Growing potatoes

Oxygen requirements of potatoes tubers are fairly high at 0°C, and least at 5°C.
They increase up to 16°C and are high at 25°C and above.

Therefore, oxygen deficiency of cells in the potato tuber center can occur at temperatures either too low or too high.
Injury develops in both the field and storage, particularly if air movement is restricted around tubers. Rapidly growing potatoes tubers have high oxygen requirements.

Black heart—blackening of the tuber center —follows acute oxygen deficiency associated with either low temperature in confined storage or high field soil temperatures.

Affected potatoes tubers rot later. Internal heat necrosis, a field problem, is a less acute high-temperature injury in which groups of cells become rust-colored, particularly in the centers of large potatoes tubers.

Internal heat necrosis is often severe in sandy or mucky soils exposed to solar heat following early vine death and delayed harvest.

Rot is usually not a severe problem. Potatoes tubers with oxygen deficiency symptoms should not be used as seed.

Avoid high field soil temperatures by harvesting promptly after vines are killed. Maintain cold storage at 4°C or slightly higher. Improve aeration in potatoes storage.

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Potato Mop-Top V irus (PMTV) occurs in areas with cool, damp conditions that favour spread of its fungus vector, Spongospora subterranea.

Symptoms of potatoes disease caused by Potato Mop-Top V irus Primary symptoms develop on and in tubers of some potatoes cultivars when they are infected directly from the soil.

Usually, only some stems on a plant are infected so that an affected plant also has normal-looking stems.

The virus survives in soil and spreads to new areas mainly through resting spores of the fungus vector, carried in soil or on seed tubers.

Management treatment of infected soil with calomel, sulfur, or zinc oxide can inhibit infection of a healthy potatoes crop. Roguing is useful with potatoes cultivars that produce strong symptoms.

(Alternaria solani) Early blight or Alternaria blight is worldwide in distribution and is one of the most important potato foliage diseases in areas with favourable weather conditions.

Symptoms of Early Blight Brown, angular, necrotic spots marked internally by a series of concentric rings form on leaves and to a lesser extent on stems.

Leaf lesions are seldom circular because they are restricted by the larger leaf veins. Lesions usually develop around flowering time and become increasingly numerous as plants mature. Lesions first form on lower leaves.

They may join and cause general yellowing, leaf drop, or early death. Tuber rot is dark colour, dry, and leathery.

Susceptible varieties of potatoes (usually early maturing) may show severe defoliation. Later maturing varieties may appear resistant.

Potato plants under stresses that hasten maturity (such as adverse environment, warm, humid weather, other diseases, or nutritional deficiency) become susceptible and die prematurely. Management Provide conditions for vigorous growth throughout the season, especially irrigation and fertilizer side dressing.

Organic fungicides sprayed on the foliage reduce the spread of early blight. Resistance is available among late-maturing varieties.

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(Streptomyces scabies)

Scab is a common tuber defect in most potato-growing regions, although usually not where soils are very acid.

The causal organism has been introduced into most potato soils. It affects only quality, not yield. Symptoms of Common scab Several types of lesions develop. They may be superficial or reticular, deep or pitted, or protuberant.

They vary in size and shape, but are usually circular and not more than 10 mm in diameter. They may coalesce so that most of the tuber surface becomes affected. Fibrous roots may also be damaged. Management Maintain high soil water levels compatible with good potato growth during tuber set and enlargement.

Avoid planting scabby potatoes seed tubers. Avoid repeated crops of potato or other scab-susceptible plants such as red beet, sugarbeet, radish, rutabaga, turnip, carrot, and parsnip (in these, the disease seldom has economic importance).

Scab-resistant varieties are useful. Maintain soil pH levels at 5 to 5.2 with acid-forming fertilizers or sulfur. Avoid heavy lime applications and preferably use dolomitic lime where needed.

“Acid scab” may be controlled with chemical seed treatments (mancozeb dust, 8%) or soil fumigation.

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