Spotted leaves that fall in late spring or early summer point first to anthracnose, a fungal disease that causes leaf spots, leaf drop, and twig dieback on sycamores after cool, wet spring weather. Pale, speckled leaves point instead to sycamore lace bugs, and a white powdery coating to powdery mildew.

Why do sycamore leaves spot and drop after a wet spring?

Because the anthracnose fungus thrives in cool, wet, humid weather. Rain and wind carry it onto new leaves as they open, and it survives the winter on fallen leaves and in lesions on twigs, so a wet spring after an infected year often brings it back.

How can anthracnose be told apart from other sycamore problems?

By the type of damage on the leaves:

• Light brown dead patches along the veins, falling leaves, and dead twig tips after a cool, wet spring: anthracnose
• Fine pale stippling and discolored leaves: sycamore lace bugs
• A white powdery coating: powdery mildew
• Browned edges and early leaf drop during hot, dry weather: drought stress

How is sycamore anthracnose managed?

With cleanup first and fungicide where infection is heavy. Fallen leaves are raked and destroyed, and dead twigs are pruned out in dry weather with tools disinfected in 1 part bleach to 4 parts water between cuts. At the first sign of disease, Liquid Copper Fungicide Spray, which lists anthracnose on sycamores, is applied with a hose end or pressurized hand sprayer and repeated every 7 to 14 days as needed.

Frequently Asked Questions

How are lace bugs controlled on a sycamore?

With insecticidal soap or a pyrethroid spray. Where lace bugs leave the leaves stippled, Bug Buster II Insect Spray, a synthetic pyrethroid, is mixed at 1 ounce per gallon of water, and TreeHelp's sycamore guide names it alongside insecticidal soap for lace bugs.

Is a fall spray worth doing?

It can be. Spraying the tree and the ground around it in fall reduces the spores that survive the winter.

Does powdery mildew on a sycamore need treating?

Usually only when it is heavy. The same copper fungicide is recommended for powdery mildew on sycamores.

Does a sycamore need spraying every year?

Not always. Yearly leaf cleanup and pruning of dead twigs reduce the fungus, and spraying is kept for trees hit hard season after season.