Efficacy of Heritage, RootShield WP, and Subdue Maxx for the Management of Pythium Root Rot in Lettuce Greenhouse Transplants in California, 2025

Pythium root rot, caused by Globisporangium irregulare (previously Pythium irregulare ), is a worldwide pathogen in a variety of vegetable crops and ornamentals causing root rot, stunting, wilting, and damping-off. Other closely related Pythium species have been associated with symptomatic lettuce in fields and vegetable transplant nurseries on the California Central Coast (Smith & Dundore-Arias, 2020). This report evaluates the efficacy of a standard synthetic (Subdue Maxx), a biological (RootShield WP), and an unregistered synthetic fungicide (Heritage) for the management of Pythium root rot in greenhouse lettuce ( Lactuca sativa ‘Ice Queen’) seedlings. Results from these trials aim to improve management of this disease in greenhouse and nursery production.