Sycamore anthracnose
Apiognomonia veneta
also called Plane anthracnose
A sycamore or plane that leafs out and then drops everything in May, with brown killed along the veins. It refoliates by July and is rarely in real trouble.
- Buds and new shoots killed outright in early spring, so the tree looks frosted or dead in patches.
- Brown, irregular blotches on expanding leaves following the veins rather than making round spots.
- Heavy leaf drop in late spring, often a second one, with the ground under the tree carpeted in green-brown leaves.
- Small cankers on the twigs, and a witches-broom of crowded shoots at the ends of branches after several years.
- A second flush of clean leaves in early summer, which is the normal course of it.
A fungus that overwinters in twig cankers and infects the emerging buds and leaves in spring. It is a close relative of the anthracnose that spots beans and tomatoes but a quite different disease in practice — a tree disease with a twig phase, driven entirely by the weather in the two or three weeks around bud break.
A cool wet spring, and particularly a run of days below 13 °C while the leaves are unfolding. A warm dry April gives a clean tree. American sycamore is hit hardest; London plane much less; Oriental plane hardly at all.
- Do nothing in summer; the tree has already refoliated or is about to.
- Rake up and remove the fallen leaves and twigs, which carry the fungus over.
- Prune out dead twigs and small cankers in dry weather during the dormant season.
- Water and mulch a young tree that has been defoliated twice in one year, which is a real drain on it.
- Thin the crown of a tree that has built up a broom of congested twiggy growth.
- Plant London plane or a resistant cultivar such as Bloodgood or Columbia rather than American sycamore.
- Give the tree an open site with air movement rather than a damp enclosed corner.
- Keep the litter cleared each autumn under a small tree.
- Feed and water a young tree well so it can afford two flushes of leaves in a bad year.
- Do not reach for a fungicide on a garden tree; the spray timing is at bud break, the coverage on a large tree is impossible, and the disease does not warrant it.
American sycamore above all, then London plane, Oriental plane, and to a lesser degree ash, maple, oak and dogwood with their own species of the fungus.
The Cottage Garden Companion — the gardener's apothecary at cottagegardencompanion.com