Sycamore anthracnose

What is sycamore anthracnose?

Sycamore anthracnose is caused by the fungus Apiognomonia veneta. UMass notes its older name was Discula platani. UMass says American sycamore can be highly susceptible, though natural resistance varies. London planetree often resists it, but some cultivars are susceptible. Colorado State says Oriental planetree is highly resistant.

The fungus lives through winter in twigs, branches and fallen leaves. In wet spring weather, spores spread onto new shoots and leaves. Infected shoots die quickly. On larger leaves, brown dead areas form along the veins. Leaves drop, and the tree may look like it never leafed out.

Colorado State says that if the average temperature stays below 55°F for two weeks after the first leaves appear, the shoot-blight phase will be serious. Little or no disease occurs above 60°F. A second set of leaves may come out from mid-June into July. UMass says repeated tip death gives the tree a right-angle branching pattern, and Colorado State notes clusters of dead and live twigs. UMass notes anthracnose adds to decline in trees already stressed by compaction, a restricted root zone, injuries or drought, and Oklahoma State says it may kill infected trees.

Symptoms and signs

• New leaves that wilt and die soon after they come out in spring, often mistaken for frost damage
• Brown dead areas along the main leaf veins
• Blighted leaves dropping in late spring
• Small cankers on twigs at the base of dead leaf clusters
• A tree that is slow to leaf out or looks bare into June
• Right-angle branching and clusters of dead and live twigs from years of tip death

Sycamore anthracnose identification: what to look for

• Symptoms: Newly emerging leaves wilt quickly in early spring. This shoot blight is often mistaken for frost damage.
• Symptoms: On larger leaves, angular brown spots and blotches form along the main veins, especially the midrib. Leaves drop early.
• Damage: Twig cankers at the base of blighted leaf clusters cause twig dieback. Colorado State says cankers can even kill larger branches.
• Signs: Tiny spore-bearing structures form along leaf veins and in the bark (UMass).
• Timing: Worst in cool, wet weather just after leaf-out. In bad years canopies stay sparse into June, and sometimes later.

Disease cycle

The fungus overwinters in twig and branch cankers and in fallen leaves. UMass says it stays active in twigs during mild fall, winter and early spring weather, killing buds. In wet spring weather, spores from cankers and old leaves spread to new shoots and leaves, which wilt and die. Infections make more spores that spread to nearby twigs, leaves and trees. A second crop of leaves may follow from mid-June into July.

When to look: Look from bud break through June. Damage is worst after a cool, rainy spring.

Sycamore anthracnose look-alikes

A few things get mixed up with it:

• Frost damage: Colorado State notes the quick wilting of new leaves is often mistaken for frost. Anthracnose leaves show brown areas along the veins and twig cankers.
• Powdery mildew: Makes a white powdery coating on planetree leaves, not brown blight along the veins. UC IPM notes planetree cultivars differ: some resist anthracnose and others resist powdery mildew.

How to manage sycamore anthracnose

Cultural control

• Plant resistant London planetrees. Colorado State and UC IPM name 'Bloodgood', 'Columbia' and 'Liberty'.
• Rake and remove fallen leaves and twigs.
• Prune out infected twigs and branches in fall or winter, and destroy or bury them (UC IPM).
• Reduce stress: water during dry spells, including dry winters, and avoid soil compaction and root damage. Colorado State says to base any nitrogen on a soil test.

Chemical control

UMass says fungicides are only warranted in select cases, such as young trees under stress. Where used, preventive sprays start as buds swell or open and repeat at label intervals until leaves are fully grown or the weather turns dry. Extension sources list active ingredients such as chlorothalonil, thiophanate-methyl, copper products, mancozeb and propiconazole, and Colorado State notes systemic trunk injection by licensed pesticide applicators. UC IPM says once symptoms develop or become severe, anthracnose can't be controlled that season. Use only products labeled for this use; the label is the law. Treatment of large shade trees should be done by an ISA Certified Arborist with a pesticide applicator license (see pesticide applicator license guide).

Use only products labeled for this disease and this site; the label is the law. For trees, work with an ISA Certified Arborist. If you hire someone to apply pesticides, make sure they hold your state’s pesticide applicator license; the rules for each state are in our pesticide applicator license guide.

Prevention

• Choose anthracnose-resistant planetree cultivars over American sycamore for yards and streets.
• Avoid irrigation that wets the leaves (UC IPM).
• Water trees during dry spells to limit stress.

When to call a pro

Call an ISA Certified Arborist if a large sycamore has dead limbs from branch cankers, or if a young tree is losing its leaves several springs in a row.

Related guides: Tree database: mature size and planting distance · Pennsylvania tree identification · Firewood rules by state · All pests and diseases

Questions about sycamore anthracnose

Similar pests and diseases