Evaluation of some current fungicides against downy mildew caused by Pseudoperonospora cubensis Rostovzev. on greenhouse cucumber

Downy mildew caused by Pseudoperonosprora cubensis is the most important foliar disease of greenhouse cultivated cucumber which causes significant economic damages in Iran annually. The effect of five fungicides including Cyazofamid (Ranman® SC 34.5), potassium phosphate (Fosphite® WSL 53%), fluopicolide (5.53%w/w) (55.3%w/w) propamocarb hydrochloride (Infinito® SC 687.5) and famoxadone cymoxanil (Equation pro® WDG 52.5%) on the control of the disease was assessed in a greenhouse in Arbatan (Marand, East Azerbaijan, Iran) with precedent infection. The experiment was performed in a completely randomized design with 11 treatments and four replications during 2014. Treatments included Ranman at the rates of 0.2, 0.3 and 0.4 ml/l, Fosphite at the rates of 2, 3 and 4 ml/l, Infinito at the rates of 1.25, 1.5 and 2 ml/l, Equation pro at the rates of 0.3 g/l and control without spraying. Spraying was carried out immediately after the appearance of disease symptoms and was repeated for 3 times at intervals of 10 days. Data on disease incidence was recorded one week after the third spraying of fungicides. For this purpose 100 leaves were collected from 10 plants randomly from each plot and disease severity was assessed by measurement of diseased spots on the surface of leaves and sporangium formation density. Collected data were analyzed by SPSS software and means comparison were done by Duncan's multiple range tests. Results indicate that fungicide application caused significant decrease in the disease severity compared with the control treatment. Minimum disease severity occurred in Ranman 0.4 ml/l, Fosphite 4 ml/l and Infinito 2 ml/l with the disease severity of 3.3, 7.53 and 8.69% respectively compared to the control treatment 79%. These fungicides can therefore be applied as alternatives to other chemicals in the control of cucumber downy mildew.