Relative Infestation Level and Sensitivity of Grapevine Cultivars to the Leafhopper Empoasca vitis (Hemiptera: Cicadellidae).

The leafhopper Empoasca vitis (Göthe) (Hemiptera: Cicadellidae) feeds on veins of grapevine leaves, mainly on the phloem, causing physiological injury, color change and drying of leaf margins, yield and sugar content reduction. The relative infestation level (i.e., the probability that a plant is attacked by herbivores) of E. vitis on different grapevine cultivars and their sensitivity (i.e., the incidence of symptoms expression in response to herbivore feeding or other stimuli) to this pest were studied over four years in two vineyards located in northeastern Italy. Some cultivars (e.g., Carménère and Sauvignon Blanc) were usually more infested than others (e.g., Cabernet Sauvignon and Pinot Gris), although some differences were observed among years and sites. The sensitivity varied among cultivars, i.e., some of them showed more symptoms than expected on the basis of infestation levels (e.g., Carménère and Merlot), in contrast with others (e.g., Rhine Riesling and Chardonnay). Information obtained can be used within the framework of integrated pest management in vineyards. Action thresholds should differ on the basis of sensitivity. Sampling must first be carried out on the most susceptible cultivar and, if the action threshold is exceeded, it should be extended to the remaining cultivars based on their decreasing relative infestation level.