Excessive weed growth in the area under the grapevine trellis can provide competition that is detrimental to yield and fruit quality. Typically, this strip is maintained through timely applications of herbicide. The goal of this project was to evaluate several alternatives to herbicides for use in vineyards. In 2006, we evaluated several species of native plants under the trellis with the goal of maintaining minimally competitive groundcover that would exclude other weed species. Poor seed germination occurred in both research vineyard and commercial vineyard plots. Re-establishment of these plots was not realized because sources of fresh seed were not available. An under trellis mowing study was conducted in a commercial vineyard during the 2005-6 seasons. Weed control with glyphosate was compared to mowing only. Generally, there was no significant difference between treatments. In spring 2008, a tractor-mounted under trellis mower was purchased through a Cornell University grant. Replicated plots were established at the Long Island Horticultural Research and Extension Center research vineyard. Preliminary data on the use of the unit and its impact on weed ecology were documented. Maintenance of these plots through future seasons will allow a rigorous evaluation of impacts on vine size, vine health and fruit quantity and quality.
The economy of eastern Long Island is closely linked to tourism and agriculture. As in many regions, these two industries have become inextricably linked through premium farmstands, agri-tourist activities such as hay rides and corn maizes, and through winery tasting rooms. The wine industry on Long Island is a vital part of agriculture, embodying the shift to high value commodities. It supports local and regional businesses and is a major employer. Many vineyards have committed land to preservation programs, helping to maintain precious open space in the face of encroaching development.
Control of vegetation in the strip under the trellis is a standard practice in the management of vineyards in the northeast. The goal is to minimize competition at key vine phenological stages, particularly between bloom and veraison. Excessive weed growth at these times can impair fruit quality and quantity. Typically, weed control is achieved through the use of herbicides. However, the infiltration of herbicides into groundwater has motivated growers to seek alternative methods. Cultivation is practiced by some vineyards with tractor mounted cutter blades, grape hoes, rotary hoes and tine weeders. While effective, cultivation is time-consuming, destroys vine roots and sometimes vine trunks, aggravates soil erosion and worsens compaction. This project addresses the feasibility of less common strategies, the maintenance of minimally competitive green cover and season-long mowing of weeds under the trellis.
1. Evaluate living mulch species under the grapevine trellis for percent groundcover, infiltration of other weed species and impacts on vine health and fruit quality.
2. Assess the impact of mowing under the trellis as a means of managing vegetation and gauge its impact on weed ecology, vine health and productivity.
1. Under trellis ground covers – Replicated plots in the LIHREC research vineyard and two commercial vineyards were seeded in fall 2006 with either red sandspurry (Spergularia rubra), knawel (Scleranthus annus) or Dutch white clover (Trifolium repens). All are low growing, the first two are native species, self-seeding once established. Plots were raked then seeded either on August 29 or September 5. In each of the seeding dates, rainfall occurred within 24 hours.
2.(a) Under trellis mowing – The cooperating grower purchased a custom unit with a mower head mounted on to a row middle deck mower. The mower head was mounted on a swing away arm to accommodate vine trunks. The goal of mowing under the trellis as well as in the row middle was to avoid herbicide use and save labor. The cooperator agreed to perform all mowing of plots as a part of the standard vineyard management regime. The timing and number of times that mowing took place was not recorded.
In 2005, we conducted this work on one site with very sandy soil. The warm, dry summer discouraged weed growth, thus limiting the relevance of the data. In 2006, we duplicated treatments on the sandy site and added a second site with slightly heavier soil to gauge treatment efficacy on different soil types.
In 2006, treatments included mowing only, glyphosate once in June and glyphosate twice in May and June. Credit 4WS with 1.5 lbs./a ai glyphosate (NuFarm Inc., Burr Ridge, IL) was applied May 4 and June 29. A RCBD design with four 3-panel plots per treatment was used. Treatments were applied as a directed spray with a CO2 pressurized backpack sprayer utilizing an 8003 LP flat fan nozzle, 25 psi, 30 gpa water.
As a means of gauging vine nutrient status, petioles were collected at bloom (late June) and postveraison (early September). Randomly collected petioles from all plots within a treatment were combined so that one sample was analyzed per treatment.
Percent cover and weed species were rated on following dates: April 28, May 31, July 26, August 30 and October 2, 2006. All weeds within a 15 sq.ft. area were evaluated.
Immediately prior to harvest, 200 berries per treatment were randomly sampled to gauge fruit ripeness and berry weight. Samples were taken Oct. 13 from site two and Oct. 23 from site one. Brix, titratable acidity and pH were done using standard protocol at LIHREC.
Harvest data was collected on October 13 from site two and on October 21 from site one. Clusters per panel (center panel only of the 3-panel plots, 4 plots per treatment) were counted and harvested into a lug (harvest tray). The lug was weighed so that an average cluster weight could be calculated.
