Damage and nuisance

• Leaves

Known for more than two centuries, the symptoms caused by Colomerus vitis appear in the spring by the formation of galls on the leaves (Figures 1 and 2). Thus, small blisters of varying size are visible on the upper surface of the limbus, causing the latter to deform (figures 3 and 4). On the underside, there is a proliferation of hypertrophied whitish hairs, subsequently reddening (Figures 5 to 7).

• Petioles, tendrils, flower buds

Petioles, tendrils or flower buds (Figures 8 and 9) can also reveal the overgrowth of enlarged hairs. The rather dense down formed is initially white, then takes on a more or less pronounced pinkish hue depending on the grape variety, or even brown to red over time. These piliferous zones are due to the development of the cells of the epidermis following the nutritional bites of the Phytoptes which protect themselves inside these networks of hypertrophied hairs. In severe attacks, entire leaves may be blistered and covered with a whitish down on the underside. 

The galls formed on inflorescences cause sagging affected flowers but this is quite rare. Attacks on twigs can give young vines a bushy appearance, with stunted shoots reminiscent of the short-knot symptoms; the branches formed subsequently cannot be used for the training pruning. On older vines, the attacks are less damaging. We sometimes observe a fall of severely attacked leaves.

Note that the link between the severity of leaf damage and the qualitative or quantitative losses observed at harvest is controversial.