Judicious spray against cabbage butterfly for economical and sustainable cultivation of crucifers in dry temperate regions of North West Himalaya

Predictive regression equations between marketable yield and Pieris brassicae population at pre-treatment [pre curd initiation stage], 14 days after first (DAS₁) and second (DAS₂) spray [post curd initiation stage] were y = -0.336x + 22.76, y = -0.249x + 17.92, y = -0.440x + 15.05, respectively during first year and y = -0.036x + 14.00, y = -0.137x + 15.76, y = -0.331x + 15.21, respectively during second year. The corresponding coefficients of determination (R²) were 0.064, 0.981, 0.868 in 2008 and 0.014, 0.827, 0.957 in 2^nd year, respectively. Similarly, regression equations between marketable yield and plant infestation were y = -0.240x + 21.08, y = -0.303x + 22.83 at pre-treatment; y = -0.142x + 16.05, y = -0.202x + 16.37 at 14 DAS₁ and y = -0.346x + 15.31, y = -0.350x + 15.36 at 14 DAS₂ in two years, respectively. The related R² values were 0.069, 0.109 (pre-treatment); 0.883, 0.972 (14 DAS₁) and 0.860, 0.944 (14 DAS₂) in the respective two years. Insecticide sprays at post curd initiation stages of crop growth should be followed in highlands of Himachal Pradesh.