What diseases can affect leafy vegetables?
Listed below are several diseases that most frequently occur on leafy vegetables. Symptoms are described briefly. Colored pictures of disease symptoms can be seen in the publication "Identifying Diseases of Vegetables" available from the Penn State Publication Distribution Center, or from extension offices.
Lettuce White Mold (Drop) and Gray Mold
A wet rot appears at the base of the plant where outer leaves touch the soil. During wet weather, especially when plants are mature, rots progress into the head. Distinctive mold growth develops on the surface of affected tissue. Sclerotinia mold is white and Botrytis mold is gray and appears powdery. Soft rot bacteria can follow the molds and result in slimy rotted heads.
Control: Remove diseased plants (heads, dead leaves, and roots) as soon as symptoms appear. Do not plant lettuce in areas where similar disease has appeared in recent years on lettuce, cabbage, celery, tomatoes or cucurbits. Plant in well-drained soil.
Spinach Downy Mildew
A yellow spotting first appears on the top surface of leaves. If downy mildew is the cause, following wet cool weather, a violet to gray mold will appear on the underside of leaves, directly under the yellowish area observed on the top surface. Affected areas on leaves die.
Control: Where disease is a persistent problem, plant resistant varieties and rotate with other crops. Where necessary, consider trying labelled garden sprays that contain a fixed copper.
Spinach Mosaic (CMV)
This can be a problem in fall crops. First, young leaves on isolated plants become mottled; later, older leaves on these plants can turn yellowish, plants are stunted and in severe cases, plants may die. High temperatures promote rapid development of symptoms.
Control: Grow resistant varieties.
Clubroot of Turnip and Mustard Greens
The first sign that clubroot is present is a wilting of plants, especially where soil has been wettest. Pull a wilted plant to determine whether the wilting is caused by clubroot or insect grubs. Clubroot is characterized by distinct swellings on the tap and branch roots.
Control: Rotate all plants in the cabbage family (cabbage, cauliflower, broccoli, Brussels sprouts, raddish, collards, kale, etc.) with unrelated plants. Where clubroot is present, following several years without related plants, clubroot may be minimized by applying hydrated lime to the soil before planting (3 to 4 lb/100 square feet), mixing it thoroughly into the soil, and by providing good soil drainage.
Dr. Alan A. MacNab, Professor, Plant Pathology
Penn State College of Agricultural Sciences
211 Buckhout Lab, University Park, PA 16802
Loaded: June, 2003
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