VERMONT -- It's been a lackluster year for Vermont's leaf peepers, and the problem wasn't helped any by a particularly nasty outbreak of "giant tar spot." This new and unsightly leaf blight, which only afflicts Norway maples, began showing up this summer throughout Chittenden County and other sections of Vermont, and has hit Burlington's Hill Section especially hard. But according to City Arborist Warren Spinner, the problem is nothing for residents to get too concerned about, since it usually doesn't threaten the health of an infected tree.
Giant tar spot is caused by a fungus that typically occurs after an unusually wet spring. The fungal spores lie dormant in leaf litter from the year before and spread to the new leaves when they bloom in May and June. By mid-summer, the blight appears on maple leaves and samaras. It resembles large, raised droplets of tar -- hence the name. This particular tar-spot variety, which is new to Vermont, doesn't seem to affect sugar, silver or red maples.
"Is this going to set the tree back or kill the tree? Normally, it does not," Spinner adds. Though giant tar spot can prematurely defoliate a tree, Spinner says that by the time the spots appear, the tree has already completed much of its photosynthesis for the season.
While there's no easy way of getting rid of tar spot, Spinner recommends raking up leaves and getting them off the lawn before next spring. Residents shouldn't worry that adding infected leaves to compost will further the blight, he notes, since the spores are already ubiquitous throughout the county.
Will the black spots mar the landscape next year as well? It all depends on the weather, Spinner says. If next spring is unusually dry, the spots may not appear at all.