Incidence and Causes of Postharvest Fruit Rot in Stored Michigan Cranberries

The incidence of postharvest fruit rot and associated fungi was studied in stored cranberries in Michigan in 2000 and 2001. Ripe cranberries were harvested from eight commercial farms in southwest and northeast Michigan, including the Upper Peninsula. Eight cranberry cultivars were represented: Stevens, Searles, Le Munyon, Pilgrim, Ben Lear, Bergman, Beckwith, and WSU 61. Fruit rot incidence was assessed within 1 week after harvest. Remaining sound fruit was stored for 2 months at 5°C, and fungi were isolated from rotted fruit after 1 and 2 months of storage. Year and region, but not cultivar, significantly affected the overall rate of rot development in storage. Storage rot levels generally were lower in 2001 than in 2000, particularly in southern Michigan. A high incidence of field rot at harvest did not necessarily lead to a high incidence of storage rot. Storage rot tended to be more severe in the northern than in the southern growing region. Fungi most frequently associated with storage rot were Fusicoccum putrefaciens, Colletotrichum acutatum, Coleophoma empetri, Phomopsis vaccinii, and Phyllosticta elongata. F. putrefaciens was the predominant storage rot fungus in northern Michigan in both years and caused up to 80% fruit rot in storage. C. empetri and P. elongata also were isolated more frequently from beds in northern than southern Michigan in 2001. The cvs. Pilgrim and Stevens were more susceptible to storage rot caused by Colletotrichum acutatum, and Bergman and WSU 61 were more susceptible to storage rot caused by Phomopsis vaccinii than some of the other cultivars.