INVESTIGATING ANNUAL UNDER‐VINE COVER CROPS AS AN ENVIROMENTALLY SUSTAINABLE ALTERNATIVE TO HERBICIDES IN NORTHEASTERN VINEYARDS
SARE 2013 GRADUATE STUDENT GRANT IN SUSTAINABLE AGRICULTURE AWARDED TO
M.S. Student at Cornell University
SECOND YEAR OF STUDY COMPLETED BY ADAM KARL
M.S. Student at Cornell University email@example.com
Considerable assistance provided by TAYLOR MATTUS
M.P.S. Student at Cornell University
The rising concerns of herbicide resistance, runoff, and environmental contamination—coupled with increased consumer desire for sustainably produced wine—warrant investigating alternatives to herbicide use in vineyards.In the Northeastern U.S. cover crops are generally only grown between rows, while an herbicide strip is maintained under the grapevines. Previous work in warmer, humid climates has shown that perennial cover crops planted directly beneath vines induce competition that can improve canopy structure and reduce undesirable excessive vigor. Yet in colder regions like the Northeast, growers must mound soil over the graft unions of Vitis vinifera vines, like the economically important variety of Riesling, and therefore an established perennial under‐vine cover crop is not an option. This proposal was to fund continued research that compares two annual species of cover crops, chicory and buckwheat, planted directly underneath Riesling grapevines, to the conventionally bare soil maintained with glyphosate. How under‐vine cover crops affected vine vegetative growth, harvest yields, fruit and juice characteristics were examined for the third and fourth years of under‐vine cover crop establishment. A split‐plot irrigation design that enabled half of the treatment vines to be watered throughout the season went unused through the study, as the climatic conditions for 2014 and 2015 did not require vineyard irrigation. The study revealed that chicory used as an under‐vine crop eliminated the need for herbicide use, but resulted in considerably diminished vine size and, in 2015, diminished yield. Shoot growth was reduced, a positive attribute in the vigorous vineyard. Titratable acidity of the fruit in the chicory treatment was decreased, likely due to increased cluster light interception. When used as an under‐vine cover crop, buckwheat generally had little impact on yield, vine size, petiole nutrients, and fruit composition, suggesting it could easily be used as a replacement for herbicide use in vigorous vineyard. Chicory reduced vine size and, when used with caution, may be a useful tool for de‐ vigorating large vines.
Statement of the problem, rationale, and justification
The purpose of this project was to investigate the continuing effects of using annual cover crops as a sustainable alternative to herbicide in under‐vine rows, in a Riesling vineyard located in the Finger Lakes wine region of New York State. Currently, most Northeastern wine grape vineyards eliminate potential competition for water and nutrients by maintaining a weed‐free zone under the trellis using herbicide. However, in the Northeast where there is frequent rainfall throughout the growing season and deep, nutrient rich soils, grape growers struggle with excessive growth in vineyards. Vines that produce excessively large canopies create shading and conditions for disease, which are known to inhibit the development of high quality fruit. Growers must then resort to costly canopy management practices including leaf removal, hedging, and cluster thinning to mitigate the vigor. The use of any herbicide also poses risk of increased resistance in the weed community, leaching and runoff, and environmental contamination. Bare soil left exposed after herbicide use is also vulnerable to erosion, crusting, soil structure degradation, and rapid water runoff.
Planting annual groundcovers under the trellis may provide an innovative, easily implemented and cost‐effective method for reducing herbicide use, soil erosion, and the need for expensive canopy management practices while improving fruit and wine quality. Our recent work has demonstrated few detrimental impacts of annual cover crops that do not vigorously compete with vinifera vines, resulting in the ability to replace the herbicide strip with a cover crop. However, until this project, there was no long‐term data on the impact of vigorous cover crops like chicory on mature cool‐climate vineyards that require hilling of soil over the grant union.
The goal of this experiment was to test the hypothesis that annual cover‐crop species could be used to suppress vine vigor and improve fruit and wine quality.
