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Coping with frost-damaged potatoes Out in the Cold Diggin' In Diggin' In STORAGE | By Paul Bethke & Troy Fishler Underlying tuber flesh oxidizes with time and will appear gray after a few days. Frost-damaged tissue loses its structural integrity and feels soft to the touch as soon as it thaws. Within days of thawing, affected regions begin to shed soggy masses of formerly frozen tissue. Adjacent, non-frozen tissue remains viable, and a closing layer will form at the interface between healthy and frozen tissue if conditions allow. The threat of infection by pathogenic organisms is very high until wound periderm formation is complete. Strategies for managing frost-damaged potatoes are based on conventional best practices for storing potatoes. To begin with, consider not harvesting fields where frost damage is extensive. In some cases, crop insurance may be the best option. Potatoes from fields with extensive frost damage—such as those with a high incidence of pink rot or soft rot—are unlikely to store well. For chip and fry processing potatoes, explore options for running the material through a processing plant directly off the field. This option depends on whether the potatoes have undergone extensive cold-induced sweetening prior to harvest. Prolonged exposure to cold temperatures promotes accumulation of reducing sugars in tubers and dark color in finished products. Varieties differ in their resistance to cold-induced sugar accumulation, and those that are slow to accumulate sugars have the best chance of producing acceptable products after exposure to cold temperatures. For fresh market potatoes, packing and shipping directly off the field is unlikely to be a good option. It is very difficult to grade out frost-damaged tubers, and Rain and cold delayed potato harvest throughout Wisconsin in 2018. Many farms were still digging potatoes in late October and into November. Temperatures below freezing took a toll on numerous fields when potatoes suffered frost damage. No one wants to see another harvest like 2018, but perhaps there is value in reviewing the causes and consequences of frost damage and discussing strategies for managing frost-damaged potatoes. Frost damage occurs when tuber temperature drops below approximately 30 degrees Fahrenheit and tuber tissues freeze. Potatoes that are closer to the surface are more likely to experience freezing temperatures than those deeper in the soil. Green potatoes, which are at the soil surface, will undoubtedly be the first to suffer from frost damage. Low spots in a field collect cold air and are more susceptible to frost damage than higher elevations. Soil moisture content also influences the susceptibility of potatoes to frost damage. Soils with lower water content cool more rapidly than soils with higher water content. Multiple environmental factors, including strong winds, clear skies and low humidity, increase the likelihood of frost damage when temperatures drop to below freezing. Frozen potato tissue is no longer viable and cannot be healed. Rapid water loss begins as soon as the affected tubers thaw. Frost-damaged tissues develop wet patches on the skin as moisture leaks from lenticels. 34 POTATO GROWER | MARCH 2019