Phoma stem canker (blackleg) of oilseed rape (canola) and other Brassica crops

Phoma stem canker (blackleg) of oilseed rape, Brassicas and radish is caused by two closely-related fungi, Plenodomus lingam and P. biglobosus (formerly Leptosphaeria maculans and L. biglobosa). Plenodomus lingam is more aggressive but P. biglobosus can also be damaging and resistance genes against one may not work against the other. Both survive saprophytically on plant debris and spread by wind-dispersed ascospores, rain-splashed conidia and infected seeds. Spores germinate on leaves to infect via stomata or wounds, producing leaf spots which release rain-splashed conidia. Additionally mycelium grows via vascular tissue of the plant to the stem, where stem cankers develop and reduce yield by disrupting water transport. Infections of the pods although rare, produce infected seed, which can spread the pathogen to new locations. Classical identification has been superseded by PCR and DNA sequencing. The disease is managed by crop rotation to separate crops from debris of previous crops, resistant varieties and fungicides. Fungicides have no effect once the fungus has reached the stem, so control aims to prevent leaf spotting. A mixture of at least two fungicide modes of action is recommended e.g. a DMI (Azole; FRAC code 3) and SDHI (FRAC code 7) or QoI (FRAC code 11).