The effects of feeding damage by the European red mite, Panonychus ulmi on the gas exchange of grapevine leaves (Vitis vinifera L.) were investigated. At mite infestation levels up to 3500 mite‐days per leaf (corresponding to a peak density of 60 mites/leaf), plants infested with P. ulmi showed no decrease in the photosynthetic rate. The same infestation level reduced transpiration only by 8.7%. Stomatal and mesophyll conductance were not affected by P. ulmi feeding. The results obtained in this investigation lead to the conclusion that the empirically defined economic injury level for P. ulmi of 2–5 mites per leaf, actually used by the viticulturists in Central Europe, is far too low.