The spores are splashed or blown onto green leaves where they germinate in the presence of water or dew droplets and infect the leaf. Leaf scorch occurs on younger and older leaves. In overgrown, frequently irrigationd beds, the spots become so numerous that the leaves dry and appear scorched. This reduces the photosynthetic capacity of the plant which in turn limits sugar storage in the roots along with its ability to survive winter. After several years, beds become thinned due to weakened winter-injured plants, and yields and quality decline.
Control involves both cultural and chemical practices.
When starting a new bed, plant varieties resistant to leaf spot into a location with well-drained soil. Space plants to avoid crowding and mulch between the rows. Remove dead leaf debris in early spring. It may be necessary to supplement these cultural practices with fungicide sprays using one of the products listed in Table I . Time the first application to protect the leaves from initial infection, and then repeat with cover sprays to maintain a healthy foliage during the season.