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Code: OIV 455

Name: Leaf: degree of resistance to powdery mildew

Category: , GROUP OF CHARACTERISTICS, ORGAN

Subcategory: POWDERY MILDEW, BIOTIC RESISTANCE - FUNGUS, LEAF - MATURE, LEAF - YOUNG

Description

The resistance of grapevine varieties to powdery mildew (Erysiphe necator) is to be observed under field trials over several years without the use of chemical plant protection and/or resistance inductors. Evaluation of the attacked patches of all the leaves from 4 - 6 vines at two periods, if possible: about 3 weeks after onset of flowering (growing leaves) and after vintage or before frost (mature leaves). 1 = Unlimited infection; complete or nearly complete attack of the leaves - ample mycelium and fungus fructifications. 3 = Vast attacked patches, some of them limited - leaf blade, partly attacked – obvious mycelial growth and fungus fructification. 5 = Attacked patches usually limited with a diameter of 2-5 cm. 7 = Limited attacked patches with a diameter of less than 2 cm - little mycelium and limited fungus fructification (the presence of Oidium is only indicated by a slight curling of leaf blade). 9 = Greatly suppressed symptoms or none at all – no mycelium or visible fructification (merely a slight curling of leaf blade). The symptoms should be evaluated considering the climatic conditions, that could influence the evolution of the disease, and, possibly, on plants without any biotic or abiotic stresses.

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