Innovative Under Trellis Management in Wine Grapes

2012 Summary by Alice Wise

In the spring of 2012 the CCE-SC grape research program received a multi-year grant from the Northeastern Sustainable Agriculture Research and Education program (SARE). This project is designed to explore the use of cover crops or mowing for management of the area under grapevines. The majority of eastern winegrape growers maintain this area with herbicides, considered to be the easiest and most cost effective strategy. Green growth under vines is often viewed as detrimental, competing with vines for water and nutrients. However, many growers endeavor to reduce pesticide use and are therefore seeking viable alternatives. Forty-six growers in eight states responded to a survey conducted last spring to document current practices and gauge interest. A webcast broadcast to fifty participants highlighted related work of two researchers and reiterated the benefits of cover crop strategies.

The first objective of the project is to document that more growers are adopting mowing and/or green covers under the trellis. This is an effort to reduce leachable nitrates, reduce or eliminate herbicides, and reduce canopy management inputs, saving vineyards money while maintaining or improving yield and quality. In 2012, five growers agreed to seed cover crops in their vineyards seeding a total of 17.25 acres. These plots included several types of clover and no mow fescue mix. In several cases, the expense of seed dictated the choice of cover. In one vineyard, clover plots did not germinate. Some growers were unwilling to host herbicide plots for comparison, understandable for those with a goal of avoiding herbicide use.

In three of four vineyards, there were visual differences in vine size and leaf color between groundcover treatments. In one vineyard, vines were noticeably larger in clover plots. In a second vineyard, vines with clover seeded in 2011 were much larger than vines with clover seeded in 2012. Fruit in these clover plots had lower sugar and higher acids at harvest, suggesting a delay in ripening. We have not yet taken pruning weights in the third vineyard. While the vine size difference was not surprising, we did not see this same result in our cover crop research study. Similarly, we have not found any differences in fruit ripening among treatments in our replicated cover crop study.

The second objective is to determine the impact of undervine mowing on vines. This trial involves four treatments: T.1 - season long mowing (5 times); T.2 - glyphosate only (3x); T.3- mowing (3x plus glyphosate early July); and T.4 - mowing (4x) plus glyphosate early August. It is located in a Merlot block at the LIHREC research vineyard in Riverhead, NY. There were no significant differences in shoot length (measured three times) or shoot diameter. Vine pruning weights have yet to be analyzed. Vine nutrition, as determined through the analysis of leaf petioles, was similar for all treatments with the exception of phosphorus, which was lower in the glyphosate only plots. There were no differences in yield or fruit ripeness at harvest. We were hoping that the use of green cover (potential competition for water and nutrients) would reduce berry size (higher skin:flesh is desirable in reds for color and flavor compounds) but we have not been able to document this effect. Lysimeters to gauge nitrate leaching will be installed in the spring of 2013.

The third and final objective of this project is to evaluate the impact of seeded under vine cover crops. This trial involves four treatments: glyphosate only (2x); Dutch white clover; no mow fescue mix; and a combination of clover and no mow. This trial is located in a Syrah block in a commercial vineyard on Long Island. There were no significant differences in shoot length or in shoot diameter. The six central vines in each plot were pruned on December 6. Vines in no mow plots were visually smaller though not statistically significant (p=0.0522). There may be differences next season if this trend continues. Pruning weights in the clover and herbicide plots were similar, unlike what was noted in several grower vineyards. In petiole analysis, though not statistically significant, there was a trend for lower petiole nitrogen in no mow plots. The two treatments with clover had significantly lower phosphorous levels. Phosphorous fertilization is often recommended when establishing clover for forage. Long Island soils however tend to be high in phosphorous due to a history of row crop vegetables prior to vineyard establishment. Lysimeters to gauge nitrate leaching will also be installed in this experiment in spring 2013.