Fungus set to blight fall’s blaze of color

All across the North Fork, maple tree leaves are turning brown and spotted and falling to the ground, snuffing out all hope of a blazing display of October color.


The trees aren’t dead or dying, but the leaves likely are suffering from a fungus infection known as tar spot. The name describes how the fungus first appears as dark tar droplets. Norway maples, which are quite common locally, are particularly susceptible.


Given the extremely wet conditions in late spring and early summer, the tar spot infection is far from surprising, said Tom Kowalsick, senior horticulture consultant for Cornell Cooperative Extension in Riverhead. And he wasn’t a bit taken aback to find the spots on the tree outside his Jamesport home.


“The majority of Norway maples that are getting brown leaves and dropping early have tar spot,” he said. Other more common fungi might also be present, he added.


Mr. Kowalsick said he cannot recall an infection as widespread as this year’s, but the condition is far worse in some upstate communities.


The fungus actually hits in the spring, but doesn’t appear until late summer. “This year the trees seemed to turn brown so quickly, that masked the spots on some leaves,” Mr. Kowalsick said.


In this case, diseased leaves do not a diseased tree make.


“Diseases or insects that affect leaves in late summer for the most part are not a serious threat because the leaf has already done what it had to do,” he said. Using photosynthesis, leaves convert carbon dioxide into sugars and oxygen. With that process finished, “dropping off a few weeks early won’t make much of a difference,” said Mr. Kowalsick.


The most noticeable difference will be the lack of bright fall colors.


There’s no point in spraying trees with fungicides since that’s a preventative measure and the infection took hold months ago.


“By the time all the symptoms appear it’s too late,” Mr. Kowalsick said.


The fungus survives by wintering over on fallen leaves and producing spores in the spring. The Cooperative Extension service says the most effective method to limit tar spot is to rake and remove the leaves. Mulching leaves will destroy many of the spores, but the mulch pile should be turned or covered before new leaves appear in the spring.