Leafhoppers (Homoptera: Cicadellidae) were surveyed in Western Oregon vineyards in 1999. Four sites were sampled for leafhoppers using a sticky trap method, and 29 vineyards were sampled for leafhoppers using a sweep net method in the summer of 1999. The sticky trap and sweep net methods were chosen based on cost, ease of use, and the fact that they are commonly used tools available for growers and IPM programs. Populations varied according to sample method, date, location, height, agricultural practices, and growing region. Each method resulted in the capture of different leafhopper species. Sticky traps attracted, and caught mobile insects such as the winged adults. The sweep net captured leafhoppers of all stadia from the vegetation. There was seasonal variation seen for each leafhopper group. Greatest numbers of leafhoppers were caught on the border and edges of the vineyard, presumably because of the surrounding vegetation providing refuge and food. The height of catch was dependent upon the preferred host plant of the leafhopper. Species that feed on the grapevine were generally found in the canopy from 90 to 150 cm above the soil surface. Vineyard management influenced abundance and diversity within the sites. Those vineyards using the least input had the highest diversity and lowest overall abundance of leafhoppers. Chemical use, irrigation, and cover crop choice influenced the species composition of the vineyard. The sites to the south of the Willamette Valley had a higher abundance of the species Psamotettix sp. The community structure of leafhoppers appeared to be more similar in the southern sites to California. The vineyards that had a diverse mix of plants in the cover crop had a more diverse population of leafhoppers. Most species found in this study feed on herbaceous plants that are common as vineyard ground cover. The cover crop that most low input management sites use may increase the number of leafhoppers that feed on the vine, but the presence of a cover crop has many advantages in the vineyard system. / Graduation date: 2001