The following points highlight the four major vectors borne problems in vegetable crops. The vector borne problems are: 1. Whitefly Transmitted Virus Diseases 2. Aphid Borne Virus Diseases 3. Thrips Transmitted Virus Diseases 4. Other Diseases.
Contents
Vegetable Crop: Vector Borne Problem # 1. Whitefly Transmitted Virus Diseases:
i. Tomato Leaf Curl Disease:
Severe stunting of the plants with downward rolling and crinkling of the leaves characterize leaf curl disease. The newly emerging leaves exhibit slight yellow coloration and later on they also show curling. Older leaves become leathery and brittle.
The nodes and Internodes are significantly reduced in size. The infected plants look pale and produce more lateral branches giving a bushy appearance. The fruits from infected plants are small and deformed. Losses due to this disease range from 30-92.5% depending on the stage of infection and cultivar’s type.
Epidemiology and Spread:
Tomato leaf curl diseases is caused by Tomato Leaf Curl Bangalore virus (ToLCBV), Tomato leaf curl Karnataka virus (ToLCKV), Tomato Leaf Curl New Delhi virus (ToLCNDV), Tomato leaf curl joydevpur virus (ToLCJV), Tomato leaf curl palampur virus (ToLCPaV) and Tomato Leaf Curl Gujarat virus (ToLCGV) which are transmitted by Whiteflies (Bemisia tabaci) in nature.
High temperature and Low humidity favors disease incidence and vector population build up. The virus also infects and survives on alternate crops and on weed hosts like Acanthospermum hispidum, Abutilon variegata, Euphorbia geniculata, Solarium, nigrum, Xanthium strumarium, Tobacco, Sun Hemp, Parthenium and Zinnia elegans.
Management Strategies:
(а) Nursery Stage:
1. Growing of nursery under Nylon net cover (60-80) mesh.
2. Application of systemic Insecticides like Furadon at the rate 1.0 Kg ai / ha at the time of sowing seeds in the nursery bed.
3. Prior to transplantation the seedlings should be sprayed with Acephate at the rate 1.5 g per liter or Monocrotophos (0.05%).
(b) Main Field Management:
1. Sowing of border crops like Maize, Bajra/Jowar 10-15 days before the transplanting of Tomato.
2. Mulching with silver or black colored mulches on tomato fields.
3. Soil Application of Furadon at the rate 1.5 Kg ai/ha in the field along with a basal dose of fertilizers at the time of tomato seedling transplanting.
4. Roughing of leaf curl infected plants and weeds as soon as the symptoms are expressed.
5. Spraying of insecticides like Monocrotophos (0.05%), Acephate at the rate 1.5 g per liter or Hostothion 1.0 ml/liter.
6. Cultivation of Tomato Cultivars resistant/tolerant such as Avinash, Mruthinjayl, aksmi etc.
ii. Chilli Leaf Curl Disease (Chilli Leaf Curl Virus, Begomovirus Genus of Geminiviridae):
Symptoms consists of upward and downward curling of leaves, leaf margins develop pale green to yellow color, which extends into the interveinal areas. The nodes and Internodes are significantly reduced in size.
The infected plants assume bushy appearance with severe stunted growth look pale and produce more lateral branches giving a bushy appearance. The fruits from infected plants are small and deformed. It is a single stranded DNA virus.
Epidemiology:
Field spread occurs due to whitefly insect vector (Bemisia tabaci). This disease increase with increase in temperature coupled with relative humidity. The virus mainly perpetuates on weed hosts. Warm and dry weather favors disease spread.
In southern India the disease epidemics will be more during March to June period where as in Northern Indian conditions epidemics will occur from June to October period.
Management:
Cultural Control:
1. Growing of nursery under Nylon net cover (60-80) mesh.
2. Eradication of early infected plants and weed hosts from the field.
3. Two rows of border cropping with Maize, Jowar, or Bajra give a reduction in the disease spread.
Chemical Control:
1. Soil Application of Furadon at the rate 1.5 kg ai/ha at the time of sowing.
2. Prior to transplantation the seedlings should be sprayed with Acephate 1.5 g/liter or Monocrotophos at the rate 1.5 ml per liter or Dimethoate at the rate 2.0 ml per liter.
