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Tar spot attacks slowly, creating management challenges

A plant pathologist says tar spot is unlike many crop diseases.  Dr. Damon Smith with the University of Wisconsin tells Brownfield they’re learning more about the biology of the tar spot fungus, and finding it attacks plants slower, and then ramps up. “That tar spot fungus is really sneaky. It actually gets into the plant and can colonize that plant before the plant sort of recognizes that it’s infected, and then it sort of consumes the plant almost from inside out, which is really weird. It sounds like a horror film.”

Smith says fungicides can help reduce the infection process and slow the fungus down, but in the end, the corn cannot overcome the disease. “The leaf area no longer can produce carbohydrates for the plant, and so the plant is still trying to fill out the ear so then it will scavenge the stalks as well, so we see fast dry down, we see standability issues and all of those things were tar spot is especially heavy.”

Smith says gray leaf spot and northern corn leaf blight affect corn plants in the same way, but much faster than tar spot, and a fungicide application helps the plants finish better.

Smith’s team has developed the Tar Spotter smart phone app for predicting when tar spot is likely to develop.  It’s free and available on Apple and Android platforms.