The first signs of seed piece decay on potatoes are reddish brown to black spots that slowly form depressions on the surfaces of cut seed pieces. Later these spots may become black and slimy from bacterial infections. Entire seed pieces will rot and fail to emerge if enough infections develop. Seed piece decay reduces stands, results in variable plant size, and may increase the incidence of blackleg.
Life cycle
Seed piece decay is usually caused by the combined action of the Fusarium fungi that cause dry rot in potatoes and the Erwinia bacteria that cause blackleg, although decay can sometimes be caused by Fusarium alone. Fusarium spores are present virtually everywhere in the soil. They germinate and infect the freshly cut surfaces of seed pieces, causing lesions that later may be invaded by Erwinia. When seed pieces are infected by both Erwinia and Fusarium, losses from seed piece decay are much greater than when Fusarium is present by itself. Cool soil that is too wet or too dry favors the development of seed piece decay.
Solutions
Plant only certified seed potatoes. Cut them when sprouts just begin to form and plant the seed pieces immediately. Plant when soil temperature is above 45°F.
For more information, see the Damping-off Diseases in the Garden Pest Note.
