Seed potatoes should be essentially free from seed-borne diseases including Fusarium dry rot (shown here), which can cause poor emergence and serious economic losses. Compared to middle-aged seed, young seed is more vigorous but tends to emerge slower, to produce fewer but larger tubers, and to mature later. If you have young seed, then you have the flexibility to choose whether you want to plant young seed or to use warming and/or cutting practices to move the seed toward middle age. Mike Wind of Windiana Farms near Taber, Alta., grows chipping varieties and Russet Burbank for the french fry industry. He has developed a set of seed prep practices that have been working well for their farm for about the last 10 years. His tip for seed selection is to know your seed source. “Your relationship with your seed supplier is very important.” “We like to bring our seed in five weeks before planting, if possible. That way we can get the temperature of our seed where we want it,” he adds. Potato pathologist Khalil Al-Mughrabi, with the New Brunswick Department of Agriculture, Aquaculture and Fisheries, offers tips for when the seed is delivered. “Before bringing seed onto a farm, all machinery, cutting knives and equipment [that will come in contact with the seed] should be disinfected,” he says. “Growers should visually inspect seed potatoes within 24 hours of delivery. Any signs of a disease in the seed should trigger a red flag. Send a sample to your extension service department to have a formal diagnosis done. Growers can cut a sample of tubers and look for rot symptoms. A buyer has only 24 hours to request a re-inspection after delivery. Some growers ask for a test certificate indicating freedom of the seed lot from late blight.” Warming, cutting, precutting Even though cutting is a common seed preparation practice, Banks sees a lot of advantages to planting whole seed. “Cut surfaces provide points of entry for bacteria and fungi. While there are seed “Growers should visually inspect seed potatoes treatments for fungal pathogens, mainly Fusarium dry rot and Rhizoctonia, there within 24 hours of delivery. Any signs of a disease in are no treatments for bacterial pathogens the seed should trigger a red flag. Send a sample to like blackleg and soft rot, which can cause poor emergence in wet years. In addition, your extension service department to have a formal cut seed is not recommended for varieties diagnosis done. Growers can cut a sample of tubers that have most of the eyes concentrated and look for rot symptoms.” near the bud end and only a few eyes near the stem end. Cutting these varieties results 10 TOP CROP MANAGER/POTATOES IN CANADA | Spring 2018 in many blind seed pieces that will not produce plants,” she says. “Planting whole seed eliminates the cost of cutting. Whole seed is also more tolerant to the stresses of high soil moisture and low soil temperature. However, whole seed is more expensive because of the extra grading required to produce seed lots of uniform tuber size.” Nevertheless, she notes, “Ontario potato growers are successful in cutting, treating and planting potato seed. Trials comparing whole and cut seed do not usually find differences in marketable yield or tuber quality unless there was a cool, wet spring.” Before handling, the seed needs to be warmed up from its recommended storage temperature of three to four degrees. Warming helps prevent bruising, and it may also be needed to break dormancy and speed up crop emergence. If seed is to be cut, Banks generally recommends warming it to about 10 C a few days before cutting. “Warm seed not only cuts better with less tissue tearing, but is also more physiologically active and heals faster than cold seed,” she explains. “However, warming seed tubers for periods longer than two weeks or at temperatures higher than 10 C can result in excessive sprouting and physiological aging leading to lower yields, decreased tuber set, and smaller tubers.” Al-Mughrabi recommends grading the seed again after cutting to remove any tuber rot, and frequently disinfecting the cutting equipment using quaternary ammonium-based products. Banks adds, “Seed cutters should be cleaned and sanitized at least daily while cutting, and always before cutting a new seed lot.” The knives need to be kept sharp. The seed should be cut in blocky pieces, with a preferred size range of 1.5 to about 2.0 ounces (43 to 57 grams). For varieties with wider in-row spacing, the seed pieces should be slightly larger than 2.0 ounces. Pieces smaller than 1.5 ounces produce fewer stems. Very large seed pieces tend to have more severe bruising, which increases the risk of seed-piece decay, and to have poorer emergence and less vigorous growth. Controlling the variation in seed size is also very important. Banks explains, “A wide variation in seed piece size results in skips and doubles because of inconsistent feeding through the planter.” At MacAulay Farms Inc., near Souris, P.E.I., they grow Prospect, Shepody, Russet Burbank, Ranger Russet and Dakota Russet varieties, producing their own seed for some of these. They grade the seed in early to mid-April and then put it back into their temperature-controlled storage, keeping it at about 3 C until cutting time approaches. Then they let the seed gradually warm to about 7 C and cut the seed. “The majority of the potatoes are cut into blocky, good-sized seed pieces,” explains co-owner Paul MacAulay. “The seed is then treated and placed in bulk trucks with air moving through, for one to two days, before planting.” At Windiana Farms, they precut and treat their seed up to three PHOTO COURTESY OF EUGENIA BANKS.