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Rhizoctonia damping off in watermelon transplants

Lately, UGA Plant Disease Clinic at Tifton received number of watermelon transplants with typical Rhizoctonia symptoms.  Rhizoctonia infection may cause a sunken, necrotic lesion near the soil line in seedlings. The lesion girdles the stem, and the seedling collapses and dies quickly.

Cultural control

  • In the greenhouse or seedbed, use only new, pasteurized soil mix. Heat treat any other soil; for example, most pathogens die if soil is heated to 158°F (70°C) for 30 min. with aerated steam.
  • Use new flats or pots for planting, or thoroughly wash and disinfect old containers before using.
  • If damping-off starts, stop watering for a while. Allow soil around the plants to dry somewhat. If the seedlings are in flats or in cold frames, give them as much air and light as possible.
  • Use transplants beyond the first-true-leaf stage for field or garden plantings.

For chemical control, please contact your county extension agent for UGA recommendation.