University of Massachusetts Amherst
UMass Extension Vegetable Program
Vegetable Program
Disease Management
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Diseases
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Cabbage Phoma Black Leg BLACKLEG OF BRASSICASThe Plant Diagnostic Clinic Revised December 2005 Blackleg caused by Phoma lingam attacks many brassica crops and can spread rapidly within a field. The disease has become less important in brassicaous crops because of successful disease management strategies in seed production. Plants can become infected at the seedling stage or at any stage in the field. Phoma lingam can survive for up to four years in seed and three years in infected crop debris. The pathogen infects seedlings, forms pycnidia, and produces abundant amounts of spores which exude from the pycnidia in long coils and are splashed to nearby plants to initiate new infections. The disease is favored by wet, rainy weather. Management:
Chemical recommendations:
potassium bicarbonate (Armicarb 100): 2.5 to 5.0 lb/100 gal (0 dh, REI 4h).Start application at the first sign of disease and continue at 7-14 day intervals while conditions remain favorable for disease development Prepared by M. Bess Dicklow, UMass Extension, 107 Fernald Hall, University of Massachusetts, Amherst, MA 01003-9320. Tel. 413-577-1827 Fax. 413-545-2115. mbdicklo@umext.umass.edu
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Symptoms of the pathogen start as slight lesions on stems at cotyledon scars which elongate, turn brown with a black to purplish border, and become sunken. The lesion extends up and down the stem, the stem becomes girdled and blackened, with many fruiting bodies (pycnidia) embedded in the tissue. Lesions may extend below the soil and attack roots. Diseased plants often wilt, lodge, and die. On root crops, symptoms occur in the form of cankers on the fleshy roots and a dry rot may appear in storage. 
