Etiology and control of the following Grapes diseases: Downy mildew, Powdery mildew

Downy Mildew of Grapes:-

Pathogen:- Plasmopara viticola

Symptoms:-

> Irregular, yellowish, translucent sports on the upper surface of the leaves.

> Correspondingly on the lower surface, white, powdery growth on leaves.

> Affected leaves become, yellow, brown and gets dried.

> Premature defoliation.

> Dwarfing of tender shoots.

> Brown, sunken lesions on the stem.

> White growth of fungus on berries which subsequently becomes leathery and shrivels.

> Later infection of berries result in soft rot symptoms.

> No cracking of the skin of the berries.

> Spread:- Through sporangia by wind, rain etc.

> Survival:- As oospores present in the infected leaves, shoots and berries. Also as dormant mycelium in infected twigs.

> Optimum temperature:- 20-22°C

> Relative humidity:- 80-100 per cent

Management:- Spray Bordeaux mixture 1 % or Metalaxyl + Mancozeb 0.4 %.

Powdery Mildew of Grapes:-

Pathogen:- Uncinula necator

Symptoms:-

> Powdery growth mostly on the upper surface of the leaves.

> Malformation and discolouration of affected leaves.

> Discolouration of stem to dark brown.

> Floral infection results in shedding of flowers and poor fruit set.

> Early berry infection results in shedding of affected berries.

> Powdery growth is visible on older berries and the infection results in the

> Cracking of skin of the berries.

> It spread through air-borne conidia

> Through dormont mycelium and conidia present in the infected shoots and buds.

> Sultry warm conditions with dull cloudy weather, highly favourable.

Management:- Spray Inorganic sulphur 0.25 % or Chinomethionate 0.1 % or Dinocap 0.05 %.