Brassica juncea powdery mildew epidemiology and weather- based forecasting models for India - a case study

摘要

A field experiment was laid out at S. K. Nagar and Bharatpur with Indian mustard (Brassica juncea) cultivars 'Varuna' and Local ('GM-2' at S. K. Nagar; 'PCR-7' at Bharatpur) sown on 10 dates at weekly intervals. Each plot was 1.5 m x 5 m size with a spacing of 30 cm x 10 cm, Recommended doses of N and P fertilizers were applied with no application of K fertilizer; insect-pest protection practices were undertaken viz., seed treatment with imidachloprid (5 g/kg) and spray 0.25 ml/1 oxydematon-methyl at15-day intervals. No protection was taken against any disease, First appearance of powdery mildew disease (Erysiphe cruciferarum) on leaves of mustard occurred during 50-120 days after sowing (d. a. s.)> with higher frequencies in later part of the cropperiod. Severity of the disease was favoured by > 5 days of > 9.1 h of sunshine, > 2 days of morning (maximum) relative humidity (r. h.) of < 90 %, afternoon (minimum) r. h. 24-50 %, minimum temperature > 5 °C and a maximum temperature of 24--30 °C. Regression analysis showed maximum temperature, minimum (afternoon) r. h. of the week preceding the date of observation were respectively positively and negatively correlated to disease severity both in cvs, 'Varuna' and 'GM-2' within the specified ranges, Models based on weather 1 week preceding date of observation for prediction of progression of powdery mildew severity at S. K. Nagar and Bharatpur were devised. Regional and cultivar-specific models could predict the crop age at which powdery mildew first appears on the crop, the highest mildew severity on the crop and the crop age at peak mildew severity at least 3 weeks ahead of first appearance of the disease on the crop, thus allowing growers to undertake timely fungicidal sprays. Models that stood the test of validation are reported.