Plant Pathology Infobytes
August 27, 1996
Keep Your Greens Blight-Free
Mustard and turnips are fall favorites in many Southern gardens. 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.
- If you haven't already planted mustard and turnips, it will pay to rotate to an area of your garden where greens haven't been grown in several years. This is true because the fungi responsible for white spot are carried over from season-to-season in the soil. It's best to wait about three years before again planting turnips or mustard in such areas.
- Mustard or turnips seeds collected from a previous crop where diseases were prevalent are likely contaminated with white spot fungi. To reduce the chances for disease from using carryover seed, it's best to treat seeds with a fungicide prior to planting.
- While these practices will help, you may need to apply fungicides as part of your green disease control program. Fungicides will protect greens from infection, provided spray applications are made on a preventive basis. Don't wait until disease symptoms are widespread on your greens before applying a fungicide. For best results, start a fungicide application program within two to three weeks after plants have emerged and continue through the season.
Infobytes newsletter was written by the late Dr. Frank Killebrew, Extension Specialist.