One of the best ways to insure successful production of a quality crop is to start early in the season with a program to keep leaf blight diseases under control. Symptoms of white spot include circular, gray to brown or almost paper white spots, with slightly darkened margins. Within a week or so, the entire leaf may become blighted.
Leaves turn yellow and eventually die.
White spot is more of a problem when free moisture from rain or heavy dew creates conditions favorable for plant infection. Fungus spores produced on residue from earlier crops, some weed species such as wild mustard, and leaves infected within the same season, are blown by wind or splashed by rain onto plant parts. Numerous infections originate from these spores and occur during wet periods in the fall or spring when temperatures are in the 55 to 65 degree F range. The key to production of blight-free greens is initiation of a control program before white spot and other fungus diseases become established. So it's best to wait about 3 years before a repeat planting of leafy greens in such areas.