A Cover Crop System for Vineyard Pest, Weed and Nutrition Management
Large scale replicated trials were initiated in the fall of 1991 on three farms in the San Joaquin Valley. The first year’s data was collected during the 1992 season. In general, we observed an increase in the activity of natural enemies, especially spiders which resulted in a suppression of leafhopper numbers in some vineyards. The numbers of leafhoppers during the 1992 season were too low to observe a strong effect of cover crops on their numbers. Whole-vine spider exclusion and spider caging with leafhoppers indicated that the most common spiders in vineyards are important predators of leafhoppers. Continued monitoring of our vineyards is necessary to determine the long term effect of cover crops on the numbers of pests and their biological control agents. Our results on weed suppression with dry mulch is variable. However, our studies and those conducted by C. Elmore in north coast vineyards indicate that yearly accumulation of biomass in vine rows should provide sufficient weed suppression to minimize the use of herbicides. In table and wine grape vineyards, cover crops left to dry in row middles can suppress weeds, conserve soil moisture, decrease mowing costs, and reduce dust problems. The data on the nutritional status of vines did not show any treatment differences. This is not surprising, however, since the effect of cover crops on mineral nutrition of vines is a delayed effect, often not detectable until the following year. Our initial budget for alternative floor management systems indicates that the use of cover crops for weed management may increase the cost of grape production, primarily due to the added cost of cover crop seeds. This increased cost, however, should turn into savings when insecticide and fertilizer costs are included in the enterprise budget. It is anticipated that our cover crop system will reduce insecticide, herbicide, and fertilizer inputs. In the long term, seed costs should also be reduced, since the cover crops used in our studies are self-seeding.