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Uncinula necator (Schw.) Burr.

Mycologia, ASCOMYCOTINA, ERYSIPHALES, ERYSIPHACEAE .

Crops attacked: grapevine .


[R]Common Names :

Powdery mildew,

Always present with high temperatures (25-28 C.), without rain. It exists in Europe since 1845 and in Portugal since 1847.

Identification, Description, Biology, Epidemiology, Treatement, Possible misleading, Images


[R]Identification
The powdery mildew is visible under naked eye as a white-greyish downy grouth that may cover the leaves, young shoots and bunches. The fungus cannot be grown in artificial media (obligate parasite).

[R]Description
In the shoots, brown spots with a white-greyish powder originating deformations in the younger ones, and yellow brownish spots with fibrous-looking edges in the mature ones. In the leaves, light brown spots in the veins of the leaf (lower surface) originating deformations with wavy and crinkly aspect; greyish-white dusty outer covering, on the leaf surfaces.
In the clusters, death and fall of flowers and young berries and splitting of the developing ones (the susceptibility ceases when the sugar contents reaches 12-15%); powdery appearance similar to the leaves.

[R]Biology
The fungus overwinters, resisting to the adverse conditions as sexual fructifications (cleistothecia) and also as dormant mycelia, protected by the bud scales (main form of maintenance). The infections take place from this mycelium and also from the sexual spores; (ascospores).
The superficial mycelia that forms, penetrates in the host epidermal cells through haustoria; externally conidiophores are formed which produce assexual spores (conidia) in chains, originating the secondary infections; in autumn, cleistothecia are formed from the subtle mycelia that covers the leaves and the immature tips of the shoots.

[R]Epidemiology
The conditions favourable to the attack of this parasite are: temperatures of 25-28 C.(optimal), after the bursting of the shoots, and absence of water; the attack starts from the dormant mycelia of the buds and from the ascospores (primary infections) or from conidia (secondary infections); the ascospores have a low range of dissemination (limited to places where the disease occurred in the previous year); the conidia are carried out by the wind and, both germinate on the green surfaces in the absence of water (rain or condensation).

[R]Treatement
Chemical curative and preventive control, the last one taking into account the critical periods and forecasting warnings.

[R]Possible misleading
In the initial phase of the attack, at the primary symptoms, confusions with the characteristic oily spots due to downy mildew ( Plasmopara viticola ).

[R] Images

  1. Uncinula necator , Grapevine powdery mildew (THOMAZ I., MA)
    Grapevine powdery mildew Immature grapevine shoot showing powdery mildew mycelium and some cleistothecia (perithecia).
  2. Uncinula necator , Grapevine powdery mildew (THOMAZ I., MA)
    Grapevine powdery mildew Upper surface of grapevine leaves showing powdery mildew mycelium and cleistothecia (perithecia) resulting from a late infection.
  3. Uncinula necator , Grapevine powdery mildew (THOMAZ I., MA)
    Grapevine powdery mildew Downy cover of powdery mildew on maturing grapes and rachis.
  4. Uncinula necator , Grapevine powdery mildew (BASF)
    Grapevine powdery mildew Downiness due to powdery mildew on bunches of grapes.
  5. Uncinula necator , Grapevine powdery mildew (CARTOLARO P., INRA)
    Grapevine powdery mildew Cleistothecia (= perithecia) of powdery mildew on a grapevine leaf.
  6. Uncinula necator , Grapevine powdery mildew (CARTOLARO P., INRA)
    Grapevine powdery mildew Cleistothecia (= perithecia) of powdery mildew on a grapevine leaf shown in more detail.
  7. Uncinula necator , Grapevine powdery mildew (BASF)
    Grapevine powdery mildew Grapes bursting because of powdery mildew.
  8. Uncinula necator , Grapevine powdery mildew (BASF)
    Grapevine powdery mildew Grape bursting because of powdery mildew, shown in detail.
  9. Uncinula necator , Grapevine powdery mildew (CARTOLARO P., INRA)
    Grapevine powdery mildew Chains of powdery mildew conidia on the surface of a grape leaf (dissecting microscope).

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