Temperate Vegetables

DISEASES

Fungal Diseases

Leaf blight or Alternaria blight : (Alternaria radicina and Alternaria dauci)

• It is predominant in winters.
• On the foliage, small dark brown to black spots with yellow edges appear at first mostly along the leaf margin.
• The number of spots gradually increases and the interveinal tissues die.
• In moist weather the blackening and shriveling progress so rapidly that entire field resembles frost injury.
• Disease is seed borne.

Control measures:

• Crop rotation should be adopted.
• Seed treatment with captan or thiram @ 3g/kg of seed before sowing will be helpful.
• Later on spray mancozeb (0.25%) at an interval of 7-10days.

Leaf spot or Cercospora blight : (Cercospora carotae)

• It is a wide spread disease of carrot.
• Symptoms appear first as elongated lesions along the edge of leaf segment, resulting in a lateral curling.
• In dry weather, the spots are light tan in colour whereas in humid weather the spots are darker in colour.

Control measures:

• Dipping seeds in 0.1 per cent carbendazim solution for 5 minutes is suggested.
• Crop rotation and sanitation are necessary.
• Spray with copper fungicides or Zineb@ 0.25-0.3per cent as and when the attack is noticed.

Powdery mildew : (Erysiphe spp.)

• It appears first on leaves, but later may spread on flowers, stem and fruits.
• Symptoms first appear as faint, slightly discoloured and tiny checkers from which white powdery spots spread to form various sized areas.

Control measures:

• Before observing symptoms, spray dinocap (0.05%) or wettable sulphur (0.2%) at 10-15 days interval.
• Sulphur dust is most effective. It is applied even after the appearance of the disease as this fungicide is both eradicative and protective.

Viral Diseases

Carrot Yellows:

• First appear on leaves which become yellow sometimes accompanied by vein clearing.
• Dormant buds in the crown grow out into chlorotic shoots which give a ‘witches broom' appearance on the tops.
• Older leaves are reddish, twisted and may eventually break off.
• The disease is transmitted by six spotted leaf hopper (Macrosteles divisus).

Control measures:

• Spray insecticides to control the hopper e.g. Dimethoate (0.05%) or Carbaryl (0.15%).

Root Diseases:

Watery soft rot: (Sclerotinia sclertiorum)

• Infected roots become soft and watery and white mycelium with black sclerotia is formed.

Gray mold rot: (Botrytis cinerea)

• The affected tissue is water soaked and light brown and later become spongy.
• Gray mold appear in moist atmosphere.

Black rot: ( Alternaria radicina)

• It is a wide spread disease.
• Foliage symptoms are just like those caused by Alternaria blight.
• On roots, black sunken areas irregular to circular in outline may develop.

Control measures of root diseases:

• Store roots at 0-2^oC to keep storage decay at a minimum level.

Bacterial Diseases

Bacterial soft rot : (Erwinia carotovora pv. carotovora)

• The infected tissue softens, becomes watery or slimy and as the rot progress the watery extrusion becomes more evident.
• A foul odour from decayed roots distinguishes it from the soft rot.

Control measures:

• Careful handling of roots during harvesting, grading or transit so that all bruises on root surface can be avoided.