The original study was planned for only the 2012 and 2013 growing seasons, which were only the first and second year of cover crop establishment at the experimental site. While few significant differences in vine growth were reported from the first growing season, fruit composition was improved by the presence of under‐vine cover crops, with lower reported acid levels. Previous research has shown that cover crops can induce the greatest effects after the third or fourth year of establishment. The SARE funding provided us with the ability to test these cover crops in their third and fourth years.
To determine if annual cover crop species planted in under‐vine rows reduce excessive vine vegetative growth and vigor and improve canopy architecture, resulting in improved fruit and wine quality.
Evaluate if under‐vine cover crops compete with grapevines to alter vine water and nutrient status.
Evaluate the long‐term effects of using annual under‐vine cover crops by continuing to test under‐vine cover crops as a sustainable alternative to herbicide on Riesling vines on the same site located in the cool and humid Northeast for the third and fourth years of data collection.
To promote sustainable vineyard floor management alternatives like under‐ vine cover crops in cool and humid climates to researchers and growers.
Materials and Methods
The project was in flux due to the grant awardee, Lindsay Jordan, returning to Cornell after the start of the 2014 growing season (June), and then departing from her graduate program in August of that year. Other program students and technical staff filled in for the remainder of the season. In 2015, graduate student Adam Karl took over the project, but then departed Cornell in August with the remainder of the project being completed primarily by another graduate student Taylor Mattus. Due to the lack of staff, the methods detailed in the proposal were modified.
Briefly, buckwheat (Fagopyrum escolentum) and chicory (Chicorium intybus) were established underneath mature Riesling (cl 110/9 on 3309C rootstock) grapevine canopies in late‐May of each year in the former herbicide strip (approximately 1 m wide strip beneath the canopy) (Figure 2). Planting rates were 350 lbs/acre and 5 lbs/acre, respectively. Cover crops were planted by hand, although due to our success with this and other under‐vine cover crop projects, as well as considerable interest from the industry, the Finger Lakes Grape Program staff are planning development of a mechanized method for seeding under the trellis.
The vineyard alleys (approximately 2 m between former herbicide strips) were maintained as resident vegetation, which was primarily fescue with a wide range of weed species depending on the time of the season and the year. The control plots were maintained with glyphosate sprayed at 64 oz/acre twice during each growing season.
Shoot growth rate was collected by determining the length of nine flagged shoots per experimental unit every week to ten days. Pruning weights from dormant canes from the previous season were taken in March of each year. Vines were dormant pruned to four, 10‐node canes with renewal spurs. Prunings were weighed on a per vine basis with a hanging scale accurate to 0.01 kg. From within each experimental unit, 50 petioles were cut from leaf blades and shoots at berry set and veraison. Samples were then gently washed in a mild soap solution, rinsed with deionized water, stored in paper bags, and dried at 90oC for one hour. Samples were then submitted to the Cornell Nutrient Analysis Laboratory for combustion analysis of C and N and dry ash extraction of Al, B, Ca, Cu, Fe, K, Mg, Mo, Mn, Na, P, and Zn.
At harvest, the grapes from each treatment replicate were hand cut and weighed with the hanging scale. A sample of 100 berries per treatment was weighed to determine average vine size.
Samples from harvest were frozen immediately at ‐20oC. The juice was thawed and warmed in a water bath at 60oC for 30 minutes and then allowed to equilibrate to room temperature before analysis of soluble solids, pH, and TA. TA was measured by titrating 10 mL of juice with 0.10 M NaOH to a pH of 8.2 using an automatic titrator.
The general methodology for the experiment is presented in Figure 3.
Data were analyzed as a split plot with irrigation as the main plot and cover crop as the sub‐plot (Figure 2) using SAS. Since irrigation was not run in the 2014 or 2015 seasons, the report focuses on main effects of cover crops.
The third and fourth years of the study provided very interesting data that can be used to inform decisions about under‐vine cover crops. This site provides our longest continuous use of chicory and buckwheat as under‐vine cover crops.
