A systematic methodology to assess bruchid field infestation and the impact of field-carry-over infestation in stored pulses

Bruchids (Callosobruchus spp.) are serious pests of stored pulses whose incidence starts at field level and field-carry-over infestation persists in the stores. The temporal occurrence of bruchid infestation on standing crop and its subsequent impact on stored pulses has not been worked out in most of the pulses. A systematic methodology was developed to identify the crop stage where bruchids initiate the primary infestation on standing crop (i.e. infestation window) and its subsequent losses at storage level arising due to field-carry-over infestation. In this methodology, the observations on pest infestation on seeds/pods were recorded at definite intervals from open and caged plants starting from the first week after flower initiation (WAFI) till harvesting of mungbean, cowpea, and pigeonpea. Further, during storage, the observations were also recorded from grains harvested from the open and caged plants representing each interval and stored in cloths bags separately and observed on a bimonthly basis for one year. Results revealed that the field infestation on the seeds/pods started from 3, 4 and 7 WAFI in mungbean, cowpea, and pigeonpea, respectively. The infestation was found to be incremental towards crop maturity and overall, the infestation on the pods at field level did not cross 6 per cent. The results obtained through systematically designed methodology explicit the timeline of bruchid infestation at field level and the impact of field-carry-over infestation under storage conditions. This can help to identify and intervene a timely management programme in the existing IPM schedule to break the bruchid field-carry-over chain.