Fungal wilt, wart, early blight, late blight, black scurf and leaf spot

disease of potato

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Fungal wilt of potato

Two TypesSclerotial wilt

Sclerotium spp

Fusarium wilt

Fusarium spp

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Symptoms: Initial symptom is the presence of wilted plants within a canopy of healthy looking plants.Water soaked lesions develop on the stemThick white moulds appear on the collar region of the stem.Later fruiting bodies developed which look like mustard seeds.

Causal organism : Sclerotinia sclerotiorum

Sclerotial wilt:

Common in the plains of Maharastra and West

Bengal in Kharif Potato crop

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Symptoms:Infection starts on the seed tubers and progresses to underground parts of the stem and rootsAffected plants show yellowing of margins of the lower leaves later progressing to the entire plantFinally the plant wilts completely

Causal organism : Fusarium oxysporum

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Fusarium wilt:

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Alternate period of wet and dry soil condition is favourable for disease Severity is more in sandy acidic soil

Epidemiology

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Crop rotation with non host crops.Seed treatment with mancozeb, carbendazim @ 0.25% Use organic amendment mixed with Trichoderma harzianum

Management

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Wart is widely distributed in temperate and high altitude tropical regions with cold and rainy climate. In India, it is most prevalent in Sikkim and West Bengal.

Wart of potato,(Synchytrium endobioticum)

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Symptoms:White to brown tumour like outgrowth develop on stem , stolon and tubers.Symptoms usually develop below ground, but under wet conditions may appear on stem and foliage.Tumours blacken with age and may rot due to secondary organisms.Above ground warts are green, reddish and purple depending on the variety.

Causal organism: Synchitrium endobioticum

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• Wart infected tubers should not be plnated • Restrict the movement of potato tubers from infected

to non infected region through quarantine regulation.• Grow immune variety such as Kufri Jyoti, Kufri

Jeevan and Kufri mathu.• Quarantine legislation should be strictly followed.

Management of wart disease

EpidemiologyIntensity of disease is affected by soil moisture, soil temperature and soil pH

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World wide distribution and one of the most important diseases under favourable weather conditions.Starts appearing on potato just before the initiation of tuberization.

Symptoms:Older leaves show brown angular necrotic spots marked by concentric rings Distinguished from the late blight by the absence of white cottony growth on the under surface of spots.

Causal organism: Alternaria solani

Early blight of potato

Alternaria solani

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The spots enlarge and coalesce to form large necrotic areas and the whole leaf dries up and hangs along the stemBrown, dry and brittle spots of limited size and a well marked outline helps in differentiations of the early blight from other foliage diseases of potatoIn tubers, lesions are dark brown, sunken and surrounded by a raised marginThe internal tissues of the tuber become reddish brown and leathery to corky in texture

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EpidemiologyDisease is severe in high temperature25-30 0C alternating with moist period and poor vigour of the plant Poorly manured crop show severe attackContinuous drought period checks the disease

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Management

• Spray the crop with Antracol, Mancozeb @0.25% at 7-10 days interval.

• Crop debris should be destroyed after harvest

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Late blight of potato (Phytophthora infestans)

Most destructive disease of potato. Any part of the foliage may be infected under cool and moist conditions. Complete destruction of the plants in the field takes place within few days under congenial weather conditions.

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SymptomsCircular to irregular water soaked faded green spots develop initially at the tip of the margin of the lower leaves which turn into brownish black lesions. On the undersurface of the leaves the lesions are covered with superficial whitish (cottony) fungal growth.The lesions on the petiole and stems are black coloured of indefinite length.

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• During moist weather, the blighted areas rapidly enlarge, quickly spread to tender and older plant parts.

• Under dry conditions enlargement of the lesions get restricted and the blighted areas turn black and dry up.

• Stem infection occurs at nodes and plant topples over.• In tubers purplish brown spot appear which spread to the entire

surface.• On cuttings, affected tubers show brown necrosis spreading

from surface to center.• Tubers rot in soil before harvest or during storage.

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Epidemiology :Excessive humidity (>90 %) coupled with suitable temperature (15-20 0C) and optimum soil moisture (15-20 %) are most favourable for disease development.

Continuous rain or light drizzle for 2-3 days followed by low temperature is suitable for disease development.

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• Use tolerant varieties like Kufri Badsha, Kufri Jyoti, Kufri Ashoka and resistant varieties like Kufri megha, Kufri Pukhraj

• Select healthy, disease free seed tubers

• Infected plant parts are to be removed and destroyed

• Harvest the fully matured tubers in dry weather

• Apply protective spray with Mancozeb @0.2% alternating with Metalaxyl @0.25% at 8-10 days interval. In rainy days sticker like Triton AE (0.02%) should be mixed with the spray solution.

Management

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SymptomHard, superficial, dark brown or black bodies known as sclerotia are seen on the surface of the tubers.

When the infected tubers are planted emerging shoots are killed.

Black scurf of Potato Rhizoctonia solani

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Young sprouts are very susceptible to infection. In older plants, brownish black sunken lesions develop on underground stems and stolon. Surface of the tubers have black bodies known as scurf which are not easily removed.The growth of the fungus on the surface of the tuber causes rusting of the skin.The tuber shows hard dry rot with browning of internal tissues.During storage the entire tuber is reduced to a spongy mass.

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Crop rotation preferably for 3years with cereals.Shallow planting followed by gradual filling up reduces damage.Avail seed tuber lots that does not contain scelotia.Sundry the tubers before planting.

Management

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Symptoms:Small, water-soaked circular spots 1.6-3.2mm in diameter first appear on the undersides of older leaves. The centers of the spots are gray or tan and spots have a dark brown margin.Spots may also appear on stems. Heavily infected leaves will turn yellow, dry up, and drop off.

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Leaf spot of potato (Septoria sp)

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Infected plant materials should be destroyed by burning Haulms of diseased crops are to be removed and burnt before harvest of the cropFungicidal spray preferably with Zineb @ 2g/lit at 15 days interval

Management (Septoria)

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