Botrytis Fruit Rot
Botrytis fruit rot or gray mold is the most common and most serious disease of Rubus species worldwide. The disease is caused by the fungus Botrytis cinerea. This pathogen has a wide host range and can survive on either living or dead tissue. It can overwinter on dead leaves, plant debris, and on the stems. 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 also are attacked, giving rise to cane infections.
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, remain attached to the plant, and can serve as additional sources of inoculum in the planting. Botrytis can also cause a cane blight and leaf spotting.
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. Avoiding excess nitrogen fertilizer and eliminating weeds help maintain an environment less susceptible to gray mold. It is also important to harvest fruit before it is overripe. If fungicides are necessary, they should be applied during bloom, with additional applications made during harvest if needed. Refer to Table 7.5 for pesticide recommendations.