Evaluation of Potential Cover Crops for Inland Pacific Northwest Vineyards

¹ Department of Horticulture and Landscape Architecture, Washington State University, Prosser, WA 99350 [present address: Department of Horticulture, Michigan State University, East Lansing, MI 48824-1325]
² Viticulture and Enology Research Center, California State University-Fresno, 2360 East Barstow Ave M/S VR 98, Fresno, CA 93740-8003
³ USDA, ARS National Temperate Forage Legume Germplasm Resources Unit
⁴ USDA, ARS Horticultural Crops Research Unit, 24106 N. Bunn Rd., Prosser, WA 99350

email: neumann6{at}msu.edu

Numerous cover crops for orchards and vineyards have been evaluated, but many selections do not necessarily perform well in the cold, arid environment of the inland Northwest. A cover crop between vine rows can mitigate wind erosion and subsequent damage to young vines. However, low rainfall, gusty winds, and sandy soils that cause significant wind erosion problems can exacerbate cover crop establishment, and cold winters can limit cover crop survival. During 1998, 175 plant accessions were screened for performance as vineyard cover crops at Prosser, Washington. Assessed attributes included percent emergence, percent vegetative cover, stand duration, and plant height. Based on that assessment, seven domestic selections and four foreign Medicago species (medics) were identified for additional evaluation in a research trial in 1999. Additionally, seven accessions and two mixes of species that met the growth criteria and had commercial availability were evaluated in a commercial, drip-irrigated vineyard near Prosser in 1999. Vine water potential and soil moisture were determined in addition to the identical growth criteria from the 1998 study. Cover crop treatments did not lead to detectable water stress in the vines (midday y = -0.84 to -1.30 MPa). However, dry soil between vine rows due to precision drip irrigation inhibited germination and establishment of legumes; therefore, grasses had better emergence rates. Of the mixed species, a grass mix (Canada) composed of crested wheatgrass (Agropyron cristatum L.), pubescent wheatgrass (Elytrigia intermedia L.), and perennial rye (Lolium perenne L.; 40:40:20), depleted soil water the least and showed the least effect on vine water potential. Early season weeds were suppressed by most cover crop species; however, season-long suppression of weed growth was observed only for the Canada mix and crested wheatgrass cv. Fairway.

Note:
Acknowledgments: We would like to thank the Washington Wine Advisory Committee, Northwest Center for Small Fruits Research, Washington State Grape Society, and Washington Association of Winegrape Growers, for funding and scholarship money provided and Corus Brands for use of their vineyard. We are grateful for the technical support of Lynn Mills, Alan Kawakami, Sally Longoria, and Julie Schaneman. Research conducted at the Washington State University Irrigated Agriculture Research and Extension Center, 24106 N. Bunn Rd., Prosser, WA 99350.

Key words: Cover crops, Vitis vinifera L., evaluation techniques, vineyards

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