Avoid planting legume cover crops immediately before cole crops, or disk legume cover crops four weeks before transplanting or seeding cole crops, so there is time for the cover crop to partially decay.
Excess nitrogen also makes plants tender and susceptible. 3 High soil nitrogen levels enable Rhizoctonia to attack plant stems quickly. When legume crops, such as clovers, vetches, and beans, are disked into soil, the green residue increases the amount and activity of Rhizoctonia in soil by providing a food base for the fungus. Susceptible crops grown in heavy soils with loam and clay tend to have more wirestem than crops grown in sandy soil. This is because the pathogen is most active in warm, moist soil. In the southeastern United States, wirestem is more common and severe in the fall than in the spring. All cruciferous vegetables become less susceptible as their stems thicken with age. Other cruciferous vegetables, such as mustard, turnip, and rutabaga, belong to different Brassica species and are less susceptible than B. 1 These crops include the leafy greens collard and kale and heading cole crops like cabbage, broccoli, and cauliflower. The Host CropĪll cole crop vegetables in the species Brassica oleracea are all susceptible to wirestem. Rotation with non-cole crops for three or more years can reduce wirestem outbreaks when R. It is usually found on farms that grow cole crops repeatedly in the same fields, as this type of R. 1 Because AG 4 attacks a wide variety of vegetables and is adapted to survive in soil, crop rotation often will not control wirestem.Īnother type of R. solani that attacks cole crops is type AG 4. In the southeastern United States, the most prevalent and damaging type of R. This pathogen also causes pre-emergence damping-off of cole crops and bottom rot of cabbage. The soilborne fungus that causes wirestem is Rhizoctonia solani.
Stand loss in cabbage caused by severe wirestem. Because of stand loss and stunted plants, wirestem reduces the number and weight of marketable-sized heads of cabbage and broccoli or collard plants per acre (figure 2).įigure 2. Just as important, surviving plants may be stunted permanently and never produce a harvestable yield. Wirestem can occur on greenhouse-grown transplants if potting mix becomes contaminated or is mixed with infested native soil. Moist soil may stick to the lesions, held there by the fungal pathogen. Secondary aboveground symptoms associated with lesions that girdle the stem include wilting, stunting, and a blue color to the youngest leaves (figure 1). When wirestem is severe, the entire outer layer of the taproot rots away, leaving only the tough water-conducting tube in the center of the root (figure 1). The primary symptom is dark lesions of varying depth and length on the hypocotyl (seedling stem) at or just above the soil line. Wirestem is a disease of young vegetable brassica (cole crop) plants that affects both direct-seeded and transplanted crops.
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