2.2.96
DISEASE DEVELOPMENT, VARIATION IN PATHOGEN AND CHEMICAL CONTROL OF DOWNY MILDEW OF CUCURBIT

RV HIREMARTH and S ASHTAPUTRE

University of Agricultural Sciences, Drarwad, India

Background and objectives
Downy mildew of cucurbit caused by Pseudoperonospora cubensis is a serious threat to cultivation of cucurbits in well distributed rainfall areas of Karnataka, India. The disease has been reported to cause 61% loss in yield [l]. Since the pathogen has a wide host range on various species of cucurbits [2], studies were carried out on the variation in pathogen, development of disease and fungicidal control of the disease.

Materials and methods Development of downy mildew at weekly interval was studied on four species of Cucurbitaceae sown on two different dates for 2 ;years. Cross inoculation was carried out in potted plants in glasshouse either by spray inoculation or by stapling infected leaves. Nineteen varieties belonging to nine species were inoculated with the inoculum obtained from six varieties of three species.

Fungicidal control of the disease was by Metalaxyl MZ (metalaxyl 8% + mancozeb 64%) spray at different stages.

Results and conclusion
Observations on the development of the disease indicated that the disease became severe during the month of October. Wet weather followed by dry spell and higher humidity (around 90% r.h.) with a temperature range of 20-28C were found to be suitable.

Cross-inoculation studies indicated that the inoculum from different cucurbits was cross-inoculable to most other species of Cucurbitaceae, indicating that the fungus appears to be pathologically uniform. The possibility of existence of races within a geographical locality appears to be less likely.

Chemical control of Downy mildew on cucumber showed that the disease can be effectively controlled by seed treatment with Metalaxyl MZ followed by two sprays (0.1%) at 35 and 50 ;days after sowing.

Referenees
1. Ullasa Ba Amin KS, 1988. Mysore Journal of Agricultural Science 22, 62-67.
2. Bains SS, Jhooty JS, 1976. Indian Phytopathology 29, 214-215.