Gray mold or Botrytis fruit rot is the most common and most serious disease of the Rubus species worldwide and is usually found on overripe and bruised fruit. The pathogen has a wide host range and overwinters in dead leaves and plant debris. The fungus rots fruit in the field before harvest, especially if rain occurs during blossoming. Most overripe and bruised fruit are susceptible, especially red raspberries. Aging leaves are also attacked, giving rise to cane infections.

Symptoms

Infections in the spring can be observed on canes, appearing as bleached-out, whitish areas. Infected berries become covered with masses of fungal spores, which give the disease its characteristic name "gray mold." If not harvested, infected berries become mummified and remain attached to the plant, which can serve as additional sources of inoculum in the planting.

Disease Cycle

The disease cycle of Botrytis on brambles is the same as that on strawberry. See "Gray Mold of Strawberry" fact sheet.

Control

Cultural practices that create an open plant canopy, improve air circulation, increase light penetration, and speed the drying of plant surfaces after rain aid in the control of the disease. It is important to avoid an excess of nitrogen fertilizer and the elimination of weeds help maintain an environment less susceptible to gray mold. It is also important to harvest fruit before it is overripe.