually
enlarging to cover the entire leaf. Twigs may be killed back 8 to 10 inches. Sunken cankers may develop on the main trunk and limbs.

During cool wet weather in the spring these cankers become active and produce spores that infect new leaf buds. Death of individual twigs and limbs occurs when a canker girdles them. Repeated twig death results in a witches broom type of growth, with a mix of dead and live twigs in clusters. Treatment begins in the spring as buds begin to swell. Fungicides containing chlorothalonil, or thiophanate methyl or copper should be applied at 7-14 day intervals as long as cool wet weather persists.

It is difficult to treat large trees. Planting resistant cultivars and species is the best option. The American sycamore is extremely susceptible. Susceptibility varies among cultivars of the sycamore, sold as London Plane tree with, Bloodgood, Columbia and Liberty having resistance to anthracnose.

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