Pathogen and symptoms
Wirestem is a disease of cole crops (e.g., broccoli, cauliflower, and cabbage) caused by the soilborne fungus Rhizoctonia solani. This summer, cole growers from the state’s northern region reported that their crops were affected by poorly developed root systems. Upon examination, the plants showed brown stems (figure 1) and narrow roots with constrictions about one inch below the soil surface. Above ground, the plants exhibited yellowing symptoms (figure 2) and occasional death. Samples from these fields were sent to the PPDL and confirmed positive for Rhizoctonia. Additional symptoms of this disease in the field include wilting, purple leaves, and stunted growth. When the soil is heavily infected with Rhizoctonia, dark brown and oval lesions can develop on leaves in direct contact with the soil.
Figure 1. Wirestem symptoms on the lower stem of a brassica plant. Notice the brown coloration on the lower stem (Photo by Jeff Burbrink).
Figure 2. Yellowing and purple symptoms on a brassica plant. These symptoms are typically caused by Rhizoctonia infection (Photo by Jeff Burbrink).
Management
Rhizoctonia can survive in the soil for long periods using structures called sclerotia, making disease management complex. However, we recommend several measures that growers should consider before and during planting:
- Site selection: Avoid planting in fields with poor water filtration. Wet and warm soils, especially during summer, create a suitable environment for this disease.
- Crop rotation: Implement rotation with non-cole crops to reduce disease incidence.
- Transplant quality: Use certified, fungicide-treated seeds and inspect seedlings to ensure they are disease-free before transplanting.
- Scouting and removal: Regularly scout fields and greenhouses, removing any infected plants or seedling trays completely to prevent pathogen buildup. Early disease detection is crucial for effective curative treatments.
If you suspect your plants are infected with this or any other disease, contact your local extension educator or Purdue vegetable pathologist, Cesar Escalante (escalac@purdue.edu). You can also send samples to Cesar Escalante or directly to the PPDL. Accurate disease diagnosis ensures appropriate action to reduce disease progression and prevent yield loss.
Conventional fungicide applications can be made with Blocker 4F® (PCNB) and Endura® (WG). Organic pesticide products based on Streptomyces, Trichoderma, Bacillus, and other compounds are also used to manage wirestem in cole crops; however, growers should ensure the product is labeled for the specific crop grown.
Additional resources
Egel et al. 2024. Cole crops and brassica leafy greens – Diseases. Phillips et al. (eds), Midwest Vegetable Guide. https://mwveguide.org/guide.
Purdue Plant and Pest Diagnostic Lab. Submit a sample. https://ag.purdue.edu/department/btny/ppdl/submit-samples/submit-sample.html.
Seaman. (ed). 2016. Production guide for organic cole crops. New York State Integrated Pest Management Program. http://hdl.handle.net/1813/42893.