Factors affecting development of downy mildew of cucumber grown under plastic low tunnel and its management with fungicides

Downy mildew caused by Pseudoperonospora cubensis (Berk. and Curt.) Rostow has become a serious problem in successful cultivation of cucumber grown under low plastic tunnel in Punjab. Maximum disease severity (80.0%) was recorded at Khalehra in district Amritsar and minimum (12.5%) at Laddowal in district Ludhiana. Study on effect of sowing dates on development of cucumber downy mildew during 2008–09 and 2009–10 crop season revealed that mean disease severity of 22.93 and 38.61 per cent was recorded on cucumber cultivar Poinsett and Punjab Naveen, respectively when the crop was sown on 15^th December. The disease severity increased with delay in date of sowing and it was recorded as 35.65 and 53.16 per cent, respectively, on these cultivars when sown on 30^th January. Relative rate of disease progress r and AUDPC were also observed at these sowing dates. Maximum disease severity (26.0%) and least incubation period (2 days) were recorded at 30°C with 12 hour leaf wetness duration on cultivar Punjab Naveen. Disease severity was less (19.75 and 30.41%) when daily 4 hour side ventilation was given and it considerably increased (54.49 and 75.88%) when no side ventilation was given in both the cultivars, respectively. Cucumber yield was also affected with corresponding levels of disease severity under different treatments of sowing dates and ventilation hours. Of`the 11 fungicides evaluated, Ridomil MZ, Ridomil Gold each @ 0.25% and Amistar 25 SC (0.1%) proved highly efficacious with disease severity ranging between 7.10 and 10.28 per cent, respectively compared with 77.48 per cent in untreated control. Curzate M-8 @ 0.25% and Acrobat @ 0.25% % with 17.01 and 19.26 per cent disease severity, respectively, were next best fungicides against this disease. Fruit yield was also significantly higher in plots treated with these fungicides as compared to other fungicides and untreated control.