Most European growers plant small, whole seed tubers. An increasing number of Canadian growers are
planting whole seed (see Whole versus Cut Seed), but the most common practice is to cut whole seed tubers
into smaller seed pieces.
The object of cutting is to produce uniform seed pieces with an average weight between 1.75 and 2.25 oz
(50 and 65 g) (Figure 3.2-2). Growers should consult with their provincial potato specialist or processor
field staff for seed size recommendations. Some varieties (Shepody and Yukon Gold) have poor eye
distribution and larger seed pieces ranging from 2.25 to 2.50 oz (64 to 71 g) are recommended.
The majority of mother tubers in an uncut seed lot should be 8 oz (225 g) or less, with few tubers greater
than 10 oz (225 to 300 g). Growers should maximize the number of seed pieces with single cuts, and
minimize the number of tubers with two and three cut surfaces (Figure 3.2-1). This can only be
accomplished if the mother seed lot does not contain many tubers over 8 oz. Variation in seed piece size
results in variability of size, shape and yield of tubers from plant to plant.
Seed pieces weighing less than 1.5 oz (35g) are referred to as seed chips. The chip eliminator rollers on the
seed cutter should remove the seed chips because they result in unproductive plants. Improper chip
eliminator roller adjustment or overloading the cutter are the main causes of excessive numbers or chips in
a cut seed lot.
To reduce seed piece infections, cutter knives must be kept cut surfaces that are easily infected with decay
organisms. Cutters should be disinfected at least once a day or between every seed lot. Pay special
attention when disinfecting the rollers as they tend to hold pathogen-laden debris. If seed is handled or cut
at a temperature of 45°F (7°C) or less, the incidence of shattering bruising may increase and cause seed
decay.
Seed piece fungicide treatments should be applied to all seed lots immediately after cutting. Growers must
assess field location and seed source histories to determine which fungicide seed treatment to apply. Seed
treatments effective against late blight are recommended if the seed originated from an area where late
blight was reported. Other seed-piece treatments that control Rhizoctonia sp. and silver scurf are
recommended when seed or field location indicates a risk for disease inoculum.