Seed rot and damping-off
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Cucurbit seeds need warm soils to germinate and develop properly (65F at 2" depth). Seeds that are planted in cold, wet soils are at risk of seed rot and damping off. These diseases are caused by several different fungi that live in the soil including Rhizoctonia, Pythium and Fusarium. Damping off fungi infect and rot both seeds and young seedlings. Infected seeds may not emerge from the soil. Seedlings may emerge with soft brown water soaked areas on the cotyledons (seed leaves). Stems may be thin, wire-like and unable to support even the small seedling. Fine cobweb like fungal mycelia may be visible growing on wet potting media and infected seedlings. Infected plants are unlikely to grow into a mature plant.
Seed rot and damping off can be avoided by following several cultural practices. Do not plant cucurbit seeds outdoors until soils have completely warmed to 65F at a 2" depth. Keep beds moist but not water logged. In areas of Minnesota where the weather will not provide these conditions, pumpkin, squash and some melon seeds can be started indoors. Seed plants in pots that are at least 2 inches wide and deep. Transplant seedlings once they have 2-3 true leaves and soil temperatures have reached 65F. Take extra care not to disturb the plants root system or damage the plant when transplanting cucurbit seedlings. Some seed companies provide 'treated seed' which is coated with a layer of fungicide that will help to prevent seed rot.