Although gardeners are generally successful in producing a quality crop, it pays to keep an eye out for fungus diseases which can quickly blight an entire planting. The most common disease which affects mustard and turnips is white spot. Symptoms of white spot include circular, gray to brown or almost paper white spots, with slightly darkened margins. At first these spots are small, about one-eighth inch in diameter. The spots rapidly increase in size and number, and over a period of 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 season, are blown by wind or splashed by rain onto plant parts. Numerous infections originate from these spores and occur during rainy periods in early autumn when temperatures are in the 55 to 65 degree F range. The key to keeping greens blight-free is to start a control program before white spot becomes widely distributed. The following measures will help to minimize disease development in your greens.