Important diseases: Late leaf spot of peanut, leaf spot on ligustrum, azalea, hydrangea, pansy
Cercospora is a very common fungus causing leaf spots on a wide variety of plants including vegetables, field and forage crops, and woody and herbaceous ornamentals. Leaf spot symptoms vary with host, but are sometimes referred to as "frogeye." On peanut, Cercospora leaf spot is characterized by brown to black circular spots on leaves often associated with a yellow halo around the necrotic spots. Spots enlarge, coalesce and cause defoliation.
On some plants such as ligustrum (privet), Cercospora causes numerous small, roughly circular, tan to brown leaf spots with reddish purple borders. On azalea, leaf spots are initially small and reddish, but they enlarge rapidly with the center of the spot turning an ash gray color. Small black specks may be observed within the spot center. These specks are masses of spores (conidia) borne on conidiophores.
Conidiophores are darkly pigmented, sparingly branched, and septate (having cross walls). Conidiophores are produced in clusters from the plant stomata within infected tissue.
Conidia vary greatly in size depending upon Cercospora species. In general, conidia are long, slender, colorless (hyaline), straight to slightly curved, and multicellular having 5-10+ septations (cross walls) per spore. One end may be slightly more narrow than the other.