In 1996 it killed blossoms giving much the same appearance as blossoms blighted by brown rot, Monolinia laxa. This fungus penetrates deeply into the hull and shell, and finally into the kernel. The infected and dead nuts have characteristic orange-brown fungus spores in the lesions on the surface of the nuts. It is sometimes possible to see the orange spores in the kernel itself. Infections in young fruit rarely exude gum, but half-grown and larger nuts gum profusely, and clusters of nuts can be glued together.
Infected leaves show a marginal and blotchy necrosis.
The fungus over winters in the shrunken nuts and in the peduncles, or nut stems. After harvest, very gummy, shrunken nuts are easy to find tightly sticking to branches of the very susceptible varieties such as Merced. Merced, Monterey, Price, Butte, Thompson, and Ne Plus are the most susceptible varieties, but Fritz, Harvey, Mission, Padre, and Carmel can be badly infected. Nonpareil will show some infection in very wet springs, but is probably the least affected variety. In Australia the Fritz is one of the most diseased varieties, with Peerless, Carmel and Ne Plus very close behind.