Monday, 18 June 2018

A pest on grapes

Uncinula necator or powdery mildew, a basidiomycete, is a pest on grapes. Its septate hyphae forms a mycelium on the surface of the leaves similar to a spider web. Special hyphal branches, the haustoria, penetrate the host cells to absorb food substances, thereby weakening the grape and reducing the harvest.

This fungus is recognizable by the appearance of pale yellow spots on the leaf, where after on the leaf and on the berries white powdery fungus spots are formed. At first, the growth points and the young leaf are affected, later the mature leaves and the grapes.

The fungus overwinters in the buds or on the old wood, where small yellow or black spots are visible. In spring as the buds will open, the fungus becomes active and touches the growth points. In spring, especially in fairly humid and warm weather and at an average day temperature of 8 °C, an extensive contamination can be expected.

Keeping the plant open ensures that it dries quickly, avoiding the mildew to expand significantly. The newer grape varieties are better resistant to fungi. In case of attack chemical treatment is possible by spraying with an extract of horsetail (Equisetum arvense) or with a sulfur solution.

Prepared slide by Lieder

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