The fungus is among us!

The sunshine today afforded me a wonderful opportunity to gallivant and admire the fall foliage, something I have been unable to accomplish between work and rainy days. As I moseyed along, I noticed a strange leaf on the ground, so I was compelled to pick it up and admire it properly. It had the “black spot.” I chuckled to myself for a moment in reverie of a scene from “Pirates of the Caribbean” where Captain Jack Sparrow was marked with the ‘black spot.’ When I came back from the little world I had floated off to, I began to ponder what the little spot was. I had decided it must be some kind of fungus, and proceeded to tote my little leaf along with me for the rest of the day.

Upon returning to my room, curiosity got the best of me as I searched to answer my conundrum. I discovered this black spot of mine is a fungus, as I had suspected, called “tar spot.”

An indication of early stages of tar spot includes the appearance of small yellow spots on leaves. The yellow spots grow in size and intensify in color, black spots finally appearing in the center. The black spots grow and form large dark circles on the leaves.

The fungus gets its name from these black splotches, which resemble drops of black tar. Tar spot, or Rhytisma acerinum, is a fungus that affects maple trees (among others), usually causing early leaf drop. Tar spot is a kind of fungi called an endophyte ("endo-" meaning "within", "-phyte" meaning "plant"). Since the area of the tree affected is the leaves, which are deciduous, tar spot does not cause long-term damage to its hosts.

Moist, cool conditions, around 60 degrees F, compliment the fungus and cause rapid spread of tar spot. Tar spot typically infects trees in the spring, when tiny, needle-like spores are released into the atmosphere, carried by the wind. The spores, landing on vulnerable leaves, infect the tree and begin a new cycle of tar spot.

Since tar spot does not cause long-term damage to trees, many choose not to use fungicide against it. Fungicides are often ineffective, expensive, and are generally harmful to the environment. One environmentally-friendly way to manage the spread of tar spot is to efficiently rake the leaves that have fallen from infected trees, and those of trees in the surrounding area. Mulching the leaves has proven to be effective, but covering and containing the leaves will also help reduce the infected area.