Diseases of Fruit Plantation Medicinal and Aromatic Crops

Powdery mildew of grapes

Causal Organism: Uncinula necator


• Powdery mildew is an endemic disease wherever grapes 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 Maharashtra, Gujarat, Andhra Pradesh, Karnataka and Tamil Nadu.
• Economic Importance
• The disease causes extensive damage in whole of Europe and western USA, sometimes destroying the crop completely. French grapevine industry also suffered huge losses due to the epidemics of this disease during 1850-55.The disease not only reduces the yield and lower the fruit quality but wine prepared from infected fruits often develops off-flavor (Ough and Berg, 1979).

Symptoms


• The fungus attacks all the green parts of the plant at all stages of plant growth.
• It produces white to greyish powdery patches on the affected plant parts, including fruits, but young leaves are most susceptible and develop small whitish patches both on the upper as well as lower surface.
• These patches grow in size and coalesce to cover large areas on the leaf lamina and gets twisted. Malformation and discoloration of the infected leaves are also common symptoms, resulting in distortion.
• Similarly, powdery patches are also produced on the stem, tendril, flowers and young fruit branches.
• Diseased vines appear wilted and 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 which do not develop further and ripe.
• When blossom is infected, flowers may drop. Affected berries become malformed with cracks in the skin causing pulp expose.




Etiology


• Mycelia septate, thin, haustoria sub - epidermal, obligate parasite.
• Asexual spores are the barrel shaped conidia or oidia borne on oidiophore in chains. Sexual spores: Ascospores born inside Ascus in the ascocarp, which is called as Cleistothecium.

Mode of Spread and Survival


• It survives as dormant mycelia, as Cleistothecia on the shoots and buds of host plants from season to season.
• The disease spreads by the air- borne conidia/oidia.

Epidemiology


• The disease occurs in severe form from Oct- Nov in North India and Feb- June in South India.
• Disease is favoured by warm sultry weather and unfavoured in sunshine.
• Warm winter temperature from (20 to 33.5⁰C) has been found to be the cause for epidemics in Hyderabad.
• Disease development is adversely affected by rains.

Life cycle



Management


Cultural practices

• The use of training systems which allow proper air circulation through the canopy and prevent excess shading helps in reducing the disease incidence.
• Orchard sanitation is also important in reducing disease pressure during the growing season.

Chemical control

• Fungicides like Sulphur, Dinocap, Benomyl, Triadimefon, Penconazole, Mycobutanil and Flusilazole (%) are used commercially although not as extensively as sulphur, to control the disease.
• Use of fungicides for controlling powdery mildew should begin during early stages of vine development. Spray schedule at an interval of 7-10 days is usually required for effective control by sulphur.
• Dinocap is to be sprayed at an interval of 10-14 days, while sterol biosynthesis inhibiting fungicides are commonly used at 14-21 days schedule.
• For effective control, fungicid spray should start just after bud burst.
• The fungicides should be sprayed alternatively and the same fungicide should not be sprayed repeatedly