Evaluation of conventional fungicides and disease resistance inducers for the control of downy mildew (Pseudoperonospora cubensis) on melon (Cucumis melo)

Abstract

Cucurbit downy mildew, caused by the oomycete Pseudoperonospora cubensis (Berck & Curtis) Rostovtsev, is one of the most important diseases of melons in Costa Rica. The control of downy mildew by the application of conventional fungicides in combination with resistance inducers was inves-tigated on melon (Cucumis melo L.) cv. ‘Ruide ra’. Two systemic fungicides, mefenoxam (1.96 kg a.i.ha^-1) and dimethomorph (0.45 kg a.i.ha^-1), and a sequence of the protectant fungicides chlorothalonil/mancozeb (2.01/1.20 kg a.i.ha^-1), were applied, by themselves or in combination with application of each of 3 resistance inducers, phosphite (1.01 kg a.i.ha^-1), menadione sodium bisulphite (MSB, 0.14 kg a.i.ha^-1) and acibenzo-lar-S methyl (ASM, 0.02 kg a.i.ha^-1). Controls with no fungicides or no inducers were included in the experiment. Significant differences ( p < 0.05) in area under the disease progress curve (AUDPC) were observed among fungicides. The lowest values of AUDPC were obtained with the chlorothalonil/mancozeb sequence, and with dimethomorph. Mefenoxam was not effective. The combination with phosphite improved the efficacy of all the conventional fungicides. No effect in disease con-trol was observed with the application of MSB or ASM, either alone or combined with conventional fungicides. The treatments chlorothalonil/manco-zeb and dimethomorph were less expensive than other treatments with lower efficacy.