Enhancing plant diversity for improved insect pest management in northern California organic vineyards
We present the results of studies in organic vineyards in Mendocino and Sonoma counties, California, in an effort to systematize the emerging lessons from our experience on vineyard biodiversity enhancement for ecologically-based pest management. In the Mendocino study, a vegetational corridor connected to a riparian forest channeled insect biodiversity from surrounding habitats into the vineyard, thus overcoming the restricted spatial limits to which the positive influence of adjacent vegetation on vineyard pest dynamics is usually confined. In addition, summer cover crops substantially enhanced biological control of leafhoppers and thrips, by breaking the virtual monoculture that vineyards become in the summer after winter cover crops dry out or are plowed under. In the Sonoma vineyard, an island of flowering shrubs and herbs provided season-long flower resources and alternate preys/hosts for natural enemies, which slowly built up in the adjacent vineyard. The island acted as a push-pull system for natural enemies, enhancing their activity but confining them mostly to the adjacent vine rows. Planting strips of summer cover crops could be a strategy to overcome the push effect of the island.