Fusarium Dry Rot

Causal Organism: Fusarium sambucinum, F. solani var. coeruleum and F. avenaceum

Crops Affected: Potatoes

Disease Cycle:

• Inoculum is found in contaminated soil (as spores or pieces of mycelium) or in infected tubers
  • Infected tubers are considered to be the main source
• A wound or entry point is required for the infection of tubers
• After infection, the disease develops within infected tubers throughout the storage period
• The disease does not spread between tubers in storage

Symptoms:

• Slightly darkened, shallow lesions become apparent within a month of infection
• Infected tissues become sunken and somewhat wrinkled, with concentric rings of discoloured tissue radiating from the initial point of infection
• Rotted tissues are dry, with cavities lined with mycelium and spores
  • Early stages of infection may be damp/wet, with tissues discoloured and water-soaked
  • Gradually, the rotted areas spread out to create the characteristic dry cavities
• Tubers may become completely shrivelled as rot advances and tissues dry out
• The extent of infection and internal tissue rotting may not be evident from the surface of the tuber
  • The degree of tissue rotting may only be exposed at cutting

Management:

• Avoid wounding tubers at any stage of production
• Adjust and calibrate all equipment to minimize wounding
  • This includes planting, harvest, and post-harvest handling equipment
• Maintain good sanitation during the pre-planting period (i.e. seed preparation, planting, etc.) and post-harvest (grading, sizing, etc.) activities
• Ensure that there is adequate skin set prior to harvest by top killing plants at least 2 weeks before harvesting
• Ensure that there is an adequate curing period to promote wound healing prior to long-term storage
• Fungicide applications at bin loading are relatively ineffective, as contact between infected areas and control products is difficult to achieve
  • Surface-applied fungicides may help to protect wounded tubers initially until wounding healing can occur
  • Fungicide resistance is also very prevalent in Western Canada
• Maintaining a low storage temperature can help to slow the development of this disease in storage (adjust according to type of potatoes being grown)