3. Foliar Spray of Acephate at the rate 1.5 g per liter followed by Spraying of Imadacloprid at the rate 0.3 ml per liter are effective
4. Chemical spray followed by neem seed kernel extract at the rate 2% is also effective in rotation with insecticides.
iii. Okra Yellow Vein Mosaic Disease:
Yellow vein mosaic is a very serious disease of Okra in India. The infected plants get dwarfed and the leaves show a homogenous network of yellow veins enclosing islands of green tissues. Occasionally younger leaves appear completely chlorotic.
Most of the infected leaves show vein thickening at their lower sides. The fruits from the infected plants are more often malformed, small, pale in color and would be tough in texture.
Epidemiology and Spread of the Disease:
Yellow vein disease of Okra is caused by Yellow vein mosaic Gemini virus and is transmitted in nature by the whitefly (Bemisia tabaci). In addition to Okra, the virus also infects several species of Hibiscus, Cotton and Abelmoschus. The virus mainly perpetuates on weed hosts. Warm and dry weather favors disease spread.
Control:
Eradication of early infected plants and weed hosts from the field:
1. Border cropping with maize, Jowar, or Bajra with insecticide sprays give a reduction in the disease
2. Soil Application of Furadon at the rate 1.5 kg ai/ha at the time of sowing
3. Foliar Spray of Monocrotophos (0.05%) or Metasystox (0.05%) or Dimethoate (0.05%).
4. Cultivation of resistant cultivars like Arka Anamika, Parbani Kranthi, and Punjab Kesari.
iv. Okra Enation Leaf Curl Disease:
Initial symptoms of the disease are small pinhead enations on leaves. Warty and rough textured leaves follow this. Later on the leaves begin to curl in an adaxial direction. The most characteristic symptom of the disease is twisting of the main stem and lateral branches along with enations. The infected plants produce small-deformed fruits.
Epidemiology and Spread of the Disease:
The virus is a Geminivirus, which is naturally transmitted by Whiteflies (Bemisia tabaci). In summer months a higher incidence of the diseases is seen. Warm weather with low humidity favors the multiplication and spread of the disease.
Management Measures:
1. Roughing of early-infected plants as and when noticed.
2. Application of Furadon at the rate 1.5 kg ai/ha at the time of sowing
3. Spraying of Dimethoate (0.05%) or Monocrotophos (0.05%) or Neem oil (2%) at 10 day intervals.
v. Bean Yellow Mosaic Disease:
Bright yellow patches interspersed with green areas on the leaves, at later stages the yellow patches increase in size and cover the entire leaf, characterize this. Early infected plants will become stunted with a reduced fruit size and yield.
Epidemiology and Spread of the Disease:
Mungbean yellow mosaic virus causes yellow mosaic disease of beans; a begomovirus belongs to Geminiviridae family. The virus is transmitted in nature by White flies (Bemisia tabaci).
Management Measures:
1. Roughing of early-infected plants as and when noticed.
2. Application of Furadon at the rate 1.5 kg ai/ha at the time of sowing
3. Spraying of Dimethoate (0.05%) or Monocrotophos (0.05%) or Neem oil (2%) at 10 day intervals.
Vegetable Crop: Vector Borne Problem # 2. Aphid Borne Virus Diseases:
Non-persistent aphid transmitted viruses have been implicated as the major problems in Vegetable Crops. Measures that interfere with the landing behavior of the aphids or the transmission process to achieve some control should be developed.
The application of insecticides is of little use as alighting aphids transmit the virus before the insecticide kills them. However some of the methods are available which can reduce the incidence of aphid borne viruses.
i. Tomato Shoe String Disease:
The characteristic symptoms of this disease are initial mosaic and distortion of leaves, narrowing filiformity and rat-tail appearance of the leaf. The plats would be stunted and the fruits would be deformed and reduced in yield.
