A large part of the crop in the Klamath Basin is stored for fresh market or processing during winter and spring. All seed tubers are stored.
Designs for potato storage facilities can vary but have controls for temperature, humidity, and ventilation. Ventilation is essential during storage. It removes field heat, excess moisture that may condense on colder tubers, and carbon dioxide and heat produced by respiration; at the same time it helps provide even temperature and humidity within the storage area and oxygen to support tuber respiration. Uniform airflow throughout the pile is important.
To reduce the risk of rot developing and spreading during the storage season, have wet or rotting tubers and any foreign material removed from the incoming conveyors when filling a storage unit. Don’t mix "good" and "bad" lots in the same storage, and place lots with possible problems nearest the door so they can be removed without impacting other lots in the storage.
The storage period consists of four phases: post-harvest, curing, holding, and warming.
Treat russet type potatoes that are to be stored longer than three months where silver scurf has been confirmed.
During the first part of storage, hold tubers at a temperature of 50° to 55°F with relative humidity above 95%. These conditions favor rapid suberization of any bruises or cuts incurred during harvest and allow the skin of immature tubers to mature. Both of these processes increase the resistance of tubers to decay. Hold tubers under curing conditions for a minimum of two weeks, then lower the temperature by 0.5°F or less per day until the desired holding temperature is reached. Avoid condensation caused by bringing in warm supply air on cold tubers. If there is increased risk of decay, as with tubers injured by frost or tubers exposed to late blight or excessively wet conditions during harvest, store affected lots separately. Cool them to 50°F and dry them as quickly as possible with high flows of non-humidified air. Be careful not to over-dry the tubers because loss of tuber weight will occur.
For most of the storage time, hold tubers at the lowest temperature possible without affecting market quality. The following holding temperatures are recommended:
- chipping: 50° to 55°F; lower for cultivars resistant to cold sweetening
- French fries: 45° to 50°F; lower for cultivars resistant to cold sweetening
- fresh market: 38° to 45°F
- seed: 37° to 40°F
Maintain humidity high enough to keep tubers from drying and to avoid pressure bruising but low enough to prevent surface wetness. Some cultivars are more susceptible to pressure bruise; shallower piles may be needed to reduce the likelihood of pressure bruise. Remember that high humidity maintains pile weight, but condensation encourages disease. After proper curing, manage the humidity to prevent surface moisture on tubers. Always visit storages at least once a week to look for storage problems.
Higher temperatures and longer storage times can increase the severity of leafroll net necrosis.
Storing tubers below 43°F prevents multiplication of Columbia root-knot nematode, Meloidogyne chitwoodi. Storing below 50°F prevents multiplication of northern root-knot nematode, M. hapla.
If holding temperatures were lower than 50°F, letting tubers warm up to this temperature before removing them from storage reduces bruising. Allow the heat of respiration to warm tubers. Do not use warm air; condensation may occur on cold tubers, creating conditions that favor decay. Be sure to maintain humidity to keep tuber water content at the proper level. Tubers with lower water content are more susceptible to blackspot bruising. If excessive sugars have accumulated in tubers to be used for processing, warming above 50°F for three weeks may reduce the sugar to acceptable levels. Before cutting seed tubers, warm them at least 10 days at 50° to 55°F to increase their wound‑healing ability. Warmed tubers also cut more easily with less physical damage.