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Pl. Path. -508(Diseases of Vegetables and Spices Crops) SUBMITTED BY: Dinesh Dalvaniya Reg.no:04-00876-2011 M.sc.(Agri.) 2nd Sem Ag. Entomology
DISEASES OF OKRA5.Yellow vein mosaic7. Root-knot9.Wilt11.Cercospora leaf spot13.Powdery mildew
1. Yellow Vein Mosaic C.O.:- Virus (Yellow Vein Mosaic virus) Transmission: By vector – White fly Symptoms Yellowing of the entire network of veins in the leaf blade is the characteristic symptom. In severe infections the younger leaves turn yellow, become reduced in size and the plant is highly stunted. In a field, most of the plants may be diseased and the infection may start at any stage of plant growth. Infection restricts flowering and fruits, if formed, may be smaller and harder.
• Diseases cycle Diseases Secondary inoculum Host • through vectors SeasonFavorable condition Off season Primary inoculum • wild hostsTemp. > 32-40 0C,Less relative Humidity ( < 60 % )
Control• The virus is transmitted by the whitefly (Bemisia tabaci), So control of this pest will gives better results.• Parbhani Kranti, Janardhan, Haritha, Arka Anamika and Arka Abhay can tolerate yellow vein mosaic.• Spraying monocrotophos 1.5 ml/litre of water can restrict the disease spread.• It can be controlled by application of Chlorpyriphos 2.5 ml + neem oil 2 ml/lit of water.
2 Root Knot C.O.:-Meloidogyne incognita & Meloidogyne javanica Symptoms• Above ground symptoms:• Plant shows unthrifty development and stunted growth.• The leaves are yellowish green to yellow and tend to dropping and then there will be a wilting.• Below ground symptoms:• The most characteristics symptoms of the disease is the formation of knots or galls on the root .
The main root and laterals bear spherical to elongated various size of galls. In some cases the plants would show chlorosis but rarely do the plants die from nematode infection. Disease cycle: Each female lays approximately 500 eggs in a gelatinous matrix produced by female. First and second stage juveniles (Larvae ) are worm like and develop inside each egg. The second stage juvenile emerges from egg into the soil. The nematode than enter under third and forth moult. Fourth stage continues to grow in thickness and become adult female, which appear pears like shape.
Favourable conditions :-• Egg larvae develop in 16 days at 270C temperature and 80 days at 140C temperature.• Nematode female favours 25-280C.• Sandy light soils favours their movement.• High temp. such as 40-500C kill these larvae quickly.• In general, the temperature of 25-280C are best for infection, rapid multiplication and increased size of galls.
Control• Follow crop rotation and elimination of weed host.• The addition of non-edible oil cakes like castor cake/ mustard cakes @2.5 t/ha.• Summer deep ploughed• Flooding is effective to minimize the disease.• Soil solarization with 100 gauge (25µm) LLDP plastic covering during April-May for 15 days.• Soil application of carbofuran (3G) @33kg/ha or phorate (10 G) @ 10 kg/ha in furrow.
3. Wilt Of Okra : C.O.:- Fusarium vasinfectum Symptoms The conspicuous symptom is a typical wilt, beginning with a yellowing and stunting of the plant, followed by wilting and rolling of the leaves as if the roots were unable to supply sufficient water. Finally, the plant dies. If a diseased stem is split lengthwise, the vascular bundles appear as dark streaks. When severely infected, nearly the whole stem is blackend. The fungus has mostly three-septate spores.
• Diseases cycle Diseases Secondary inoculum Host • Through water • Irrigation rain SeasonFavorable condition Off season Primary inoculum • Soil borne Temperature range of • Diseased plants 54 to 100°F, with the optimum at 77°F.
Control• A better plan is to use a 6-year rotation before the fungus is destructive; this permits many years of okra growing without too much loss.• Drench the field with Copper oxychloride @3g/litre of water.• Treat the seeds with Carbandazim or Mancozeb @ 3g/kg seed.• Grow resistant varieties like Pusa Makhamali, Okra I.S. 9273, 9857, C.S. 3232, 8899, I.S. 6653, 7194 and Pusa Sawani.
4. Cercospora Leaf Spot C.O.:- Cercospora malayensis & C. abelmoschi Symptoms• In India, two species of Cercospora produce leaf spots in bhendi.• C. Malayensis causes brown, irregular spots and C. abelmoschi causes sooty black, angular spots.• Both the leaf spots cause severe defoliation and are common during humid seasons.• The fungi survive through conidia and stomata on crop residue in soil.
• Diseases cycle Diseases Secondary inoculum Host • air borne conidia SeasonFavorable condition Off season Primary inoculum • plant debris•High humidity • Infected plants•Low temperature•More application of N&P
Control• Spraying Mancozeb or Zineb 2 g or Carbendazim 1 g/ litre can control the disease.• They can be controlled by spraying Bordeaux mixture (1 per cent) or Diathane M-45 (0.2 per cent), starting from about a month after sowing and repeating at fortnightly interval, depending upon the severity of the disease incidence.
5. Powdery Mildew : C.O.:- Erysiphe cichoracearum Symptoms• Powdery mildew is very severe on bhendi.• Greyish powdery growth occurs on the under as well as on the upper surface of the leaf causing severe reduction in fruit yield.
Control• The disease is effectively controlled by dusting finely ground sulphur at 30 kg/ha or spraying wettable sulphur 3 g/litre of water or Dinocarp 1 ml/litre of water three to four times at 15 days intervals.• Karathane (0.03 per cent) and Bavistin (0.2 per cent) are also effective.