Leaf blight of fennel
The disease primarily affects older foliage. Affected leaf tips and stems turn brown to black in color and dry up. Examination of the stems and leaves show tiny, discrete, dark brown to black fungal patches. Early patches are less than one-sixteenth inch wide, and can be oval, circular or irregular in shape.
If the disease is severe, the patches multiply and grow together resulting in an overall dark appearance and death of the foliage. If sufficient humidity and moisture occurs, a white crusty growth forms on top of the patches. The white crust is made up of clusters of the pathogen’s spores. Cercosporidium blight does not kill fennel plants, but can impact growth and result in a poor quality product.