Proper chemical treatment of seed controls some of the diseases which weaken or kill the sprout before or during emergence. It is an inexpensive insurance that partially protects against invasion by microorganisms in the soil and those on the tuber surface; however, chemical treatment usually only controls those microorganisms attacking the seed surface.
Cut seed tubers require lots of attention. While potatoes are being cut, periodic disinfection of cutting and handling equipment is recommended, especially between different seed lots. Where cut seed is not planted immediately, very specific environmental conditions for storage must be provided:
- Use a dust type seed treatment.
- Use forced air circulation through the pile of tubers (the pile should not be more than one meter deep).
- Hold at a temperature of about 12-15oC and a relative humidity of 85 95% for at least three days in order to suberize or cure the cut sets.
Ventilate intermittently only to provide enough air to dissipate carbon dioxide and heat from respiration and uniformly distribute temperature in the pile. After the curing period, maintain high humidity and reduce temperature to 5oC. Seed must be rewarmed before planting to ensure vigorous sprouting.
For chemical seed piece treatment recommendations, see Publication 1300A.
Planting for Better Plant Stand, Yield & Quality
The establishment of a uniform crop, which will develop and mature evenly and produce a regularly sized run of tubers, largely depends upon optimization of the preplanting activities and the planting operation itself. These activities include: seed preparation and sizing, seed treatment and cutting, equipment adjustment and proper operation of planting equipment.
When evenly sized, prepared, and cut seed pieces are appropriately placed in the seed furrow an effective plant stand will be established.
The potato planting season extends from late April until early June, depending on location and climatic conditions, April planting is very limited by frost potential and wet soils in most locations of the region.
Potatoes should be planted as early as conditions permit but soil temperature should be at least 7oC. Planting in cold or wet soils will delay emergence, increase the chance of seed piece decay and result in poor plant stands. Properly conditioned whole seed or well suberized cut seed should always be used. This is especially important when planting conditions are less than ideal; i.e., cold, wet soil.
A between-row spacing of 91 cm is common, with seed spaced anywhere from 15 to 40 cm apart within the row. The closer spacings are used for seed crops to keep tuber size small, whereas the wider spacings result in production of larger tubers required for the fresh market and for processing. The variety, soil fertility, soil moisture and length of the season will also influence choice of spacing. Seed of a variety prone to produce tubers with hollow heart should be planted at a closer within-row spacing.
The planters currently used include the automatic pick-type, the assisted feed, cup and tuber unit types. The pick-type is fast and operates most efficiently for uniform blocky seed pieces. However, punctures made by the pickers may spread tuber borne diseases from one seed piece to another. The assisted feed type, while slower and requiring more labour, allows greater placement precision ensuring better stands. The cup type, like the assisted feed type, reduces the spread of any disease which may be present. Cup type planters, though automatic, are sensitive to seed size and function best with uniform sized whole or cut seed. Tuber unit planters are primarily used by producers of Elite seed classes to meet planting requirements for certification.
It is important that planters be adequately cleaned and disinfected prior to use and in between fields. Proper mechanical operation contributes significantly to a good plant stand. Planters should be maintained in good working condition, operated at rates according to manufacturers' recommendations and run by competent persons.
No specific depth of planting will give equally good results under all conditions. Planting depths of 8 to 13 cm are recommended, but it is very important for good germination to place seed in warm, moist soil. Shallow planting can result in uneven emergence and contribute to some tuber greening. Excessive depth of planting may delay emergence, increase chances of disease and seed decay, reduce vigour and result in poor stand.
The numbers and size of tubers produced in the field is largely affected by the number of stems per unit of area. The greater the stem density, the greater in number and the smaller in average size are the tubers produced.
Small whole seed production requires a high stem density (over 30 stems/square meter). Tablestock and especially processing production require reduced stem densities.
Stem density is controlled by set spacing and the number of stems produced per set. The number of stems per set is influenced by the seed pre-treatment and seed size and variety.
For early market tablestock and processing potatoes, low stem densities are usually obtained by planting cut sets from larger tubers. In this manner, sets of 40 to 55 g having only a few eyes can be planted relatively far apart.
The close planting of whole tubers results in the multiple stems per set and high stem densities as is required for seed production.
CUTTING OF SEED
The shock of cutting seed reduces apical dominance, allowing additional sprouts to develop. Cut seed pieces have less eyes than whole seed of the same seed piece weight. Due to the shock of cutting, cut seed emerges earlier than whole seed which has not been subjected to a heat shock or presprouting.
Cleanliness and disinfection are most important in cutting seed to reduce the spread of any disease by the cutting knives.
The ideal situation is to cut seed ahead of time, and allow it to suberize under conditions of good ventilation, high humidity and a temperature of 12o-20oC. This is most important as the seed can spoil very quickly if these conditions are not met.