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THIS WEBSITE BELONGS TO CENTRAL TOBACCO RESEARCH INSTITUTE,RAJAHMUNDRY, INDIAN COUNCIL OF AGRICULTURAL RESEARCH, AN AUTONOMOUS ORGANIZATION UNDER THE DEPARTMENT OF AGRICULTURAL RESEARCH AND EDUCATION, MINISTRY OF AGRICULTURE, GOVERNMENT OF INDIA

Control of Diseases

A. Diseases in Seed Beds

1. Damping off : Pythium Aphanidermatum

This is a fungal disease caused by the soil borne pathogen. It is the most common and serious disease in tobacco nurseries causing death of seedlings. Conspicuous symptom of this disease is the sudden collapse of young seedlings in patches leading to uneven stand. Brown watery soft rot of young seedlings, girdling of hypocotyls and finally toppling and death of seedlings leading to wet rot are the characteristic symptoms. The pathogen spreads quickly and affect the seed bed causing enormous loss of seedlings.

High humidity, high soil moisture, cloudiness, temperature below 24oC, continuous wet weather, location of nursery in low lying areas are the favourable factors for high incidence of damping off disease.

Cultural and Preventive Measures:
Chemical control

2. Black shank and leaf blight : Phytophthora parasitica var. nicotianae

This is a soil borne disease. It frequently occurs during mid nursery period causing leaf blight and blackening of roots and stems leading to death of seedlings. Water soaked brown to black lesions appear on the leaf. These patches enlarge and coalesce leading to wet rot of leaf tissue and midribs. Cloudy weather, prolonged dampness and temperature below 22oC are the favourable factors for sudden outbreak of this disease.

Cultural and preventive measures

Black shank can be controlled by following the same schedule suggested for `Damping-off'. Mc.Nair-12 or CM-12(KA) or K-326 which are black shank tolerant varieties are to be used in irrigated northern light soils.

Chemical control

Spraying Fytolan or Foltaf or Blitox @ 0.2% concentration when the seedlings are 50-60 days old controls leaf blight. Ridomyl MZ 72 W.P. @ 0.2% can also be used to control this disease.

3. Collar rot : Sclerotium rolfsii

Just like damping off, sudden death of seedlings in patches is noticed in seed beds. Blackening of the collar region, wilting and rotting of leaves are the symptoms.

Control measures

Spraying 0.4% Bordeaux mixture or 0.2% Ziram or 0.2% Blitox, 3 weeks after seed germination. This is to be sprayed twice or thrice at weekly intervals depending upon weather conditions.

4. Leaf spot diseases


a. Anthracnose : Colletotrichum tabacum

This disease can be seen in any stage of the nursery. It will cause heavy loss to the nursery when favourable conditions to the fungus prevail. Small, light green to white water soaked lesions develop on young leaves. These lesions enlarge in wet weather to form oily, circular spots of 3 mm diameter. The spots dry up, become papery, thin, grey white surrounded by brown border. Effected leaves become wrinkled and distorted. Elongated, black or brown lesions on the midrib and petiole are seen in severe cases. On the stem, several elongated or oblong sunken brown lesions develop making the seedlings unfit for transplanting.

Optimum temperature for the occurrence of this disease is 18oC. High relative humidity, reduced light and overcast weather are favourable for the outbreak of this disease.

b. Frog-eye spot : Cercospora nicotianae

Generally this disease is seen 4-5 weeks after germination. Brown, round spots resembling frog eye form appear on the lower leaves of the seedlings. Spots appear first on basal leaves and gradually spread to upper leaves. Spots are small, circular, brown or tan with grey centres. In severe cases coalesce to become bigger spots leading to drying up of leaves.

Frequent waterings and wet weather leading to high humidity and temperature around 27oC are favourable for the development of the disease.

Control Measures

Spraying with Carbendazim 50% (Bavistin, Dhanustin, Jekestin 50 W.P. etc.) 3 gm in 10 litres of water at 30 days and 40 days after germination controls this disease. If necessary another spray has to be given after 10 days.

5. Root-knot nematode: Meloidogyne javanica/ Meloidogyne incognita

The light soil nurseries are prone to this disease. Root knot is caused by nematodes and prevalent in most of the light soil nurseries. Sandy soils and red sandy loams with adequate soil moisture favour the disease development. Several weeds growing in and around nurseries are alternate hosts of root knot nematodes. They are responsible for build-up of the nematodes in the soil.

Characteristic symptoms of root knot disease are yellowing of leaves, stunted growth of seedlings, wilting of plants, premature death of seedlings leading to bald patches in seed beds. Affected seedlings when pulled out show several galls on the roots. Galls vary in size, coalesce and produce multiple galls which give the seedlings a sickly appearance. Root knot affected seedlings do not establish well in the field resulting in heavy gaps.

Control Measures

6. Tobacco Mosaic Virus : Mormor tabaci

This is a contagious disease caused by virus. The infested leaves show characteristic mottling with light and dark green patches and seedlings are stunted.

Control Measures
B. Diseases in field crop

Black shank : Phytophthora parasitica f. nicotianae

This is a soil borne disease and it occurs when there is heavy and continuous rainfall, high soil moisture and relative humidity. The blackening of the stem of the diseased plants is noticed upto 30 cm height from the base. At the blackened portion inside the stem, the pith transforms into black round plate like discs. Roots also will be blackened, becomes soft and finally rottening is seen. The leaves of the effected plants becomes yellow, wilt and finally plant dies.

