Risk factors

Silver scurf on potato tubers is usually visible after harvesting although the primary infection has occurred earlier, in the field.

During the growing cycle of the potato, the seed tuber has usually been considered as the main source of inoculum. But today, there is sufficient evidence to show that soil residues of numerous plants, crops and weeds can also play a role in the dissemination process by hosting and maintaining the infectivity of the fungus during its winter resting phase.

At harvest, a prolonged delay (more than 4 weeks) between haulm destruction and harvest increases the risk of tuber infection.

During storage, temperatures below 5°C inhibit fungal growth but this is not compatible with tuber quality for the fresh market. Ventilation and relative humidity in storage are the other factors necessary to control fungal growth. Efficient ventilation can reduce excessive moisture but this may encourage uncontrolled sporulation and dispersion of the spores present in the storage areas and/or on the tubers which can act as primary inoculum on healthy tubers. No chemical control is possible at this stage.