Assessment of Efficacy of ametoctradin + dimethomorph (Orvego® 525 SC) in the Control of Watermelon Downy Mildew, Pseudoperonospora cubensis

Watermelon downy mildew caused by the fungus-like pathogen Pseudoperonospora cubensis (Berk. & M.A. Curtis) Rostovzev is one of the most important diseases of this crop in Iran. The aim of this study was assessment of efficacy of the fungicide ametoctradin + dimethomorph (Orvego® 525 SC) to control watermelon downy mildew in a completely randomized block design with four replications in Hormozgan and Mazandaran provinces. Treatments included Orvego® of three dosages 0.6, 0.7 and 0.8 ml L-1, Potassium phosphite (Phosphite®530 WSL) of dosage 3 ml L-1 as standard fungicide and a control treatment without fungicide application. The treatments were applied upon appearance of the first disease symptoms and repeated with 7- to 10-day intervals. Statistical data analysis was done using SAS software and comparision of means was carried out using protected least significant difference (PLSD). According to the results, Orvego of dosage 0.8 ml L-1 had the highest efficiency in the disease control (%89.85 in Hormozgan province and %80.05 in Mazandaran province); however, it did not significantly differ with Orvego of dosage 0.7 ml L-1 (%88.88 in Hormozgan province and %77.48 in Mazandaran province) and Potassium phosphite of dosage 3 ml L-1 (%87.72 in Hormozgan province and %75.60 in Mazandaran province). Since the severity of watermelon downy mildew under the influence of Orvego of two dosages 0.8 and 0.7 ml L-1 did not significantly differ, application of the least effective dosage of the fungicide for controlling of downy mildew in watermelon fields is recommended.