Cercospora blight is the most important disease of asparagus in Oklahoma. It can be particularly severe in the eastern half of Oklahoma where rainfall and humidity levels favor infection. The fungus over-winters on fern residues left on the soil, and spores produced on this debris infect ferns after harvest when conditions are favorable for infection. Spores of the fungus are produced on the lesions and are dispersed by wind and rain. Development of the disease depends on rainfall and humidity levels during June to August.
Browning progresses upward from the lower ferns as conditions favor spread of the disease.
Entire ferns may be blighted by late July in a wet year. The disease results in reduced photosynthesis of affected ferns. Yield loss the following spring is a result of reduced crown vigor caused by the early defoliation. Repeated yearly defoliation by Cercospora blight weakens crowns and reduces stand productivity and longevity. First-year asparagus is rarely affected by Cercospora blight.