2.(b) 2008 mowing trial at LIHREC
In spring 2008, an Edwards (Edwards Equipment Co., Yakima, WA) under trellis mower was purchased with a grant from the College of Ag and Life Sciences, Cornell University.
Replicated plots were established in a block of mature grapevines cv. Merlot located at the Long Island Horticultural Research and Extension Center, Riverhead. All treatments focused on management of weeds in the 2.5 ft. strip under the grapevine trellis. Treatments were as follows:
1. mowing only (May 29, June 17, July 14, Aug. 19).
2. glyphosate only (May 8, June 19, Aug. 13) – Credit (NuFarm Inc., Burr Ridge, IL) postemergence herbicide, 1 qt.acre equivalent plus 0.0025% NIS, 26 gpa water, 30 psi, 8003LP flat fan nozzle applied in directed sprays with a CO2 backpack sprayer.
3. mowing twice (May 29, June 17) then glyphosate July 11.
4. mowing three times (May 29, June 17, July 14) then glyphosate Aug 13.
Weeds were rated on May 19, June 11, July 7 and 28, Aug 10, Sept 11 and Oct. 10. Ratings were done by placing a 1 ft.9” x 3.5 ft. PVC frame in a randomly selected area of each plot. Percent weed cover was assessed within the frame, percentages were then categorized into winter annual grasses and broadleaves, perennial grasses and broadleaves, summer annual grasses and broadleaves.
As a means of gauging vine nutrient status, petioles were collected postveraison (late August). Randomly collected petioles from all plots within a treatment were combined so that one sample was analyzed per treatment.
Berry samples were collected on Oct. 14. From each of the four plots/treatment, 100 berries were randomly sampled. Berry weight was determined by weighing the 100-berry samples prior to crushing fruit for analysis. Samples were analyzed at LIHREC for Brix, titratable acidity and pH. Individual vines were harvested on Oct. 15. Crop weight and cluster number per vine were recorded. For each treatment, berries were counted on a random sample of 10 clusters.
Data was analyzed using JMP statistical program oneway anova with a Students t test for means separation. Data was log transformed prior to analysis.
1. Under trellis ground covers – In the two commercial vineyards and the LIHREC research vineyard seed germination was poor to non-existent. Rainfall was adequate after seeding. In past trials with these species, we have suspected that lingering levels of preemergence herbicides may have suppressed fall seeded covers. However, the research vineyard had not received preemergence materials of any type for seven years. We suspect seed quality was poor, though seed came from both local harvest and a commercial source. We intended to reseed plots in 2007 but were unable to locate seed sources for any of the species despite visiting several sites where these weeds had been seen growing in previous seasons. Because of insufficient amounts of fresh seed, this component of the project was abandoned.
2. Under trellis mowing – 2006
Full bloom petiole analysis results were virtually identical for treatments at site one, the sandier site. We did not sample site two at this time as plots were just being established. Postverasion petiole results for both sites did not reveal any differences between treatments. As expected, overall nitrogen levels were lower at the sandier site with the mowing only treatment slightly deficient. Other elements were within normal range or in some cases above normal but levels were comparable across treatments and sites.
Total weed cover results from sites one and two were similar throughout the season. Weed cover was highest for the mowing only plots, intermediate for the single glyphosate and lowest in the two glyphosate treatment. Through most of the season, there was a statistical difference between mowing only and two glyphosate treatment. Weed cover consisted of clover and dandelion early in the season with a predominance of crabgrass by season’s end.
For both sites, there were no statistical differences between berry ripeness or yield components. The two sites had relatively similar Brix (sugar) but the sandier site had a slightly higher pH and a substantially lower titratable acidity compared to the heavier site. This is consistent with the slightly later harvest data and sandier soil. The results indicate that yields, cluster weight, cluster number and berry weight were unaffected by any of the treatments. It is possible that differences in yield components would become evident either after several successive years of the same treatments and/or in a season with other stress factors such as drought. While the 2006 data did not suggest a treatment effect, it would be preliminary to state that under trellis mowing absolutely does not impact vines based on a single year’s data. The trials in this vineyard were not continued as space became available in the research vineyard, allowing more rigorous control of treatments and data collection.
3. Under trellis mowing 2008
Nutrient levels for postveraison petiole samples were virtually identical between treatments. All nutrients fell within the sufficient range though calcium was very slightly deficient throughout. If there are differences to be seen in vine nutrient status because of weed management practices, it would be more likely to occur after several years of a given practice rather than in year one.
The percent total weed cover results suggest that mowing only allowed vegetative ground cover or 80% or greater by early summer. Mow only plots consistently had the highest number as well as highest percent vegetative ground cover. Glyphosate only plots had relatively low populations of weeds and percent ground cover. Mowing with single applications of glyphosate resulted in intermediate levels of weed cover. The majority of weed pressure was due to summer annual grasses, particularly hairy crabgrass. We anticipate that perennials such as dandelion will become established as mow only plots are maintained in future seasons.