Epidemiology and Spread of the Disease:
This disease is caused by Cucumber Mosaic Virus (CMV), in nature it is transmitted by aphids Aphis gossypii, A. craccivora, and M. persicae) and also through seed. Other crops like chili, Cucumber and weed hosts serve as an alternate source of Inoculums for the spread of the virus by aphids.
ii. Chilli and Capsicum Mosaic Diseases:
The important symptoms of this disease are mottling, Distortion, and reduction in leaf lamina. Sometimes the infected plants show vein banding, yellowing, and leaf curling symptoms. Stunted growth and reduction in fruit yield and size in case of early infection is seen. In later stages of Infection the fruits become malformed and unfit for human consumption. Yellow and Green streaks may be produced on the fruits.
Epidemiology and Spread of the Disease:
Many viruses in chili and capsicum cause the mosaic symptoms and often more than one virus infect at the same time. The major ones are: Cucumber mosaic virus (CMV), Potato Virus Y (PVY), Chili Veinal Mosaic Virus (ChiVMV), Tobacco Mosaic Virus (TMV). Except TMV all other viruses are spread by different aphid species and through mechanically. The aphids transmit these viruses in a non-persistent manner.
Management Measures:
(а) Nursery Stage:
1. Growing of nursery under Nylon net cover (60-80) mesh.
2. Soil application of systemic Insecticides like Furadon at the rate 1.0 kg ai/ha at the time of sowing seeds in the nursery bed.
3. Prior to transplantation the seedlings should be sprayed with Acephate 1.5 g/liter or Monocrotophos at the rate 1.5 ml per liter or Dimethoate at the rate 2.0 ml per liter.
(b) Main Field:
1. Sowing of border crops like Maize, Bajra / Jowar 15 days before the transplanting of Tomato/Brinjal/Chilli/onion.
2. Removal of early-infected plants from the field.
3. Spraying of Acephate at the rate 1.5 g per liter at 7 to 10 days interval 15 days after transplanting until fruit formation (or) Spraying of Hostothion at the rate 1.0 ml per liter at 7 to 10 days interval 15 days after trans planting until fruit formation (or) Imdacloprid at the rate 0.5 ml per liter at 7 to 10 days interval 15 days after trans planting until fruit Formation (These chemicals should be alternated with one another and should not use one chemical continuously.
4. Spraying of Neem seed Kernel extract 2% + sticker 10 days interval 15 days after trans planting until fruit formation.
5. Mulching with silver or black polythene color mulch sheet.
6. Seed borne infection can be prevented by soaking of seed in 5% Calcium hypochlorite for 15 minutes or 10% Trisodium phosphate solution for 20 to 30 min and drying.
iii. Mosaic Diseased of Cucumber, Pumpkin, Musk Melon and Water Melon:
The viral diseases are similar in most of the cucurbit crops. This disease is characterized by mosaic mottling of the leaves. Distortion and blistering symptoms are very common on the leaves. The size of the leaf lamina gets reduced and in severe cases highly distorted. Fruits from infected plants are deformed, discolored and blistered.
Cause and Disease spread. A number of viruses cause mosaic symptoms in cucurbits. The major ones are Cucumber Mosaic virus (CMV), Papaya Ring Spot Virus W-strain (PRSV-W), and Cucumber Green Mottle Mosaic Tobamo virus (CGMMV).
CGMMV does not have any insect vector but it is spread by mechanical and seed transmission. Where as CMV and PRSV-W are spread in nature by different aphid species and are also transmitted by seed.
Control Measures:
1. Eradication of early-infected plants from the field.
2. Selection of seeds from absolutely virus free plants.
3. Use of silver or black coloured Polythene mulch.
4. Spraying of NSKE 4% alternated with Rogor (30 EC) 2 ml/Liter or Nuvacron (36 EC) 1.5 ml/Liter or Metasystox (25 EC) 2 ml/liter at 10 days interval starting from 15 day after planting.
iv. Cowpea Mosaic Disease:
Many viruses cause mosaic symptoms on cowpea but Cowpea aphid borne mosaic is very important. The infected leaves develop a typical mosaic of broad and raised dark green patches along with chlorotic streaks or spots. The leaves also show green vein banding and plants appear pale colored with a reduced growth and fruit yield.
