Dr Eugenia Banks is a potato specialist and works as consultant for the Ontario Potato Board in Canada. In a recent newsletter, she notes that second growth of potato tubers is a physiological potato problem induced by soil temperatures of 24 degrees Celcius or above, especially when coupled with water stress. “These two factors interact to limit the tuber growth rate causing second growth,” Dr Banks says. “Inadequate soil moisture alone does not result in the initiation of second growth. Heat and drought have prevailed during the 2018 Ontario growing season, which explains why second growth has been reported in some fields this season.” She points out that potato varieties differ in their susceptibility to second growth.
“European varieties appear to be more susceptible because they were bred and evaluated in countries were the growing seasons are rarely hot. It is interesting to see that the current heat wave and drought conditions in Europe cause problems that European growers had rarely seen before, but we are familiar with them here in Ontario. Our summers are the hottest in Canada, although Quebec has the same hot summers.”
According to Dr Banks, there are three distinct types of second growth – heat sprouts, tuber chaining, and secondary tubers (click pictures for larger view).
Secondary Tubers: Small tubers form on daughter tubers. The secondary tubers are formed on short sprouts or directly on the tuber surface. This disorder, also called little tuber disorder, is usually associated with physiologically old potatoes. High temperatures and water stress during the growing season are major factors contributing to the physiological aging of potatoes.
Cultural practices that promote uniform growth of plants and tubers throughout the season help minimize second growth, according to Dr Banks. Among them are:
● Do not plant physiologically old seed in cold, dry soil
● Space seed pieces as uniformly as possible at planting
● Apply an adequate amount of fertilizers.
● Maintain uniform soil moisture sufficient to meet crop needs.
Dr Banks says that an application of MH when the crop is close to being harvested will in most cases stop the problem.