GROWTH CONDITIONS
Growth period: 95–150 days, depending on the type/variety, normally classified as
being either 1st early, 2nd early or maincrop.
harvest to allow the tubers skins to harden up, and so bruise less easily.
Day length: there are both short-day and long-day varieties of potatoes; the former
types are mainly grown in the tropics.
Temperature: varies greatly depending on the variety, though the optimum soil
temperature is about 20–25
virtually stops. The plants are frost sensitive, especially when young.
Rainfall: some varieties can produce a small yield with only 350 mm during the
growing season, though the optimum is about 25 cm per week during the growing
season. Drought can be disastrous for potatoes, especially if this occurs when the
tubers should be bulking up.
Altitude: in the tropics, potatoes grow best above about 1800 m. For most varieties
the maximum is about 3000 m, though some Andean varieties grow best at 2000–
4000 m.
Diseases: volunteer plants, including the tubers, should be removed from the field as
soon as possible, to minimise spread of diseases. The dreaded Potato Blight
(sometimes called Late Blight) is caused by the Phytophthora infestans fungus and
is the most devastating of all potato diseases. In many ways it was responsible for
the Irish famine in the 1840s. Symptoms are almost always seen on the plants to
some extent, but the disease really only spreads rapidly and causes loss of
production in warm and humid conditions.
Symptoms of Potato Blight: leaves develop irregular brown necrotic (dead) patches.
In warm, humid weather the whole plant becomes affected, the tubers becoming
rotten and horribly smelly. Tuber rot is more common in temperate than in tropical
regions. The disease is mainly transmitted by the fungal spores being carried from
plant to plant, suspended in air or water droplets; and also by infected tubers being
planted.
Spores can survive in the field even without a potato crop because they also live and
multiply on wild Solanum species and volunteer potato plants.
It can be controlled with fungicides—Copper Sulphate or “Bordeaux mixture”
works well, sprayed every 2–3 weeks during the growing season as a preventative;
resistant varieties are available, uninfected seed (tubers) only must be planted, and it
may be possible to choose the planting date to avoid warm, wet weather during the
later stages of the potato’s growth period. The haulm should also be burned off
and/or removed as soon as it becomes seriously infected.
- Bacterial Wilt—a very serious problem in that land which is infected with this
bacteria can never be used again for growing potatoes. Symptoms: the plants wilt,
despite a moist soil, and a white mass oozes from the base of the stem or tuber when
it is cut. Bacterial Wilt does not occur in Europe, but virtually all varieties grown
there are susceptible to it, so potato plant material should never be moved from
country to country unless it has been reliably certified to be free from this disease.
The only practical control is by using varieties with some resistance. In areas where
°C. The higher the temperature, the more the aerial parts
develop at the expense of tuber development. At about 30 C tuber development °
210 TONY WINCH
The haulm (1Ic) should be burned off or removed a few days or weeks before