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Pythium root rot (Pythium spp.) causes brown, rotting roots. Stem constrictions may occur at the soil line, sometimes with a lesion extending upward. Like other root rot diseases, plants may be stunted, exhibit nutrient deficiency symptoms, and suffer reduced yields. Pythium species are water mold pathogens with very wide host ranges.

Pythium root rot (left) and healthy (right) watermelon transplant roots.

(Photo: Gerald Holmes, California Polytechnic

Management:

• Increase soil drainage and avoid overwatering.
• Avoid introduction of natural soil into hydroponic systems.
• Use approved soil- or media-applied fungicides labeled for Pythium spp.

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