Native grass ground covers in California vineyards provide multiple ecosystem services

Authors: DAANE, KENT - University Of California; Hogg, Brian; WILSON, HOUSTON - University Of California; YOKOTA, GLENN - University Of California

Submitted to: Journal of Applied Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/1/2018
Publication Date: 8/13/2018
Citation: Daane, K.M., Hogg, B.N., Wilson, H., Yokota, G.Y. 2018. Native grass ground covers in California vineyards provide multiple ecosystem services. Journal of Applied Ecology. 55:2473-2483.

Interpretive Summary: Crop fields are often inhospitable places for natural enemies of insect pests, and adding native plants to crop fields can provide food and habitat that natural enemies need to survive. Plants that are native to the area are more likely to benefit natural enemies than exotic plants. Native plants can be added to crop fields as ground covers, which are usually planted between the crop rows. Pest numbers typically decrease when ground covers are present, but the reasons for this reduction are often unclear. Natural enemies could be moving out of the ground cover onto the crop plants, or the ground cover plants could be directly benefiting the crop by improving the soil. We studied whether ground covers consisting of native perennial grasses affected pests, natural enemies, and soil and crop plant condition in a California vineyard. Vineyards either had bare soil, native grasses that were not irrigated, or native grasses that were irrigated during the summer. When native grasses were added to vineyards, numbers of leafhopper pests were lower, and spider numbers and parasitism levels on leafhoppers were higher. However, soil moisture was higher and plant stress was lower in vineyards with the native grasses. Reduced plant stress in vineyards with native grasses probably made plants less suitable for leafhoppers, which often prefer stressed plants. We conclude that beneficial effects of the native grasses on plant stress ultimately reduced numbers of leafhoppers, although it is possible that increases in spider numbers and parasitism levels also played a role.

Technical Abstract: The mechanisms responsible for the success or failure of agricultural diversification are often unknown. Most studies in this area have focused on enhancing the effectiveness of natural enemies, but non-crop plants can also improve pest suppression by changing the host quality of crop plants through competition for nutrients or water. Perennial plants that are native to the area are more likely to provide resources and long-term habitat to resident natural enemies than exotic annuals, and may require less maintenance. We conducted a three-year study in a California vineyard to examine the effects of ground cover consisting of native perennial grasses on pests, natural enemies, crop plant condition and soil properties. Three ground cover treatments were included: bare soil, non-irrigated native grasses, or native grasses that were irrigated during the summer. Numbers of leafhopper pests (Erythroneura spp.) decreased in both native grass treatments, where parasitism rates and spider densities were higher. Leaf water stress and available soil moisture were also significantly higher in the irrigated native grass treatment and, at times, in the non-irrigated native grass treatment, than in the no ground cover treatment. Berry weight was significantly higher in the irrigated treatment, but did not differ between the no ground cover and non-irrigated native grass treatments. Grape quality (brix) was not reduced in the native grass treatments compared to the no cover treatment, suggesting that increased soil moisture in the presence of native grasses did not compromise grape quality. We conclude that native grasses reduced host quality of grape vines for leafhoppers by moderating plant water stress through improvements in water infiltration in the soil, and possibly by providing food resources and/or habitat for natural enemies.