Gnomonia Leafspot

Gnomonia infects leaves causing brownish to purplish lesions that begin small but expand to large areas, especially as lesions coalesce to form large blotchy areas of damage on leaves (Figure SS-1). Lesions can have various shades and are visible on the upper and lower side of the leaf (Figure SS-2). These spots often occur on the end of a leaflet and are V-shaped. As the disease progresses, the outer leaves of affected strawberry plants often die. Frequently, the lesions have small raised bumps, or pycnidia, visible with a 20 to 30x hand lens. If these bumps are not visible in the field, they emerge after a short time in incubation chambers (Figure SS-3). The pycnidia are have a yellow to brown color, ostioles (holes on top) and exude small conidia that have two oil bodies, one at each end of the conidia (Figure SS-3). The pathogen can also form sexual structures visible as black long necked and flasked shaped structures called perithecia often visible on leaf spots and petiole lesions.

Under favorable weather conditions, the pathogen causes a flower blast where flowers are heavily colonized by the pathogen turning the calyx, peduncle and other flower parts brown. In some cases, the pathogen colonizes the stem of the fruit causing stem-end rot (Figure SS-4) characterized by circular to irregularly shaped brown lesions. Fruit may be infected at all stages of development.