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.