Control Measures
LEAF SPOT DISEASES
a) Frog eye spot : Cercospora nicotianae

The causal agents, symptoms and favourable weather conditions are the same as described under nursery diseases. In addition, this disease also appears as minute dark brown or black spots on stems, midribs, flower stalk and capsules.

Control Measures

Spraying Carbendazim (Bavistin/Dhanustin/Jekestin etc.) @ 0.03% (3 gm in 10 litres of water) at 15 days interval, commencing from 30 days after planting, effectively controls frog eye spot disease.

b) Brown spot : Alternaria alternata

Brown spot is a major disease affecting both FCV and non-FCV tobacco's in India. It is prevalent in most parts of India. This disease generally occurs when there is high relative humidity and atmospheric temperatures around 20-25oC. Especially when dew fall is more, more number of spots will be seen on the leaves. Dark brown or burnt spots separately or coalesced, appear on the diseased leaves. The spots will be like small water soaked spots first, later gradually grow to one cm size in 5-6 days and turns to brown colour. Sometimes yellow rings are seen around the spots just like frog eye spot. When the spots are closely observed, there will be circular rings on the spots. The disease will first appear on the lower leaves and gradually spreads to the upper leaves. Affected leaves dry up and do not cure properly. Dark brown, sunken, elongated spots appear on stems, petioles, seed capsules and stalks also.

Control Measures

Dithane M 45 or Indofil M 45 @ 20 g in 10 litres of water in combination with plantamycin or streptomycin or streptocyclin 3 gm is to be sprayed on the crop such that all the leaves are covered. For this high volume sprayers like sikar or hi-tech or knapsack sprayers should be used. Depending on the intensity of the disease, two or three sprays should be given at weekly or 10 days interval. Use of excess doses of nitrogen fertilisers should be avoided.

Broomrape (Orobanche) : Orobanche cernua
It is a complete root parasite affecting the yield and quality of tobacco. The shoots emerge in clusters and their basal portion is attached to tobacco roots through which it draws nourishment and depletes the host resulting in yield loss of 24 to 52%. Affected plants become stunted, leaves turn pale and wilt. Initially leaf tips droop and as the attack intensifies, all the leaves wilt. High soil moisture due to irrigation or rain after planting, low soil temperature during winter months encourage heavy incidence of Orobanche.
 Control Measures
Leaf curl virus: Ruga tabaci
This virus is transmitted through whitefly. Different types of viruses cause different symptoms. With mild types the leaves show slight wrinkles and drooping. In case of severe types the leaves and stem curls and leaves become thick and shrinkled and unfit for curing. Sometimes enations are also seen on under side of the upper leaves.
Diseased leaves show vein clearing, puckering of leaves, downward curling of leaf margins; leaves become brittle; thickening of veins. Since whiteflies spread disease, conditions such as too much bushy vegetation around tobacco fields serve as breeding places for whiteflies and thus spread the disease. Growing of brinjal, sunflower nearby tobacco fields also encourage build-up of whiteflies.
Control Measures

 

  Spraying has to be done preferably in the evening hours (4-6 pm) with high volume sprayers and it should be ensured that the both sides of the leaves also are covered. Further the spraying schedule has to be adopted on community basis.
Tobacco Mosaic Virus: Mormor tabaci

The leaves infested with tobacco mosaic virus show dark or light green patches. This is a contagious disease. This disease spreads through contact by labour and implements used for interculture. If the plants are infected in the early stages they show stunted growth reducing the yield and quality considerably. If the disease occurs when the crop is full grown, the tobacco yields are not affected.

Unclean cultivation, indiscriminately touching diseased and healthy plants, use of tobacco products by workers while working in field, presence of susceptible weeds and crop plants near fields are some of the factors responsible for disease development.

Control Measures
Root-Knot Nematode: Meloidogyne javanica

This is most prevalent in tobacco grown in light soils. Nematode infested plants do not grow vigorously and show stunted growth. The leaves become yellow in colour. In severe cases the plants die.

Control Measures

In root-knot affected fields, crops like groundnut, marigold, gingelly, chillies, cotton, redgram are to be grown for two seasons. Deep summer ploughing of the field also helps in reducing the incidence of root-knot.

Root Rot: Fusarium Wilt

In FCV tobacco grown in Northern light soils and in burley tobacco grown in agency areas now a days this disease is seen. The leaves on one side of the plants lose vigour and wilt like paralysis on the affected plants with this disease. Gradually complete plant will be affected and finally the plant dies. Initially the root tips show rottening and gradually all the roots rot. The leaves become yellow in colour. The plant will finally die due to lack of supply of water and nutrients.

Control Measures

This disease can be controlled by pouring 75 to 100 ml of calyxin 0.05% solution (calyxin 10 ml in 20 litres of water) at the plant bases of infected plants and the surrounding plants. This solution should not be sprayed on the plants.

or

By pouring a mixture of Dithane M45 20 g and carbendazim (bavistin) 5 g in 10 litres of water at the plant bases of infected plants and surrounding plants @ 75 to 100 ml. This solution can also be sprayed on the plants.

Powdery mildew : Erysiphe cichoracearum
Control Measures