Damage potential of the broad bean beetle (Bruchus rufimanus Boh.) on seed quality and yield of faba beans (Vicia faba L.)

Abstract

The broad bean beetle (Bruchus rufimanus Boh.) is a serious pest of faba bean (Vicia faba L.) that threatens seed production in times of an increased demand for faba bean seeds due to the expansion of faba bean cropping area over the last decade. Three organic and three conventional field trials a year were conducted from 2019 to 2021 in three environmental different regions in Northern, Central and Southern Germany to test different control strategies and to investigate the bruchids' damage potential on seed quality and yield. The field trials show that organic cropping systems are more susceptible than conventional ones while no tested control strategy delivered satisfying and between years and test sites steady results. Neither yield nor thousand seed weight was influenced by bruchid infestation. However, germination of harvested seeds was highly linked with bruchid infestation, although the degree of correlation varied between years and cropping systems because of different climatic conditions during flowering and different high infestation pressures with fungal pathogens. Germination reduction by bruchid infestation occurs less as a result of damage to the embryo, but mainly as a result of increased susceptibility to fungal pathogens due to injured seed coats. In the trial period, infestation caused by pre-year's bruchids overwintering in stored faba beans was significantly lower than by bruchids migrating into the fields during flowering and the different infestation patterns had fundamentally different consequences for germination and therefore seed quality. Therefore, not the absence of living bruchids in the seeds is crucial for seed quality, but an as low as possible bruchid impairment of any kind.