Cause and Spread:
The disease is caused by Cowpea aphid borne mosaic virus (CABMV). Primary spread is by seed and secondary spread in the field is by aphids Aphis gossypii and Myzus persicae.
Control Measures:
1. Roughing of early infected plants and weed hosts from the field.
2. Use and selection of virus free seeds from un infected plants.
3. Application of Furadon at the rate 1.5 kg ai/ha at the time of sowing followed by a foliar spray of Monocrotophos (0.01%) or Dimecron 0.5 ml/liter at 10 day intervals.
v. Bean Common Mosaic Disease:
This is the most important disease of Beans in India. The symptoms are severe mosaic mottling of the leaves and various types of leaf malformations. Trifoliate leaves affected with mosaic usually have irregular shaped, light yellow and green areas of various sizes.
Sometimes infected leaves may be narrower than the normal ones. With down ward cupping caused by un equal growth of the tissue. Infected plants produce very few small and abnormal fruits.
Cause and Spread:
The disease is caused by Bean Common Mosaic Virus (BCMV) belonging to potyvirus genus of potyviridae family. BCMV is transmitted by seed and aphids in nature. Disease spread in the field is due to transmission by aphids and the primary source of infection is by seeds. The major aphid vectors include Aphis gossypii, A. craccivira, and M. persicae.
Control Measures.
1. Roughing of early infected plants and weed hosts from the field.
2. Use and selection of virus free seeds from un infected plants.
3. Application of Furadon at the rate 1.5 kg ai/ha at the time of sowing followed by a foliar spray of Monocrotophos (0.01%) or Dimecron 0.5 ml/liter at 10 day intervals.
Vegetable Crop: Vector Borne Problem # 3. Thrips Transmitted Virus Diseases:
Tospoviruses are transmitted by thrips, minute insects belonging to the order Thysanoptera. Thrips tend to occur in large population across broad hosts, geographic and climatic ranges. This makes them especially significant as direct crop pests and also as virus vectors.
The thrip management programmes are built upon a number of principles including:
1. The biology of the thrips on the crop and the damage caused including economic thresholds.
2. Spatial distribution within and between plants which determines the development of efficient sampling schemes.
3. The influence of host plant resistance on thrips biology.
4. Importance of the natural enemies in regulating thrips population.
5. The utility of chemical and physical control options.
6. The utility of Chemical control strategies.
Some of the thrips borne tospovirus problems are as follows:
i. Spotted Wilt Disease of Tomato:
This disease is characterized by bronzing of the young leaves, chlorosis followed by necrotic ring spots. Necrotic spots appear under the growing tips and the entire twig dies back. In some cases this leads to severe stunting and cessation of growth. Early infected plants have deformed uneven ripe fruits while the fruits formed after late infection show concentric rings.
Cause and Spread. Groundnut bud necrosis virus (GBNV) is naturally transmitted by thrips insect vector (Thrips palmi) in a persistent manner. Thrips can acquire the virus only during the larval stage and then become infective after metamorphosis into adults.
This virus is not transmitted through seed. It infects several crop plants such as Cowpea, mungbean, urdbean, Frenchbean, pea, groundnut, Potato, chilli, and brinjal in addition to several weed hosts.
Control Measures:
1. Raising of seedlings under Nylon nets (80 mesh).
2. Application of Furadon at the rate 1 kg ai/ha the nursery bed at the time of sowing.
3. Use of aluminum surfaced mulch dramatically reduces the thrips population and the virus incidence in tomato and pepper.
4. Application of Insecticides Acephate (2 g/Liter)/Imidacloprid (0.25%)/Acrinathin (0.1%).
5. Roughing of infected plants and weed hosts.
6. Crop rotation to avoid cultivation of susceptible crops in consecutive years.
ii. Watermelon Bud Necrosis Disease:
The disease symptoms include mild mottling, crinkling, yellowing of growing tips. Later necrotic spots appear, rugosity of young leaves and narrowing of plant lamina is also seen. Plants get severely stunted with shortened internodes and become very brittle. Upright growth of young branches, Unopening of flower buds.
