Stem canker and dieback of Blueberries and Cranberries

Cranberry fruit rot is a disease complex that can be caused by several pathogens.
Stem canker and dieback symptoms caused by Gloeosporium minus were observed on highbush blueberry (Vaccinium corymbosum) for the first time in North Carolina. Symptoms first appear as dark-red, circular-to-elliptical lesions surrounding a leaf scar on young succulent shoots. As the cankers enlarge, affected stems turn brown, become gray, and die. By the second year, cankers range in size from 10 to 30 mm in length, and often result in severe dieback. Numerous black acervuli are produced over the entire lesion. Six blueberry cultivars tested were susceptible to G. minus, although resistance varied. The severity of the disease depended upon mode of infection and stage of plant growth. Invasion of leaf scars via attached petioles resulted in stem canker development. Penetration of nonwounded stems through the epidermis resulted in small raised lesions that failed to enlarge. A temp of 25-30 C was optimum for canker development and spore production. Histological observations indicated that the fungus apparently invades the xylem vessels of the stem only through vascular tissue of the leaf scar or flower buds. Death of the stem is apparently due to vascular occlusion by hyphae and tyloses. Penetration and infection of nonwounded stems through the epidermis results only in a fleck reaction.