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Late Blight

Symptom of late blight on the potato leaf.
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(Phytophthora infestans)

Late blight is disease occurs while growing potatoes and caused by Fungi.
Although control measures exist, late blight remains the most serious fungal disease in most major potato production regions.

Symptoms of Late Blight

Water-soaked lesions appear on foliage that, within a few days, becomes necrotic, turning brown when dry or black when wet.

Under damp conditions, white mildew like sporulation is visible, especially on the lower surface of leaves. A pale yellow margin often forms around leaf lesions. Lesions on stems and petioles are black or brown.

Stem lesions are brittle and stems frequently break at the point of the lesion. Under certain conditions, wilting can occur on stems with lesions.
Disease is favoured by temperatures between 10 and 25°C, accompanied by heavy dew or rain.
POtatoes tubers infected by spores washed by rain from the leaves and stems into the soil have brownish surface discoloration.

Sections cut through tubers show brown, necrotic tissues not clearly differentiated from the healthy portions. Later secondary rot organisms develop in blighted tissue and rots spread in storage.


Sources of inoculum are neighboring fields of potato or tomato, volunteer plants, and cull piles.

Riptide 6 Week Pest ControlThe last two sources can be removed. Soil survival occurs wherever the sexual stage (resting oospores) occurs as a result of the presence of both the A1 and A2 mating types, which can lead to early infections.

Once infection occurs in a field, control is a function of host resistance and spraying, mediated by the environment.

Potatoes growers should check with local extension agents for information on forecasting systems or spray schedules that maximize fungicide efficiency and resistance levels of cultivars. There are cultivars with various levels of resistance.
Both protective and systemic fungicides are available, but the latter should only be used according to regional or national strategies that have been developed to minimize the development of resistance in the pathogen.
To prevent tuber infection when growing potatoes, plants should be well hilled, foliage completely sprayed during the growth period, and vines permitted to mature and die naturally or be killed before harvest.

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Wart potato disease

(Synchytrium endobioticum)

Wart is potatoes disease caused by Fungi.

Wart or black wart is widely distributed in temperate and high altitude tropical regions with cold and rainy climates. It may cause considerable yield loss where races of the fungus occur for which resistance has not been introduced. The disease is often associated with powdery scab and does not develop in warm or dry soils.

Symptoms of Wart

Tumors of any size up to several centimetres may develop on stems, stolons, and tubers.

Symptoms usually develop below-ground, but under wet conditions they may appear on stems and foliage. Initially, tumors are white to brownish or of the same colour as normal tissue. Tumors blacken with age and may rot because of secondary organisms. Aboveground warts are green, reddish, or purple, depending on variety.


Varieties that are resistant to races of the fungus should be used. Reduce wart incidence with long crop rotations (5 years or more) in combination with resistant varieties.

Prohibiting the shipment of tubers, particularly seed from infested regions, is effective in limiting disease spread.

Seed of resistant varieties grown in infested soil can spread the disease as well as movement of infested soil or manure adhering to tuber surfaces, farm machinery, or other equipment.

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Powdery Scab Potato disease

(Spongospora subterranea)

Powdery Scab is  disease caused by Fungi meet while growing potatoes.
It is present in all potatogrowing areas in temperate zones and in the tropical highlands of Central and South America.

Symptoms of Powdery Scab

Powdery-scabThere are usually no aboveground indications of disease. Initial symptoms are small, light-colour, blister-like swellings on the tuber surface. At an advanced stage, these become dark, open pustules 2 to 10 mm in diameter or larger, containing a brown, powdery spore mass.

Lesions are variable in shape, mostly roundish, and fringed by broken skin. Root galls of up to 15 mm across may form. In large numbers, they reduce plant vigour. When galls are newly formed, their colour is similar to that of normal roots.

Later, as galls disintegrate, the colour rapidly darkens.


Soil fumigation with methane sodium is reported to control powdery scab. Planting in well-drained soils free of disease and a long crop rotation with grasses where disease occurs may reduce incidence.

Plant disease free potato tubers. Resistant potato cultivars exist and should be used.

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