Since many of the common storage diseases naturally occur in the soil, they are transported into storage with the tubers. It is essential, therefore, not only to heal the exposed wound areas to minimize pathogen penetration, but also to lower the temperature as soon as possible after storing, to minimize disease spread within infected tubers, as well as from infected to healthy tubers.

Experts say that the majority of storage diseases are partially or completely inhibited by storage temperatures below 7.2^oC (depending on the variety). At temperatures above 10.0^oC the growth and development of disease organisms increases dramatically augmenting the risk of total breakdown.

According to researchers from the University of California, the risk of breakdown is greatest just after the storage has been filled, especially during hot weather. Temperatures above 10.0^oC should also be avoided during long-term storage. The hatching of flies is also inhibited below 10.0^oC, so the presence of flies is a good indicator that the temperature is too high somewhere in the storage and breakdown may become a problem.

Wound Healing and Curing

The researchers explain that tubers are often bruised and cut during harvesting and pre-storage handling. Regardless of how the stored potatoes are to be marketed, wound healing is essential to minimize the entry areas for disease organisms. Healing proceeds most rapidly at temperatures of 15.5^oC to 18.5^oC. At this temperature and with a high humidity, a suberin layer (similar to a scab) develops in three to five days. Cell regeneration, or complete wound healing, can take place beneath this suberin within 10 to 20 days, depending on the condition of the potatoes.

When the spuds are placed in storage, rapid cooling can result in more rot-forming organisms in the tuber, because the entry points remain unhealed. Rapid cooling, particularly in the absence of adequate air, can also result in black spot and other potato damage.
The Canadian Horticultural Council (CHC) recommends that where the danger of soft rot exists, whether as a result of blight, frost, pinkeye, blackleg or excess moisture, the first priority is to dry the potatoes. “For mild to moderate rot, ventilate continuously with a relative humidity of 85-95%. For severe rot, ventilate continuously with a relative humidity of 80-90%. Do not allow the humidity entering the pile to drop below 80%. In some cases, this may take several weeks or even months. In cases of severe frost or disease damage, cool the pile to 8.0-9.0^oC and maintain at that temperature for three to four weeks before cooling down further to 3.0-4.0^oC. The low temperatures will keep disease organisms in check while enhancing the drying process.” CHC warns that if processing potatoes are involved, a decision will have to be made whether to accept the loss of color due to low temperatures or the risk of rot at the higher temperatures needed to maintain color.

You can read the rest of this article in the Autumn Issue of Potato Business Digital magazine, which you can access by clicking here.