POWDERY MILDEW (Erysiphe cichoracearum)
Symptoms: Powdery mycelial growth with whitish gray colour occurs on lower and upper surface of the leaves. The disease spreads when warm condition prevails.
Epidemiology: Dry and warm weather favours disease development.
Management : The disease is managed by spraying Wettable Sulphur (0.3%), Tridemorph (0.1 %), Dinocap(O.l %), Hexaconazole (0.05%), Fenarimol (0.025%), Propiconazole (0.025%) or Difenoconazole (0.06%) or Flusilazole (0.03 %) or Myclobutanil (0.1 %) three to four times at 15 days intervals.
CERCOSPORA LEAF SPOT (Cercospora malayensis and C. ablemoschi):
Symptoms: Cercospora malayensis induces brown and irregular spots while C. ablemoschi causes sooty black irregular spots. Under the humid conditions, both leaf spots cause severe defoliation. The fungus survives on crop residues in the soil.
Management : The disease can be effectively managed by spraying Mancozeb (0.2 %) or Zineb(0.2%) or Carbendazim (0.1 %).
OKRA YELLOW-VEIN MOSAIC DISEASE (Okra Yellow vein mosaic virus)
Symptoms: The disease is characterized by a homogenous interwoven net work of yellow veins enclosing islands of green tissue within. In severe cases, the infected leaves totally become yellow or plae colour. Infected plants remain stunted. Fuits from infected plants are more often malformed, small, pale in color and could be tough in texture. It is a Geminivirus belonging to Begomovirus genus of Geminiviridae. It is a single-stranded DNA virus. Yield losses due to OYVMV vary from 94 to 96% in different areas.
Epidemiology: It is transmitted in nature by the whitefly (Bemisia tabaci). The virus mainly perpetuates on weed hosts. Warm and dry weather favours 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. In addition to Okra, the virus also infects several species of Hibiscus, cotton and Abelmoschus
Management:
Cultural control
1. Eradication of early-infected plants and weed hosts from the field.
2. Border-cropping with maize, jowar or bajra, with insecticide sprays, give reduction of disease severity.
Chemical control
1. Soil-application of Furadon @ 1.5 Kg ai / ha at sowing.
2. Foliar spray of Acephate (0.15%) followed by spraying of Imidacloprid (0.3%) or Monocrotophos (0.05%) or Metasystox (0.05%) or Dimethoate (0.05%) is effective.
3. Chemical spray, followed by neem seed kernel extract (2%) is also effective, in rotation with insecticides.
4. Cultivation of resistant cultivars like Arka Anamika, Parbhani Kranthi, Varsha Uphar, VR06 and Punjab Kesari.
OKRA ENATION LEAF CURL DISEASE
Symptoms: Initial symptoms of the disease are small, pin-head enations on leaves. Warty and rough textured leaves follow this. Later still, the leaves begin to curl in adaxial direction. The most characteristic symptom of the disease is twisting of the main stem and lateral branches, along with enation. Infected plants produce small, deformed fruits. The pathogen is a single-stranded DNA virus. This virus causes considerable yield-loss ranging from 20 to 70 per cent, depending upon the stage of crop-susceptibility.
Epidemiology: The virus is a Gemini virus naturally transmitted by White flies (Bemisia tabaci). In summer months, higher incidence of the diseases is seen. Warm weather with low humidity favors multiplication and spread of the disease. In addition to Okra, the virus also infects other Malvaceous hosts such as hibiscus, cotton and Abelmoschu sps.
Management
1. Eradication of early-infected plants and weed ¬hosts from the field.
2. Border-cropping with maize, jowar, or bajra with insecticide sprays reduce incidence of disease.
3. Soil-application of Furadon @ 1.5 Kg ai/ha at the time of sowing.
4. Foliar spray of Acephate (0.15 %), followed by spray of Imadacloprid (0.03 %%) or Monocrotophos (0.05%) or Metasystox (0.05%) or Dimethoate (0.05%), is effective.
5. Chemical spray, followed by neem seed kernel extract (2%) is also effective, in rotation with insecticides.
OKRA FRUIT-DISTORTION MOSAIC DISEASE (Tobacco streak virus)
Symptoms: Chlorotic spots, chlorotic leaf blotches, distortion of
leaves, chlorotic streaking, distortion of fruits,
and severe yield losses. It 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. Yield losses due to this virus vary from 15 to 76 per cent, depending upon the stage of infection.
The disease is caused by a virus that is transmitted through pollen and by thrips. Many crops (such as soybean, sunflower, marigold) and weeds (such as Xanthium and 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 incidence of the disease.
3. Soil-application of Furadon @ 1.5 Kg ai/ha atthe time of sowing.
4. Foliar Spray of Acephate (0.15 %), followed by spray of Imadacloprid (0.03 %) or Monocrotophos (0.05%) or Metasystox (0.05%) or Dimethoate (0.05%), is effective.
5. Chemical spray, followed by neem seed kernel extract (2%) is also effective, in rotation with insecticides.