Plant Pathology Infobytes

September 10, 1998
Start Disease Control Early for Clean Greens

Mississippians are awful picky about the quality of their turnip and mustard greens. 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.

Leaf blight control is important because during times favorable for leaf infection -- several days of rainfall or heavy dews--fungus diseases can develop and quickly blight an entire planting unless a preventive program of disease management is followed.

The most common disease which affects mustards and turnips is white spot (sometimes referred to as "pale 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 1/8 inch in diameter), but rapidly increase in size and number. 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. The following control measures will help minimize disease development in your crop:

* In the next crop, it will pay to rotate to a production area where leafy greens, or related crops haven't been grown within the past 2 to 3 years. This helps because most of the fungi which cause blight problems are carried over in the soil from season-to-season. So it's best to wait about 3 years before a repeat planting of leafy greens in such areas.

* If diseases were widespread in your past leafy green planting, don't use seed collected from such crops for the next crop, since they're likely to be contaminated with the white spot fungus. Fresh seed are always a good investment. Also, make sure you use fungicide-treated seed. If your seed are not treated (denoted by a red or green dye on seed coats), treat your own by placing about ½ cup in an envelope or zip-lock container. Add ½ teaspoonful of captan or thiram wettable powder directly to the container; seal and shake gently until the seed are evenly coated with fungicide. Treated seed should be planted promptly.

* Following stand establishment, a fungicide application program will be needed to protect greens from white spot and other fungus diseases. Fungicides will protect greens from diseases provided spray applications are made on a preventive basis. For best results, start a spray program within 2 to 3 weeks after seedlings have emerged and continue through the season.


Written by the late Dr. Frank Killebrew

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