Effects of trifluralin, benomyl and metalaxyl on the incidence and severity of root disease in annual Medicago spp., and evaluation of cultivars for resistance to root rot

Abstract

The herbicide trifluralin increased both the incidence and severity of root rot in four Medicago truncatula cultivars and reduced their dry matter production. In glasshouse studies with a naturally infested soil from Kaniva, medic root disease was controlled by soil incorporation of metalaxyl but not by soil treatment with benomyl. The known biological activity of metalaxyl suggests that the fungi responsible for the root rot were Peronosporales. The same fungicides failed to control medic root diseases in a field trial at Dooen in 1984. Medic cultivars varied in their susceptibility to root rot, some having moderate resistance, although none were immune. The susceptibility rankings established in glasshouse tests with naturally infested soil were supported by field observations. The results show that there is potential for control of medic root diseases by selecting resistant medic cultivars.