Bud necrosis and die back are the major symptoms of this disease another conspicuous symptom is the presence of longitudinal brown necrotic streaks on the vines , tendrils petioles and fruit stalk. As the disease progresses the stems get split and start drying from the tip. Fruit set and yield get drastically reduced.
Cause and Spread:
The disease is caused by Watermelon Bud Necrosis virus (WBNV). It is transmitted by melon thrips Thrips palmi. Many weeds like Cassia tora, Emilia and crop plants like musk melon, cucumber also serve as alternate hosts to both the virus and the vector.
Control Strategies:
1. Raising of seedlings under Nylon nets (80 mesh).
2. Application of Furadon at the rate 1 kg ai/ha the nursery bed at the time of sowing.
3. Use of aluminum surfaced mulch dramatically reduces the thrips population and the virus incidence in tomato and pepper.
4. Application of Insecticides Acephate (2 g/Liter)/Imidacloprid (0.25%)/Acrinathin (0.1%).
5. Roughing of infected plants and weed hosts.
6. Crop rotation to avoid cultivation of susceptible crops in consecutive years.
Vegetable Crop: Vector Borne Problem # 4. Other Diseases:
i. Okra Fruit Distortion Mosaic Disease (Tobacco Streak Virus):
Symptoms:
This disease is of recent origin produces bright yellow patches interspersed with green areas on the leaves, at later stages the yellow patches increase in size and leaf deformation occurs. The fruits are highly distorted and unmarketable. The yield losses due to this virus varied from 15 to 76% in depending upon stage of infection.
Epidemiology:
This disease is caused by which is transmitted through pollen and thrisps. Many crops such as Soybean, Sunflower, Marigold and weeds such as Xanthium, parthenium act as reservoir hosts of this virus.
Management:
1. Eradication of early infected plants and weed hosts from the field.
2. Border cropping with maize, Jowar, or Bajra with insecticide sprays give a reduction in the disease.
3. Soil Application of Furadon at the rate 1.5 kg ai/ha at the time of sowing.
4. Foliar Spray of Acephate at the rate 1.5 g per liter followed by Spraying of Imadacloprid at the rate 0.3 ml per liter or Monocrotophos (0.05%) or Metasystox (0.05%) or Dimethoate (0.05%) is effective.
5. Chemical spray followed by neem seed kernel extract at the rate 2% is also effective in rotation with insecticides.
ii. Tomato Big Bud Disease (Tomato bigbud Phytoplasma):
This disease is characters by transformation of flower buds into green color and phyllody of floral parts, proliferation of axillary buds and reduction in leaf size. The calyx gets enlarged and forms a bladder like structure with a toothed opening at the tip giving the appearance of a big bud. The diseases plants normally do not produce fruits but in rare cases a few distorted fruits form.
Epidemiology:
Tomato big disease is caused by Tomato big bud Phytoplasma that is transmitted by the leafhopper Orosius argentatus. The insect breeds and feeds on infected weed hosts and only migrates into tomato when the weeds become undesirable.
Management:
1. Destruction of weed hosts on the borders of the tomato crop.
2. Removal of early infected plants and destruction.
3. Spraying of insecticides to control leaf hoppers.
iii. Tomato Bunchy Top Disease (Potato spindle tuber viroid and Tomato bunchy top viroid):
Total cessations of growth of terminal branches and close crowding of the foliage, which leads to bunchy appearance. Usually produce few fruits, which are very small in size. Both the virods are single stranded RNA.
Epidemiology:
The diseases usually spread in the cooler part of the season when temperature is 20 to 25°C. Primary source of inoculums is from infected seed. In field cultural operations will spread from plant to plant.
Management:
1. Selection of healthy disease free seed/seedlings.
2. Removal of early-infected plants and destruction.