The effects of reducing herbicides in New Zealand vineyards

Abstract

Context and purpose of the study – Herbicides are commonly sprayed in the vine row to prevent competition with vines for water and minerals and to keep weeds from growing into the bunch zone. Sprays are applied before budbreak and reapplied multiple times during the season to keep the undervine bare. There is growing concern about the negative effects of herbicides on humans and the environment, and weeds in New Zealand have developed resistance to herbicides. Therefore, it is imperative that we reduce our reliance on herbicides in viticulture and incorporate methods that do not engender resistance.

Material and methods – This trial was conducted in the 2016-17, 2017-18 and 2018-19 seasons in three Merlot and three Sauvignon blanc vineyards in New Zealand. The trial was a split plot, with half the vineyard receiving multiple sprays (the industry standard). The other half received a single spray around budburst, and any subsequent undervine weeding was done using nonchemical methods (mowing or cultivation). In each vineyard half, five sampling locations were established for vine, fruit, and undervine measurements. Vines were assessed for canopy gaps by image analysis, yield, and rot severity. Fruit was sampled during ripening and at harvest to assess differences in chemical composition. The undervine area was surveyed at budburst, flowering, veraison, and harvest to assess differences in bare area and presence/abundance of various plant species.

Results – Reducing herbicide had a dramatic effect on the percent bare area under vines, as well as the species of undervine vegetation from flowering onwards. In most vineyards, canopy growth was similar for both the control (C) and reduced herbicide (RH) treatments, though a few differences were found, generally with the RH treatment having more gaps. A few differences were found in midday water potential, with the RH treatment generally having more negative SWP. Despite differences in canopy gaps and SWP, there were few effects on berry size or soluble solids. There were few other fruit compositional differences, though the RH fruit tended to have lower yeast assimilable nitrogen (YAN) than the C fruit. Yield was generally not affected by reducing herbicide, and rot severity tended to be similar between treatments, indicating no negative effects on fruit quantity or health from allowing more vegetation to become established under vines. These data show that herbicide use can be reduced by 50-75% with little negative effect on grapevines or their fruit. It is anticipated that adopting this technique will reduce herbicide residues in/on fruit and slow or stop the spread of herbicide resistant weeds.