Northern stem canker
(formerly Diaporthe phaseolorum var. caulivora)
Northern stem canker is a disease of economic concern that was first identified and confirmed in NY in 2014. Since the initial confirmation, it has been discovered to be fairly widespread throughout many soybean production areas in NY, though currently only at moderately low incidences. The pathogen survives on infected soy residue, and infection occurs during vegetative growth stages, but symptoms don’t appear until reproductive stages. Foliar symptoms include interveinal chlorosis, followed by necrosis, which is indistinguishable from the foliar symptoms of other soilborne diseases including sudden death syndrome and brown stem rot. Dead leaves remain attached to stems. Initially, small reddish-brown lesions appear, often near nodes on the lower stems, which expand into distinctive ‘cankers’ with slightly sunken, grayish-brown centers and reddish margins. Large cankers may girdle stems completely. Splitting stems longitudinally may reveal a browning discoloration of the vascular tissue and pith, often more pronounced near the nodes on the lower stems, similar to what is observed with brown stem rot.
The disease reduces the number and size of seeds produced, and could result in yield losses of up to 50% in a severe epidemic. It is important to note that there are two forms of stem canker;
- northern stem canker, and
- southern stem canker.
Southern stem canker has not been identified in NY. Each disease is caused by a different pathogen, and controlled by separate resistance genes. Because northern stem canker was dismissed as a disease of minor importance in the 1950s, most seed companies do not provide disease ratings specific for northern stem canker in their catalogs. Most ‘stem canker’ ratings in commercial seed catalogs are for southern stem canker, a disease of great importance to many soybean production areas of the U.S., but have no relevance to northern stem canker resistance. Foliar fungicide applications for management have shown inconsistent results, and may not be cost effective.
Tillage practices to bury infected residues and rotation with non-host crops, including small grains or corn, are recommended for highly infested fields if varieties with resistance specific to northern stem canker are not available.