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. About one-half cup of seeds can be treated by placing them in a envelope or ziplock type container. Add one-fourth to one-half teaspoonful of captan or thiram directly to the container. Seal and shake gently until the seeds are evenly coated with fungicide. Treated seeds should be planted promptly.

* 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. Benlate 50 Wettable Powder is approved for white spot control on turnips. Apply at 14-day intervals, not to exceed three applica- tions. Dilute at the rate of 1/2 tablespoonful per gallon of water. Kocide DF or WP is also effective for white spot control. Kocide is a copper based fungicide, available in one to two pound containers at many farm and garden supply dealers, and may be applied to mustard, turnips, and other greens, on a 7- to 10-day schedule. Dilute at the rate of 1/2 to 1 tablespoonful per gallon of water.

Other fungicides approved for use on leafy greens may also be available at your local garden supply dealer. Note: When applying Benlate or Kocide, observe the following waiting periods (days from last application until harvest): Benlate 50 Wettable Powder - 14 days and Kocide DF or WP - 0 days.


Written by the late Dr. Frank Killebrew

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