Pl. Path. -508

(Diseases of Vegetables and Spices Crops)

SUBMITTED BY:

Dinesh Dalvaniya

Reg.no:04-00876-2011

M.sc.(Agri.) 2nd SemAg. Entomology

DISEASES OF OKRA

1.Yellow vein mosaic

2. Root-knot

3.Wilt

4.Cercospora leaf spot

5.Powdery mildew

1. Yellow Vein Mosaic C.O.:- Virus (Yellow Vein Mosaic virus) Transmission: By vector – White fly SymptomsYellowing 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

Favorable condition

Temp. > 32-40 0C, Less relative Humidity ( < 60 % )

Primary inoculum• wild hosts

Season

Off season

Host Secondary inoculum• through vectors

Diseases

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 KnotC.O.:-Meloidogyne incognita & Meloidogyne javanicaSymptoms

• 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

Favorable condition Temperature range of 54 to 100°F, with the optimum at 77°F.

Primary inoculum• Soil borne• Diseased plants

Season

Off season

Host Secondary inoculum• Through water• Irrigation rain

Diseases

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 SpotC.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

Favorable condition

•High humidity•Low temperature•More application of N & P

Primary inoculum• plant debris• Infected plants

Season

Off season

Host Secondary inoculum• air borne conidia

Diseases

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.

• Diseases cycle

Favorable condition

•Temp. 28 oC,• Dry weather condition (< 60 % RH) •cloudy weather favours the disease development.

Primary inoculum• plant debris

Season

Off season

Host Secondary inoculum• air borne conidia

Diseases

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.