Gordon Johnson, Extension Ag Agent, Kent Co.; gcjohn@udel.edu
With the recent snow it is hard to believe but potato planting season is right around the corner. In most years, the first potatoes are planted around St. Patrick’s Day (March 17) in Delaware or soon after. One of the most important factors in growing a high yielding potato crop is to plant seed pieces from quality seed potatoes. This will lead to better stands and more uniform emergence. Some seed potatoes have already arrived in the state, other loads will follow soon. The following are some pre-plant considerations relating to seed potatoes.
● Purchase high quality certified seed potatoes from a grower that you have developed a good relationship with. Ask about last year’s growing conditions and how the seed potatoes performed (yields, visual quality, plant health, stress). Take a visit to your seed supplier every couple of years to see their operation and evaluate the potatoes in storage. Tuber physiological age in seed potatoes is affected by growing conditions and to a larger extent by storage temperatures. Seed potatoes stored at higher temperatures have aged, are considered older, and will behave differently than seed potatoes stored at lower temperatures where tubers have not aged as much and are considered young seed. Seed that has been “aged” so that it is older from a physiological standpoint will emerge more quickly, have more stems per plant, set tubers earlier, have more tubers, have smaller tubers, and have better early yields. This aged seed should be used for earlier plantings and to obtain early harvest dates to hit early markets. Seed that has not been aged is considered young physiologically. This seed will emerge later, have fewer stems, set fewer tubers, have larger tubers, and mature later. Overall tonnage will be higher. Use younger seed for later plantings and to obtain higher numbers of large or “Chef” sized potatoes.
● Inspect all incoming loads well. Note any signs of rots (dry rot, soft rot), other tuber diseases (silver scurf, scab), storage problems, freezing, bruising, or other defects and reject any loads that are sub-standard.
● Minimize bruising of seed potatoes during handling. Bruising is one of the major factors affecting seed performance.
● If seed potatoes are to be stored for any length of time before cutting, keep at 40-42°F in well ventilated conditions at 85-90% humidity. Separate bins are recommended for different lots.
● Warm the seed 7 to 10 days prior to cutting at a temperature of 55°F. This lowers levels of certain sugars and initiates bud break. Provide good air circulation and a humid condition. Warming time should be adjusted according to variety. It is important to avoid excessive sprouting. Another option is to cut the seed first and then warm it 7 to 10 days prior to planting. There is a somewhat higher risk of loss from rots using this method, but it has some advantages. Precut seed should be piled no more than 6 feet high at temperatures of 55-65°F with plenty of air for drying and wound healing. Humidity should be 85-95%. Precut warmed seed that has been allowed to heal for at least a week emerges more quickly, has better stands, and leads to increase yields (studies have shown 10% or better yield increases compared to fresh cut and planted seed).
● Use a clean, disinfected cutter (or clean knives if hand cutting). Keep the blades sharp and adjusted to deliver an average seed piece weight of about 2 ounces. Clean and disinfect cutting equipment, preferably each day and definitely between seed lots. Note any signs of internal diseases during cutting and discard bad lots. An 8 ounce tuber will produce the highest percentage of good seed pieces with the least waste (range between 6-10 ounces is acceptable). All potatoes should be fungicide treated after cutting. Whole B seed potatoes can be planted without cutting if sized properly but still benefit from fungicide treatments.