In the 08 under trellis mowing experiment, there were no statistical differences in yield components or ripeness of crop. For berry samples, there was no statistical difference between Brix (sugar), titratable acidity, pH and berry weight. Cluster number per vine (expected to be non-significant as we thinned to consistent a cluster number per vine), cluster weight and crop weight per vine were similar between treatments. As with vine nutrient status, any impact of weed management practices on yield and fruit quality are more likely to occur in the next 2-3 years rather than in year one.
Education & Outreach Activities and Participation Summary
1. Alternative Weed Management, talk given at Viticulture 2007 industry meeting, Rochester, NY. Preliminary results presented by Wise based on input from Senesac as part of talk on alternative weed management techniques. 100 people in attendance.
2. Alternative weed management article written for VineBalance website by Wise, Senesac and Dunst. VineBalance is the name of the NY sustainable viticulture program. www.vinebalance.org.
3. Results from all trials published in the LIHREC Annual Report. Available on www.longislandhort.cornell.edu.
4. Field meeting, September 9, 2008, tour/discussion of research plots including the under trellis mowing trial. 10 growers.
5. Project overview w/photo and description of new mower sent as part of research program report to winery and vineyard owners, May, 2008.
6. Results from 2008 under trellis study to be published early 2009 in the Long Island Fruit & Vegetable Update and will be posted on the Long Island Vineyard Manager List Serv.
7. Formal presentations on this work will take place after another year of work with the LIHREC under trellis mowing plots as impacts, if any, will take place in year two and beyond.
1. Practical aspects of using an under trellis mower. The tractor speed must be slow (we averaged 1.3-1.5 mph) to allow maneuvering around protruding trunks, otherwise, they can be nicked by mower blades. Also, a faster ground speed tends to cause the unit to bounce excessively when hitting trunks or vineyard posts, though the unit can be adjusted slightly to reduce this tendency. A faster ground speed also bends over the taller weeds rather than mows them. This unit appears to be too powerful for newly planted vines. Even with staked grow tubes, the mower head was perilously close to snapping baby vines. Three year old vines with stakes had to be carefully driven as an inattentive driver will damage those trunks as well. Based on our experience, this unit is best used on mature vineyards with well established trunks. Replacement trunks (new shoots trained up to replace a dead or unproductive vine trunk) would also need to be avoided.
2. Economic comparison of treatment regimes. This is linked to the number of tractor passes, tractor speed, cost of materials (glyphosate in this case) and/or the use of backpacks for spot treatment rather than tractor application. The wide swings in the cost of pesticides as well as fuel prices make costs highly variable. However, even if a similar number of tractor passes is utilized for each treatment regime, tractor speed for the under trellis mower is slow, increasing costs substantially. Regardless, it is likely that, assuming mowing is not detrimental to vine health and productivity long-term, avoidance of herbicides will motivate some growers to accept an increase in labor and fuel costs. We had insufficient data in 2008 to fully explore an economic analysis.
3. Under trellis living mulches represent an option for under trellis weed management. In our experience, living mulches can be a challenge to establish in an existing vineyard due to compaction, existing weeds, lack of soil preparation and/or persistence of previously used herbicides. In addition to the time and expense of seeding, rogue weeds must be systematically removed through the season. Over the years, many of the groundcovers that we have tested have winter killed including subterranean and dutch white clover. Other covers such as annual bluegrass might be easier to establish but would likely be more competitive. Our attempt to use native species to avoid some of these issues was not successful due to a lack of seed sources. For all of these reasons, this strategy should be pursued only by those willing to invest in maintenance and periodic reseeding of the plots as well as monitoring of vine performance.
4. Under trellis mowing was originally conceived as a means of under trellis weed control for hilly terrain in the western U.S. There is interest in using this technique in the eastern U.S. as an alternative to maintaining the area with herbicides. Under trellis mowing increases labor costs, fuel costs and increases soil compaction due to the increase in tractor use. Preliminary work done in 2008 indicated, as expected, no impact on vine health or yield components. Vine size as determined by vine pruning weight has not been recorded as of this writing. It is likely that any potential impacts on vine health, vine size and yield components such as berry size and berry number per cluster will occur after several years of maintaining plots. Irrigation, which is common in Long Island vineyards, may help to reduce any detrimental impacts of significant weed cover on vine size and/or yield components.
Areas needing additional study
We plan to maintain under trellis mowing plots at the LIHREC research vineyard for a minimum of two more years to gauge the impacts of the treatments through different growing seasons. Differences in heat accumulation and rainfall amount and patterns can profoundly impact how vines grow and how weed control treatments evolve. After several more years of experience, we will be better able to quantify the risks and benefits as well as the cost of mowing as weed control strategy for under the grapevine trellis.