Main symptoms

The short knot is responsible for the progressive dieback of the vines, its symptoms appear at random in the plots and subsequently develop in more or less large foci.

The leaves growing on diseased vines show various abnormalities in color and shape. We can therefore observe variegations or mosaics of golden yellow color located initially along the veins and then generalizing to all or part of the leaf blade. Sometimes rings or lines are visible by transparency on the young leaves. Anomalies in the morphology of the limbus are also observed: aberrant venation with asymmetries, double or irregularly cut leaves or with a more marked indentation.

Note that in the literature we sometimes speak of "reticulated variegation" to characterize the symptoms of short knotted associated with a strain of GFLV VB (for vein banding). It is characterized by the presence of more or less chlorotic bands along the veins, amplifying as the grapes approach maturity. “Enation disease” is also reported, linked to the GFLV EN strain (for grapevine enation). It is characterized by the formation of ridge-shaped growths on the underside of the leaves. These growths, also called enations, measure 2 to 3 mm in height and 3 to 5 mm in width and are more or less parallel to the main veins. Affected leaves are deformed and take on the appearance of a fan. Those most affected can fall prematurely.

The twigs are sometimes flattened, and above all reveal shorter internodes, sometimes double knots. They also show zig-zag growth, fasciations and bifurcations. The proliferation of short branches gives the vine a bushy shape.

Discolorations may appear on tendrils and clusters. The fertility of the latter is disturbed, coulure (fall of flowers or young fruits) and millerandage (lack of ripening of the vine leading to a partial abortion of the grape) can occur. In addition, the berries may later ripen irregularly, their quality deteriorated, and yields reduced.

Let us add that the formerly affected vines have a more limited root system, and that they very often end up dying.

• Damage

The court tied has repercussions both on the quantity of grapes produced, but also on their quality. Indeed, by weakening the vines, they become less productive. For example, moderately short tied vines have a yield reduced by 20 to 30%. In extreme cases, yield reductions can approach 80%. This situation is partly explained by the phenomena of coulure and millerandage which accompany this viral disease. The influence of the tied court on the quality of the harvested grapes varies according to the authors: without effect for some, obtaining grapes more concentrated in sugars and less loaded in organic acids for others. In the latter case, we could speak of the beneficial influence of the short knot if this was not done to the detriment of the productivity of the vineyard.

Finally, it should be noted that an affected plantation will remain so irreparably, and that, in extreme cases, premature uprooting of the vines should be considered.