Application of simulation model to devise iso-loss curves for stem borer and leaf rust incidence in wheat

Pest scenarios were framed for incidence of stem borer and leaf rust in wheat, presuming lowest to highest pest incidence at different growth stages of the crop. A Crop simulation model, Info Crop-wheat was coupled with damage mechanisms of stem borer and leaf rust. The model was calibrated and validated with the data of field experiments. The calibrated and validated model was then used for simulating various pest and disease scenarios at three locations, viz., Delhi, Barrackpore and Varanasi. Simulation results were used to devise iso-loss curves for stem borer and leaf rust individually and jointly for both pests. These curves showed combination of pest incidence and crop age, which resulted in same yield loss during different crop growth stages. These related pest damage levels to yield loss during various growth stages of the crop. Iso loss curves for stem borer revealed that crop became more prone to the pest with increasing crop age. Nitrogen application resulted in reduction of losses due to the pest up to 70-80 DAS. Likewise at Delhi and Varanasi, crop exhibited more proneness to rust incidence upto 60 DAS and nitrogen reduced losses due to disease. However crop showed more tolerance to disease with increasing crop age at Barrackpore. Iso loss curves for multiple pests (stem borer and leaf rust) were intermediates between the iso loss curves for stem borer and leaf rust individually. These related pest damage levels to yield loss during various growth stages of the crop. Such curves can be used for pest monitoring and knowing the damage potential of pest population present on the crop at a given crop growth stage. Hence based on economic value of different loss levels such curves can help in deciding the need for control measures. This would be useful in rationalizing pesticide application. These can also be used for monitoring activity of multiple pests on the crop.