Mark Krasnow,* Tingting Zhang, and Allison Haywood
*Thoughtful Viticulture, PO Box 312, Blenheim, 7240, New Zealand (mkrasnow@gmail.com)

Due to increasing market pressure, and because of the development of herbicide resistance in weed species, it is important for the industry to reduce, and eventually eliminate, herbicide use in vineyards. This trial was set up to assess the effects on vine growth, yield, and fruit composition of multiple herbicide sprays (the industry standard) versus a mixed management strategy of single herbicide spray before budburst, with any additional weed-control passes being nonchemical (undervine mowing or cultivation). The vineyards were set up as split plot designs with five sampling loci in each plot. The trial was conducted in three Merlot vineyards in Hawke’s Bay and three Sauvignon blanc vineyards in Marlborough, New Zealand. Undervine vegetation was significantly different among treatments in all vineyards from flowering onward, with mixed management having more grass and clover undervine, and multiple herbicide having more bare area. There were rarely significant differences in stem water potential throughout the season and in canopy gap percentage at flowering, veraison, or harvest, suggesting that the vegetation that grew after the first herbicide spray in the mixed treatment did not compete with the vines to such an extent that their growth was greatly limited. The reduced herbicide use did not greatly affect yield or fruit composition, demonstrating that mixing in nonchemical weed control methods is a viable option in vineyards, and one that will not engender resistance in weed species. It is hoped that the findings of this study will embolden more growers to reduce their reliance on chemical methods for weed control in vineyards and to begin to employ more nonchemical means moving forward.

Funding Support: New Zealand Winegrowers and New Zealand Ministry of Business, Innovation, and Employment