Powdery mildew

Powdery mildew
    Causal organism- Erysiphe polygoni DC.
      • Powdery mildew is an endemic disease wherever the opium are grown in the world. The disease has been reported from the American continent, Europe, Africa, Australia and Asia.In India, the disease is most common in North India.
    Symptoms
    • The fungus attacks all the green plant parts at all stages of plant growth.
    • The fungus produces white to grayish powdery patches on the affected plant parts including fruits but young leaves are most susceptible and develop small whitish patches both on upper as well as lower surface.
    • These patches grow in size and coalesce to cover large areas on the leaf lamina. Malformation and discoloration of the affected leaves are also common symptom, resulting in distortion.
    • Similarly, powdery patches are produced on the stem, tendril, flowers and young fruit branches.
    • Diseased vines appear wilted and the stem portion turns brown.
    • The infected blossom and berries turn dark in colour, irregular in shape and brittle.
    • In advance stage of infection, berries may develop cracks and such berries do not develop and ripe.
    Etiology: Erysiphe polygoni
    • Mycelia is septate, external thin mycelia, haustoria is sub epidermal, obligate parasite.
    • Asexual spores are barrel shape conidia borne on oidiophore in chains asexual fruiting body oidia.
    • Sexual spores are ascospores inside the Ascus in the ascocarp Cleistothecium.
    Mode of survival
    • Primary source of inoculum :Ascospores, Dormant mycelia.
    • Secondary source of inoculum: oidia
    • It survives as dormant mycelia and as Cleistothecia on the shoots and buds from season to season.
    • The disease spreads by the air- borne conidia.
    Epidemiology
    • The disease occurs in severe from Oct- Nov in North India and Feb- June in South India.
    • Disease is favoured by warm sultry weather and retarded by sunshine.
    • Warm winter temperature from 20 to 33.50C has been found to be the cause for epidemic in Hyderabad.
    • Disease development is adversely affected by rain.
    Life cycle

    Management
    Cultural practices
    • The proper air circulation through the canopy and prevent excess shading help in reducing the disease.
    • Orchard sanitation is also important in reducing the disease pressure during the growing season.
    Chemical control
    • Fungicides like sulphur, dinocap, benomyl, are used commercially although not as extensively as sulphur, to control the disease.
    • The use of fungicides for control of powdery mildew should begin during early stages of development. Spray schedules of 7-10 days are usually required for effective control by sulphur.
    • Dinocap has 10-14 days schedule while; sterol biosynthesis inhibiting fungicides are commonly used at 14-21 days schedule.

Last modified: Saturday, 23 June 2012, 4:25 AM