How to Manage Pests
UC Pest Management Guidelines
The most serious symptoms occur on stems near the soil line where elongated, sunken, brown lesions form. These lesions may girdle the stem, resulting in stunting, wilting, and general poor growth of the plant. If the lesions enlarge, the stem may break, causing the plant to fall over. Lesions usually contain minute, spherical, dark structures that are the fruiting bodies of the pathogen. If conditions are right, pink masses of spores exude from these structures. If seedlings are infected early, they may die. Less important are the leafspots that may develop on foliage. Leafspots are circular, light tan, and contain the dark, spherical fruiting bodies of the pathogen. The disease damages the water-conducting tissue, and blackened streaks of xylem can be seen by cutting open the stem.
Of particular importance is the ability of this pathogen to be carried in and on seed. This is how the fungus is introduced into greenhouse and field plantings. The pathogen can live in crop debris if such material is not fully decomposed. Cool, moist conditions enhance disease development. Spores are spread with splashing water. A second spore type may occur that can be blown long distances on wind currents.
Black leg can be managed by using disease-indexed seed, by cultural practices, and with foliar sprays. Remove cruciferous weeds and volunteer plants that may harbor the pathogen. Plow under debris in diseased fields to allow for more rapid and thorough decomposition. Practice crop rotation; rotate infested fields out of cruciferous crops for 1 or 2 years.
UC IPM Pest Management Guidelines: Cole Crops