Tar spot

Natural History
Tar spot on maple
Photo credit: Steven Katovich, USDA Forest Service, Bugwood.org

Tar spot is caused by species of fungi in the genus Rhytisma. Tar spot gets its name from the characteristic black, tar-like spots that develop on infected leaves. The disease can occur on numerous tree hosts, but is most common on willow, maple and holly. In Florida, the disease occurs in summer as leaves are infected by spores released from infected leaves from the previous year. No control is necessary as the disease, although striking, is only cosmetic and does not affect health of trees.


 

Identifying Characteristics

Identifying the injury: Shiny black, roughly circular spots with raised surfaces on affected leaves. Later in the season, "spots" may fall out of leaves leaving holes.
Identifying the pathogen: The black spots are actually the fungal reproductive structures (stroma) and contain tiny, microscopic spores.
Susceptible trees: Mostly maples, willows and hollies in Florida.

 

Images

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