Evaluation of forewarning models for mustard aphids in different agro-climatic zones of India

Mustard aphid, Lipaphis erysimi (Kaltenbach), is the most serious pest of Rapeseed-Mustard which is known to be responsible for a tremendous loss in yield and oil content, under various agro-climatic conditions of India. Information support on aphid occurrence and intensity is necessary for effective management by the farmers in the mustard-growing belt. In this study, an effort is made to develop forewarning model using the field data on aphid for 12 consecutive rabi seasons from 2003-2004 to 2014-2015 under different agro-climatic locations in India. Three main components of aphid-related stages were identified for which necessary forewarnings were needed to be issued: (1) severity, (2) the time of reaching the economic threshold level (ETL) for decision-making on pesticide application, and (3) time of occurrence of peak population. To address these, three different models were developed/used and validated using incident field dataset. Those field observations when the infestation level were below severe category (< 60) during rising phase of the aphid population were found to indicate highest R sqr. (0.82) for the model-I during validation. When model-II was used, 11 out of 14 locations (78.57%) stood validated. The assumptions made in model-III also got validated when humidity thermal ratio (HTR) of the week of peak population ranged between 1.5 and 4 (lowest among the weeks considered), and population reached severe category. The models showed better results during real-time validation in seasons 2016-2017 and 2017-2018, thus suggesting that these three models can be used to ascertain the severity, week of ETL, and week of peak aphid population for Brassica juncea varieties all over the mustard belt in India and can be operationalized spatially to forewarn against the aphid pest population in future under Gramin Krishi Mausam Sewa (GKMS) scheme.