Damage and nuisance

• Leaves

Commonly called the "red spider", Panonychus ulmi is at the origin of the "leaden" appearance of part of the foliage during the summer. This symptom is caused by the numerous nutritional punctures of the mobile forms of this mite, which empty the cellular contents of the palisade parenchyma of the leaves. Thus, the blade of old leaves takes on a greenish-brown tint.

The upper part of the twigs is not immediately affected and the young leaves often retain their light green appearance which contrasts with that of the lower leaves. Note that unlike other species of mites, no web is observed.

This acariosis ultimately leads to a significant decrease in leaf photosynthesis, water loss, and premature leaf drop, which has the effect of altering the harvest quantitatively and qualitatively (the alcoholic strength in particular).