Diseases of Bhindi
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Diseases of Bhindi
- 1. Diseases of Okra/Bhindi HPP 5311 3(2+1) Disease of vegetable, ornamental and spice crops
- 2. FUSARIUM WILT • The disease can appear on any stage of plant growth and the crops planted during summer months suffer more than the crops planted during February-March.
- 3. Symptoms • The characteristic symptoms of the disease appear as yellowing and stunting of the plants followed by wilting and rolling of the leaves and finally the plant dies. • Before the appearance of typical wilting symptoms, the leaves hang down during daytime and recover again in the night but ultimately they wilt and die. • Vascular bundles of the affected plants appear as dark streaks and the whole stem is blackened in case of severe infection.
- 5. Pathogen • Fusarium oxysporum f.sp. vasinfectum (Atkinson) Snyder and Hansen. • The mycelium is hyaline and intracellular in the host. • Macroconidia are mostly 3 septate and microconidia are 0 to 1 septate. • Macroconidia are fusiform, falcate, curved and formed on sporodochia and pionnotes. In mass these conidia appear buff to salmon orange in colour. • The microconidia are 5-12 x 2-3.5 μm while macroconidia are 40-50 x 3-4.5 μm in size. • Both intercalary and terminal chlamydospores are formed which are broadly ovate.
- 6. Disease cycle and epidemiology • The fungus survives from one season to other in the form of chlamydospores and in infected seeds. • In contact with the host roots, the chlamydospores or conidia germinate and penetrate. • The pathogen proliferates extensively in the cortical tissues, extending up and down. • After some growth in root cortex, the pathogen reaches the xylem vessels where it multiplies very rapidly and result in browning of xylem vessels and clogged at further places. • The optimum temperature for growth of the fungus is 25⁰C and for disease development ranges between 22 – 28⁰C. • Moisture is not that much important for infection.
- 7. Management • Cultural practices like long crop rotations, exposing the soil to the sun during summer months by deep ploughing, soil solarization and destruction of diseased roots are some of the practices which can reduce the disease. • Some varieties of okra like Pusa Sawani and Pusa Makhmali have been reported resistant to this disease. • Use healthy seed and treat with carbendazim (0.2%).
- 8. CERCOSPORA LEAF SPOT Symptoms • Three different species of Cercospora are associated with this disease. The symptoms of each species are described below: Cercospora abelmoschi: • The fungus produces indefinite leaf spots but grows as a sooty mould on the lower surface of the leaves. • Severely affected leaves roll, wilt and fall down to the ground.
- 9. Cercospora hibiscina: • The fungus produces dark olivaceous patches of mould on the lower surface of the leaves. Cercospora malayensis: • The spots caused by this species produce definite leaf spots with grey centers and red to purple borders.
- 10. Pathogen(s) • In C. abelmoschi, the conidiophores are long, brown and bear pale olivaceous, slightly tapered conidia. • The conidiophores of C. hibiscina are extremely long sometimes up to 1000 μm in size, narrow and bear conidia that are sometimes hyaline and appreciably more narrow then those of C. abelmoschi. • The conidiophores of C. malayensis are borne in clusters of 5-20 and bear conidia, which are colourless, narrow, long, and tapering from the blunt base to the sharp tip.
- 11. Disease cycle and epidemiology • The three species cause infection in moderate temperatures (25-29 ⁰C) and high humidity.
- 12. Management • Cultural practices like collection and destruction of infected plant debris, crop rotation and destruction of wild hosts from in and around the field should be followed to keep the disease under check. • With the initiation of the disease, spray the crop with fungicides like carbendazim (0.1%) or benomyl (0.1%) or mancozeb (0.25%) or chlorothalonil (0.2%) and repeat at 10 to 14 days interval.
- 13. Powdery mildew • Powdery mildew is an important disease of this crop and under favourable weather condition causes significant yield reductions particularly if the infection takes place at in early stages of plant growth
- 14. Symptom • Symptoms first appear as minute discoloured patches with thin fine network of white mycelium arising at many places on the upper surface of lower leaves. • These white patches soon join together to form larger white greyish powdery coating discernible on the severely affected leaves and in later stages the affected leaves turn yellow and finally drop.
- 15. Pathogen Erysiphe cichoracearum . • The conidia are single celled, hyaline, barrel-shaped and in long chains. • The conidial dimensions vary with the physiologic race and the host. • Cleistothecia are globose, dark with hyaline to dark brown and mycelioid appendages. • They contain 8 to 18 asci and the asci are pedicellate, ovate to broadly ovate or ellipsoid. • The number of ascospores per ascus is usually two, rarely three. The ascospores are one celled and hyaline oval to sub-cylindrical.
- 16. Disease cycle and epidemiology • The pathogen requires 60-80 per cent relative humidity for the development of the disease and dry conditions for the growth and sporulation of the fungus
- 17. Management Cultural control: • Monitor the adjacent field for infection • Maintain proper plant spacing for reducing the relative humidity Biological control: • Spray azadirachtin 0.3% (300 ppm) neem oil based EC @ 800-1000 ml in 200 l of water/acre Chemical control: • Spray sulphur 80% WP @ 1252 g in 300-400 l of water/acre or dinocap 48% EC @ 90 ml in 300 l of water/acre •
- 19. • The characteristic symptoms include vein yellowing and thickening of leaves forming a net work of veins and veinlets in the infected leaves. • Initially the leaves exhibit only yellow coloured veins but under severe infection, the leaves become completely chlorotic and turn yellow. • The chlorophyll content of the leaves is reduced. Infected plants produce very few small sized leaves, deformed and give a stunted look. • Affected plants produce very few small sized pale fruits.
- 20. Virus • The disease is caused by Yellow Vein Mosaic Virus (YVMV) and belongs to the Begomovirus. • The size of virus is 18 x 30 nm. • Virus particles are spherical, isometric measuring 28-30 nm.
- 21. Disease cycle and epidemiology • Virus is not sap transmissible but under artificial conditions, it can be transmitted by grafting. • In nature, virus is transmitted by white fly Bemisia tabaci. in a persistent manner. • Both wild and cultivated plants serve as the source of inoculum and the incidence of the disease in a particular area depends upon the prevalence of wild or cultivated host plants, population buildup of the vectors and environmental conditions. • Dry hot weather with little or no rainfall was conducive for disease development and also for the multiplication of the vector population
- 22. Management • Various cultural practices like destruction of wild hosts from in and around the field, avoidance of mixed cropping of pumpkin, adjustment of date of sowing to avoid the period of maximum population of the whiteflies and regular removal of affected plants upto 55 days help in reducing the incidence of the disease. • Application of yellow coloured polythene mulch significantly delays the appearance of the disease. • Peppermint plants act as repellent for whitefly. • Use resistant cultivars like Punjab Padmini, Punjab-8, Prabhani Kranti and Hissar Unnat. • Four sprays of Metasystox (demeton-S-methyl) at 15, 30, 45 and 60 days after sowing have been reported effective in controlling the insect vectors and keeping the disease under check.