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Bean blight

Xanthomonas axonopodis pv. Phaseoli
  • Use seed that is certified/free from bacterial infection
  • Use tolerant or resistant varieties if available
  • For smallholders who save their own seed:
    • Select plants for seed without marks on the leaves or pods (disease symptoms)
    • If most plants show symptoms, do not use them as a source of seed
    • Sterilize the seed. Use heat treatment (20 minutes at 52°C) and a certified antibacterial agent (try this on just a few seeds first)
  • Remove weeds, volunteer beans and other legume crops from the field before planting and as they appear. This eliminates sources of the bacterium and improves aeration
  • Do not plant new crops next to infested crops
  • Use maize as an intercrop; it reduces spread of the bacterium between bean plants by creating a physical barrier
  • Allow plants to dry before allowing workers or machinery to enter the field to prevent the spread of the bacterium
  • Avoid over-irrigation
  • Rotate crops of beans every 2-3 years with non-susceptible crops, e.g. maize
  • Relevant crops: common bean (snap or French bean), Phaseolus spp., including Phaseolus vulgaris,and Vigna beans
  • Monitor for symptoms from seedlings to harvest, especially during favourable conditions (wet weather and temperatures between 28-32°C):
    • Seedlings: spots which then produce spores to infect other leaves
    • Leaves: small angular spots that look water-soaked, expanding as large brown dead areas. Spots may continue to expand and the leaves appear burnt and become torn
    • Stems: dark streaks becoming lighter as they age
    • Pods: spots are water-soaked at first, becoming red-brown and sunken, mostly circular. A yellow liquid containing bacteria seeps out of the spots when plants are wet and humidity is high. In severe cases, the pods shrivel and die
  • After harvest, collect and burn or plough back the diseased crop. The bacterium probably survives only a few months in soil in the absent of a host

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