Spots on Leaves, Browning, Early Death
Anthracnose - Also known as blight and scorch, anthracnose is the most serious disease of sycamores, and to a lesser degree their planetree cousins. It is caused by a fungus which is stimulated by frequent rainy weather and cool temperatures. Symptoms become obvious early in the spring when individual or small clusters of leaves suddenly turn brown and die before they fully emerge. Later, developed leaves show triangular dead spots between their veins. Then cankers, or sunken infected spots with raised edges appear on twigs and leaf stalks, girdling them, thus killing them. They drop and the tree is defoliated for a time during the early summer until a second flush of foliage finally appears. The severity of an attack is linked to temperature. Infection is most severe when temperatures linger between 50 and 55°F while leaves are emerging. Infection is milder when it is over 60°F during that time.
One attack of this disease does not cause serious harm, but repeated each year, it weakens trees to the point where they become victims of borers or winter injury. Large established trees can handle the infection on their own, but it should be treated in young, small trees. Collect and discard all fallen leaves, twigs, and other tree debris from under and around the tree to prevent spread of the fungal spores. Prune off any visibly infected twig or branch. Spray healthy foliage with a garden sulfur fungicide labeled for this use and use it according to label instructions. It will likely specify three sprays - once when the leaves begin to appear, again when they are fully unfurled, and finally 2 weeks after that. Hire a certified arborist to treat your tree with a systemic fungicide in early fall if it is large enough that you need to use a ladder to reach the foliage. Fertilize and water young trees to maintain their vigor.
Leaves Turn Pale, Mottled, Drop Early
Lacebug - Adult lacebugs are small squarish white bugs, about 1/8 inch long, with delicate, lacelike wings. They spend the winter sheltered in bark crevices and emerge in the spring to lay eggs on leaf undersides. New young bugs feed on the sycamore leaves, sucking juices from plant cells and causing the leaves to turn pale, then drop to the ground. Lacebugs are a persistent problem, since they launch several generations over a single growing season. For information about options go to Controlling Lacebugs
Trunks, Limbs Scared, Weakened, Twig Drop
Borers - Caterpillars of certain moths bore into trunks and branches of sycamores, weakening them and making them vulnerable to other pests and diseases. These worms may be grayish-white, pinkish or brownish-green. As they burrow into the wood of the tree, they make telltale holes in the bark. Their work scars small branches, weakening them and causing end twigs to die and drop off. The best defense against borers is a good offense. Avoid injury to healthy trees and maintain their vigor by feeding and watering properly. Prune away any branches that become seriously infested with borers before they break off and cause damage. Heavily infested trees should be cut down for the same reason. For more information see the file on Controlling Borers
Fewer, Smaller Leaves, Blue/Black Stains On Bark
Cankerstain - This fungal disease is a major problem of London planetrees, cousins of American sycamores which are only mildly susceptible to it, if at all. The fungus enters trees through bark injuries caused by saws, ropes, lawnmowers, pruners or something similar. It causes cankers, or swollen sores, to form on trunks and major limbs of trees. The exposed bark becomes stained with bluish or blackish streaks and tissue around the canker swells to form a callus, then dies quickly. The staining penetrates inward to the healthy wood tissue and generates brown, raylike streaks that spread throughout it. Meanwhile tree foliage becomes ever thinner and smaller. Affected trees die within a year or two.
Remove and destroy affected trees as soon as this fungal disease is diagnosed. Disinfect all tools and equipment used on the tree in a solution of hot water and household bleach or disinfectant spray to avoid spreading the fungus. Avoid injuring healthy trees. Keep them vigorous and healthy by proper feeding, watering and mulching.
Dog Urine - Along streets and occasionally in yards, sycamores are plagued with repeated exposure to dog urine on the lower two feet of their trunks. This causes cankers, or sores, that promote rot in tree tissues. Trees whose trunk diameters measure 6 inches or less can be killed. Shielding trunks of trees frequently visited by dogs with metal collars provides some protection against the cankers, but the urine will run down the shield and still soak into the soil and damage tree roots. Commercial animal repellent sprays are temporarily effective, but they usually wear off in the rain. If possible, establish a barrier such as a low fence several feet out from the sycamore trunk to discourage pet visits.