📈 Diseases of Grapes

This lesson summarizes major grape diseases with a focus on symptom recognition, pathogen characteristics, epidemiology, and management strategies.

Downy mildew: Plasmopara viticola

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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.

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Pathogen

Mycelium is intercellular with spherical haustoria, coenocytic, thin walled and hyaline.

Sporangiophores arise from hyphae in the sub stomatal spaces. It branched at right angle to the

main axis and at regular intervals. Secondary branches arise from lower branches.The sporangia

are thin walled, oval or lemon shaped. The Zoospores are pear shaped, biflagellate and 7 – 9

micron meter. The oospores are thick walled.

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Mode of Spread and Survival

Through sporangia by wind, rain etc. 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.

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Disease Cycle

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Management

Spray Bordeaux mixture 1 % or Metalaxyl + Mancozeb 0.4 %.

Powdery mildew : Uncinula necator

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Symptoms

leaves.Malformation and discolouration of affected

leaves. Discolouration of stem to dark brown. Floral

Early berry infection results in shedding of affected

skin of the berries.

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Pathogen

White growth consists of mycelium, conidiophores and conidia. Mycelium is external,

septate and hyaline. Conidiophores are short and arise from external mycelium. Conidia are

produced in chain. They are single celled, hyaline and barrel shaped. The fungus is oidium type.

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Mode of Spread and Survival

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.

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Disease Cycle

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Management

Spray Inorganic sulphur 0.25 % or Chinomethionate 0.1 % or Dinocap 0.05 %.

Bird’s Eye Spot/Anthracnose: Gloeosporium ampelophagum ( Elsinoe amphelina)

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Symptoms

and in late stages these spots are surrounded by a dark

margin which gives it the “bird’s-eye rot”

appearance. The spots vary in size from 1/4 inch in

diameter to about half the fruit. The fungus also attacks shoots, tendrils, petioles, leaf veins, and

fruit stems. Numerous spots sometimes occur on the young shoots. These spots may unite and

girdle the stem, causing death of the tips. Spots on petioles and leaves cause them to curl or

become distorted.

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Pathogen

Mycelium is septate and dark colored. Conidia single celled oval and hyaline.

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Mode of Spread and Survival

Seed-borne-infected vine, cuttings and air-borne conidia. As dormant mycelium in the

infected stem-cankers. Warm wet weather. Low lying and badly drained soils.

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Disease Cycle

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Management

Removal of infected twigs.Copper oxychloride 0.2% or Mancozeb 0.25%

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Summary Cheat Sheet

Focus Area	Key Takeaway
Major diseases	Revise causal organisms, hallmark symptoms, and crop stage of attack.
Spread and survival	Link each disease with inoculum source, vector, and favorable conditions.
Management	Prioritize integrated management: sanitation, resistant varieties, and timely sprays.

References

1 source • [1]

[1]

Class notes and standard plant pathology references