Evaluation of foliar and seed treatments for integrated management of root rot and pea leaf weevil in field pea and faba bean

Abstract

Increased production of field pea (Pisum sativum L.) and faba bean (Vicia faba L.) in Canada has led to a greater incidence of disease and the range expansion of insect pests. Several soil-borne pathogens cause root rot in these crops, while the feeding activity of the pea leaf weevil (Sitona lineatus L.) significantly reduces nitrogen fixation. As pathogens and pea leaf weevil larva are associated with the roots of their mutual host, there is potential for synergistic interactions to occur that may ultimately reduce yield. Field trials at three locations in southern Alberta in 2016 and 2017 evaluated the use of insecticidal and fungicidal seed treatments, a foliar insecticide spray, alone and in combination, and nitrogen amendment as strategies to reduce impacts of both root rots and pea leaf weevil. The fungicides ethaboxam and fludioxonil did not reduce disease severity in pea or faba bean during the two-year field study. Quantitative PCR assays demonstrated that the pathogens Aphanomyces euteiches and Fusarium spp. co-infect pea roots under field conditions, but pathogen levels were not consistently reduced by any of the treatments. The insecticide thiamethoxam reduced nodule and foliar herbivory, whereas the foliar insecticide, lambda-cyhalothrin, and nitrogen fertilization at seeding had no consistent impact. No single or combined treatment protected yield or seed quality, therefore an effective method of managing these constraints to pea and faba bean production is still required.