Black dot a particular scourge of fresh market potato crops in GB this season

Black dot has been a particular scourge of fresh market crops this season, according AHDB Potatoes in the UK. Delayed harvesting has encouraged disease spread, increasing the crop’s exposure to infected soil and high levels of moisture. Here’s a reminder of why the problem has been so widespread. Black dot is a disease caused by Colletotrichum coccodes. There is evidence that microsclerotia (resting bodies) of the fungus can survive for many years in soil due, in part, to alternate hosts. It can infect weeds such as nettle, field bindweed and shepherd’s purse.  Survival is further enhanced by the presence of potato volunteers. Black dot can be both seed and soil-borne. Although seed-borne infection can cause disease in progeny tubers, soil inoculum poses a greater threat. Soil contamination is the main source of disease in a progeny crop. Disease risk should be based on evaluation of seed infection and, importantly, soil contamination for which a soil test is available. Black dot is commonly confused with silver scurf (Helminthosporium solani). More in the latest Storage Bulletin from AHDB