Field Crops> Tobacco (Nicotiana spp.)> Diseases

There are a number of diseases of tobacco crop which causes considerable damage to the crop and affect both the yield and quality of the produce. Symptoms of some of the important diseases and their suitable control measures are given below.

Damping Off

This disease is caused by a fungus Pythium aphanidermatum. It appears in nursery beds with decay of seedlings at the soil surface. Small seedlings may disappear altogether due to complete rotting. In older seedlings stems become shrivelled at the collar by brown discolouration.

Control Measures: (1) Use raised seedbeds with adequate drainage to remove excess water during heavy rains.
(2) Rabbing the seedbeds with paddy husk in 15-20 centimetre thick layer.
(3) Spray the nursery beds with 0.2% metalaxyl (Ridomil) solution.

Black Shank

It is caused by a fungus Phytophthora parasitica var. nicotianae. It may occur in nursery as well as in field. Black lesions are produced on stems starting at ground surface; leaves droop and fall down. Plants rot and die.

Control Measures: (1) Over irrigation should be avoided.
(2) Rabbing the beds with paddy husk in 15-20 centimetre thick layer.
(3) Soil drenching with 0.2% Blitox solution.

Frog Eye Leaf Spot

It is caused by a fungus, Cercospora nicotianae. It appears late in nurs ery season (60 days) and any time in transplanted crop. Oval, brown spots with ash grey centres of white dead tissues appear on leaves in the nursery and later in the field.

Control Measures: (1) Remove the spotted basal leaves from seedlings.
(2) Spray nursery beds with 0.2% Zineb at frequent intervals.
(3) Spray the plants in the main field after transplanting with 0.03% Carbendazim (Bavistin).

Powdery Mildew

It is caused by a fungus, Erysiphe cichoracearum var. nicotianae. It appears in the field on transplanted crop. Affected leaves appear dusted with white powder in patches; under favourable weather conditions the entire leaf surface is covered. In the case of flue cured tobacco, affected leaves get scorched on curing and show brown patches and become useless for marketing.

Control Measures: (1) Remove powdery mildew affected basal leaves.
(2) Dusting of sulphur 200 mesh at the rate of 40 kg per hectare.
(3) Spray the crop with 0.02% Carbendazim (Bavistin) at the rate of 500-700 litres per hectare.

Anthracnose

It is caused by a fungus, Colletotrichum tabacum. It appears in nursery beds on all the above ground parts of seedlings. On leaves small irregular whitish spots develop which coalesce to form bigger patches; affected leaves dry. On stem, elongated brown lesions are seen girdling the stem. Affected plants turn pale and collapse.

Control Measures: (1) Rabbing the beds with paddy husk in 15-20 centimetre thick layer.
(2) Spray the nursery with 0.03% Carbendazim (Bavistin).

Leaf Curl

It is a virus disease transmitted by whitefly. Infestation takes place in nursery. The disease appears around 40-60 days on transplanted crop. Dwarfing of the plant and reduction of leaf size takes place. Curling of the whole or portions of leaves is the main symptom of this disease.

Control Measures: (1) Remove the affected plants and plant healthy seedlings.
(2) Destroy weeds harbouring whiteflies around tobacco fields.
(3) Spray systemic insecticides such as 0.2% Oxydemeton methyl (Metasystox) 25 EC or 0.1% Phosphamidon (Dimecron) 85 SL.

Tobacco Mosaic

It is the most widely distributed virus disease on tobacco. Injury is caused both in nursery as well as in field. Diseased plants show leaves with mosaic pattern of light green and dark green areas. There is typical mosaic mottling, blistering and puckering of young developing leaves. Severely affected plants are stunted, pale and sickly. Mosaic affected leaves do not cure properly and have no market value.

Control Measures: 1. The most important control measure is adotpion of strict sanitary measures to prevent infection in nursery as well as in the field.
2. Wash hands with soap and running water before weeding or handling the seedlings.
3. One should not smoke or chew tobacco white working in the nursery.
4. Diseased seedlings should be removed and destroyed. Only healthy seedlings should be transplanted.
5. Spray 1.0% tannic acid in the early stages to check the disease
6. Use resistant varieties.

Root-Knot

It is a disease caused by nematodes. It attacks in nursery as well as in the fields. Attacked plants show knots or galls on the roots; leaves turn yellow and show poor growth; plants may wilt and die.

Control Measures: (1) Rabbing the beds with paddy husk in 15-20 centimetre thick layer.
(2) Keep the nurseries and fields clean of weeds.
(3) Deep ploughing in summer to expose eggs and larvae.
(4) Crop rotation with crops like groundnut, cotton, sesamum or chillies helps in reducing nematode build up in the soil.
(5) Application of Phorate at the rate of 15 kg per hectare in soil is helpful. Soil fumigation with methyl bromide or durofume at the rate of 15-18 ml/m* two weeks before sowing is quite effective.