(05/19/26) BATON ROUGE, La. — Following recent heavy downpours, Louisiana has been experiencing cooler-than-usual nighttime temperatures — conditions that are highly conducive to Pythium diseases, which are harmful to vegetable crops.

Raj Singh, LSU AgCenter plant doctor and horticulture pathology extension specialist, said growers across the state have reported disease problems with their vegetables, especially those in low-lying areas of fields.

Pythium species thrive in wet soils and low temperatures, Singh said. Commonly known as water molds, Pythium species are soil-inhabiting, fungal-like microorganisms that are known to cause damping-off, root rot and cottony leak on a wide variety of vegetables as well as annual ornamental plants.

The diseases also may occur when seeds are planted too early in spring, are planted too deep or when old seeds are used, Singh said.

Seedlings affected by damping-off exhibit dark lesions on their stems at the soil line. The stems later rot, causing seedlings to fall over. As the disease develops, roots rot, and water and nutrient uptake is interrupted. In some cases, bark easily sloughs off on the lower stem where rotting occurred. Affected seedlings eventually die. In some cases, white, cottony mycelial growth can be observed growing profusely on fruiting vegetables.

Management of Pythium diseases requires an integrated approach, Singh said.

“Good cultural practices — including proper soil preparation, use of raised beds to provide adequate water drainage, proper planting depth and plant spacing and planting in well-fertile soils with proper soil pH — play a key role in growing healthy seedlings,” he said.

Avoid sowing seeds or transplanting seedlings into cool, wet soils, he added. Overwatering before or during the germination process may adversely affect seedling stands, too.

Use of fungicide-treated seeds or transplants also may be beneficial, Singh said. Common fungicides labeled for managing Pythium diseases in commercial field-grown vegetables include MetaStar 2E, Ridomil Gold 4 SL, Orondis Gold DC and Previcur Flex.

For more information on fungicide use, search for the Louisiana Plant Disease Management guide at www.LSUAgCenter.com.

Pepper seedlings showing damping-off symptoms on the stem near soil line caused by Pythium species. Photo by Raj Singh/LSU AgCenter

Rotting and sloughing of roots of a bell pepper plant caused by Pythium species. Photo by Stuart Gauthier/LSU AgCenter

A young watermelon fruit exhibiting white, cottony mycelial growth of Pythium species. Photo provided by Chuck Melsheimer