Vineyard weed communities were examined under four dormant-season cover-crop systems representative of those used in the north-coastal grape-growing region of California: no-till annuals (ANoT) (rose clover, soft brome, zorro fescue), no-till perennials (PNoT) (blue wildrye, California brome, meadow barley, red fescue, yarrow), tilled annual (AT) (triticale), and a no-cover-crop tilled control (NoCT). Treatments were carried out for 3 yr in the interrows of a wine grape vineyard. Glyphosate was used to control weeds directly beneath the vines, in the intrarows. Treatments significantly impacted weed biomass, community structure, and species diversity in the interrows. Orthogonal contrasts showed that tillage, and not the presence of a cover crop, impacted interrow weed biomass. Distance-based redundancy analyses (db-RDA) revealed significant effects of the cover-crop systems and of tillage on weed community structure in the interrows. For scarlet pimpernel and spiny sowthistle, the combination of ANOVA and orthogonal contrasts confirmed their association with the tilled treatments, as revealed by db-RDA. This same approach identified the association between California burclover and the no-till treatments. Our findings of no significant effects of the cover-crop systems on weed biomass, community structure, or diversity in the intrarows demonstrate that the impacts the cover-crop management systems had on the interrows did not carry over to adjacent intrarows. In addition, the fact that the cover crops did not affect vine yield, growth, or nutrition relative to the no-cover-crop control suggests that cover crops are likely to minimize soil erosion from winter rains, which is the primary purpose of vineyard cover cropping in northern California, without adversely affecting vine health or weed control.

Nomenclature: Glyphosate; blue wildrye, Elymus glaucus Buckley ELYGL; California brome, Bromus carinatus Hook. & Arn. BROCN; California burclover, Medicago polymorpha L. MEDPO; meadow barley, Hordeum brachyantherum Nevski HORBR; red fescue, Festuca rubra L. FESRU; rose clover, Trifolium hirtum All. TRH14; scarlet pimpernel, Anagallis arvensis L. ANGAR; soft brome, Bromus hordeaceus L. BROMO; spiny sowthistle, Sonchus asper (L.) Hill SONAS; triticale, X Triticosecale rimpaui Wittm. TRITI; yarrow, Achillea millefolium L. AMARE; zorro fescue, Vulpia myuros (L.) K. C. Gmel. VLPMY; wine grape, Vitis vinifera L. ‘Merlot’.