By the third and fourth year of the study, weed competition with under‐vine cover crops had been reduced to almost nothing. Both buckwheat and chicory competed extremely well with weed pressure underneath the grapevine canopy.
Vegetative growth of vines, as reflected by shoot length, was reduced by both buckwheat and chicory in 2014 (Figure 4), with differences being apparent to the visual eye (Figure 5). The pruning weight data for the same year backed up this observation, although the pruning weight of buckwheat was not as low as chicory despite the similar shoot lengths (Figure 6), suggesting that average shoot weight was greater in the buckwheat treatment than in the chicory (shoot number was adjusted early in the growing season). Shoot length was not collected in 2015, but pruning weights of vines in each treatment were similar to 2014 (Figure 6).
Yield per vine was impacted by treatments in 2015 only, with chicory vines producing lower yield than the buckwheat and control vines (Figure 6). Crop load (a ratio of reproductive to vegetative growth) was impacted in both 2014 and 2015, but results were inconsistent.
When combined with our two earlier seasons of data (2012 and 2013) we conclude that chicory devigorated the vine, resulting in a reduction in yield. Buckwheat tended to have little impact on vine size and yield, but may reduce average cane weight.
The impact of under‐vine cover crop on fruit maturity was inconsistent (Table 1), a similar result to our observations from the first two years of the study. There were considerable differences in titratable acidity (TA) in 2014, with differences of more than 1 g/L between the control and the chicory treatment. This difference can likely be attributed to the reduced vegetative growth in both under‐vine treatments, as cluster temperature was likely increased in the small vines, resulting in increased cluster temperature and increased acid degradation. Differences in soluble solids as reflected by brix are generally considered inconsequential as chaptalization of Riesling is a common practice in the region.
Despite four years of under‐vine cover, the petiole analysis at berry set for 2015 (Table2) demonstrated no differences among treatments, although molybdenum and phosphorous were both below recommended concentrations in all treatments. By veraison of the same year (Table 3), significant differences existed among treatments for both boron and phosphorous, although both nutrients were within recommended ranges. As the soil at the site is predominantly Hudson‐Cayuga silt loam with an organic matter of >3%, it is not surprising that nutritional differences are minimal.
As a result of this work, our research group has formulated recommendations for wine grape growers to experiment with the use of under‐vine cover crops in their vineyards. The recommendations are as follows:
1. To eliminate the need for herbicide strips in mature vineyards with little impact on vine size or fruit composition, buckwheat can be planted in late‐ May in upstate NY at a rate of approximately 350 lbs/acre.
2. To eliminate the need for herbicide strips in mature, vigorous vineyards, dwarf chicory can be planted in mid‐ to late‐May at a rate of approximately 5 lbs/acre. Pruning weight and Ravaz index should be monitored on sentinel vines each season to ensure the vines are not overly devigorated.
Education & Outreach Activities and Participation Summary
This project, in addition to our lab’s other under‐vine studies, have been garnering considerable interest from members of the wine and grape industry. The following presentations/discussions included data from the SARE‐funded portion of this study:
Chou, M.Y., A.D. Karl, L.M. Jordan, and J.E. Vanden Heuvel. 2016. Ground cover management for cold climate grapes. Northeastern New York and Vermont Winter Grape School, March 17, 30 participants, contact hours = 15.
Vanden Heuvel, J.E. 2015. Under‐vine cover crops for vinifera vineyards. BEV NY, Feb 28, 200 participants, contact hours = 100. BEVNY2015-2
Karl, A., Vanden Heuvel, J.E., S. Lerch, R. Sirianni, M. Brown, and I. Merwin. 2015. Under‐trellis cover crops as alternatives to herbicides. NY Fruit and Vegetable Expo, January 21, 100 participants, contact hours = 50. NYFruitVegExpo2015
Vanden Heuvel, J.E. 2015. Under‐vine cover crops to reduce vine vigor in vineyards. Finger Lakes Grape Growers Twilight Meeting, August 25, 30 participants, contact hours = 15. FLGG Twilight Meeting 2015