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Control of Phytophthora nicotianae with Mefenoxam, Fresh Brassica Tissues, and Brassica Pellets

Sensitivity to mefenoxam, fresh Brassicaceae tissues, and Brassica pellets was evaluated in several isolates of Phytophthora nicotianae recovered from pepper and tomato plants. The isolates of P. nicotianae studied were classified as sensitive to mefenoxam, showing great variability among isolates in the 50 and 90% effective concentrations (EC₅₀ and EC₉₀, respectively). Sensitivity differentiated isolates from the two hosts of origin, being isolates from tomato plants more resistant to fungicide than those from pepper plants. This differentiation also occurred in the case of fresh Brassicaceae tissues assay. The most effective biofumigant in inhibiting mycelial growth of P. nicotianae isolates was Brassica nigra. The effectiveness of B. carinata, Sinapis alba, and B. oleracea varied depending on the dose. Isolates differed in susceptibility to compounds released by the Brassica pellets and then in the EC₅₀ and EC₉₀. No significant difference was found between the isolates depending on the host of origin. Greenhouse tests demonstrated the effectiveness of treatments with mefenoxam and with Brassica pellets to control P. nicotianae in pepper plants. Mefenoxam application could be a solution to the disease caused by P. nicotianae in tomato and pepper crops in this region but its use could increase resistance in populations. Biofumigation is a promising technique which can be further developed to form part of integrated pest management strategies.