Under trellis cover crop trial – 2013 Summary
A.Wise CCE-SC

This is the second installment of an article on research being conducted on management of the area under the vine row, or just beneath the vines. In the previous article we discussed mowing the existing vegetation that grew there naturally. In this article we will discuss the results of work done when we direct seed a ground cover beneath the vines. This block of seeded covers has been maintained since 2011. There are four treatments: T1 - glyphosate only (2x); T2 - Dutch white clover; T3 - No Mow fescue mix; and T4 - a combination of clover and No Mow, all seeded in spring, 2011.  By year two, the clover dominated the no mow in T4. However, in 2013, clover in both T2 and T4 was not as robust, took a long time to establish and gave the no mow a chance to recover in the T4 plots and weeds a chance to break through in the T2 plots.

As in previous years, there were no significant differences in shoot length or in shoot diameter (Table 1). The six central vines in each plot were pruned on December 11 and prunings (previous season’s shoots) were weighed. Vines in no mow plots (T3) were substantially smaller than clover (T2) or glyphosate plots (T1) (Table 2). This was visually evident during the growing season. We believe this is due to diminished shoot growth later in the season as well as a reduction in the number and length of lateral shoots (green shoots arising from the leaf axil of a primary shoot). It is difficult to capture data on lateral shoots due to repeated trimming of the canopy in VSP training systems used on Long Island. Pruning weights in the clover and herbicide plots were similar

In petiole analyses, vines in both clover plots had significantly higher levels of petiole N on July 2 than the No Mow plots. (See the full report on our website: http://ccesuffolk.org/viticulture for this data). The vines with No Mow as cover were visually nitrogen deficient and water stressed. The two treatments with clover had lower levels of phosphorous and calcium. Clover is a heavy Phosphorus feeder and additions are often recommended when establishing it as a forage crop. Soil analyses were similar among treatments (data not presented).

We have not been able to confirm any impact of cover crops on ripening or yield components (Table 3). We had theorized that competition provided by cover crops would reduce berries/cluster (reducing susceptibility to cluster rot) and/or berry weight (improved fruit quality due to a higher skin:flesh ratio).

In order to assess nitrate leaching, lysimeters were installed in April, 2013. As discussed in the previous article, the lysimeters are devices for collecting water in order to determine the soluble constituents in water. We later extract this water and analyze them for nitrates. Results suggest that clover plots released more nitrogen; however, the erratic performance of the lysimeters due to the lack of rain in the 2013 growing season precluded data analysis that might verify this (Table 4). We will continue to take data using the lysimeters in the upcoming season.

There are several interesting trends coming out of this work. As discussed in the first paragraph even though the clover established well in the first and second season by the third season the clover was slow to reestablish in the spring. This gave No Mow time to spread but also allowed weeds to establish themselves. In our research block and several grower blocks the clover increased petiole nitrogen compared to the No Mow and increased vine size based on pruning weights (Table 2). Unless the grower is looking for more nitrogen this could be a problem. Vice versa is true for the No Mow where we saw a reduction in petiole N and vine size. From these initial results we encourage growers to try a block or a few rows on their own. Utilizing clover for drier sites with smaller vines where they may need more nitrogen and No Mow for heavier soils and/or larger vines. We will continue this work through the 2014 season and are also investigating a variety of other seeded ground covers.

For more information, as well more other tables see the full report on our website: http://ccesuffolk.org/viticulture.

Table 1. Under trellis cover crop trial: vine growth measurements, cv. Syrah

Treatments		2012 season				2013 season
		Shoot length-cm -5.16	Shoot length 5.29	Shoot length 6.11	Shoot diameter cm - 8.6	Shoot length 6.4	Shoot length 6.10	Shoot length 6.14	Shoot diameter 8.12
T1	Glyphosate 2x	19.6	56.8	91.0	9.2	50.5	63.4	72.3	9.6
T2	Clover	19.3	55.5	90.8	9.1	52.5	67.1	74.5	9.9
T3	No mow fescue	19.7	54.8	89.8	8.9	53.5	64.8	72.2	9.3
T4	Clover +no mow	19.9	58.9	91.4	9.0	53.3	8.1	76.3	9.8
Significance1		ns	ns	ns	ns	ns	ns	ns	ns

1 – Values followed by the same letter are not significantly different, p=0.05. ns – no significant difference.

Table 2. Under trellis cover crop trial: vine pruning weights, cv. Syrah

Treatments		2012 season		2013 season
		Vine pruning wt. lbs - 12.6.12	Vine pruning wt. lbs./foot of row	Vine pruning wt. lbs - 12.11.13	Vine pruning wt. lbs./foot of row
T1	Glyphosate 2x	1.76	0.44	1.72 a	0.43
T2	Clover	1.80	0.45	1.82 a	0.46
T3	No mow fescue	1.39	0.35	1.39 b	0.35
T4	Clover +no mow	1.76	0.44	1.61ab	0.40
Significance1		ns	--	0.0142	--

1 – Values followed by the same letter are not significantly different, p=0.05. ns – no significant difference.

Table 3. Under trellis cover crop trial: fruit ripeness and yield components, cv. Syrah, 10.5.13

		Brix	TA g/l	pH	Berry wt. - g	Berry no./clust	Clust no/vine	Crop wt/ vine-lbs.	Avg clust wt-lbs.
T1	Glyphosate 2x	20.8	6.8	3.61	2.3	64.2	15.8	4.0	0.24
T2	Clover only	20.6	7.1	3.57	2.4	65.5	17.3	4.1	0.23
T3	No mow	20.4	6.7	3.59	2.3	67.0	17.6	4.4	0.24
T4	Clover + no mow	20.6	6.9	3.60	2.3	69.6	18.6	4.9	0.25
Significance1		ns	ns	ns	ns	ns	ns	ns	ns

1 – Values followed by the same letter are not significantly different at p=0.05; ns – no significant difference.

Table 4. Under trellis cover crop trial, ppm nitrate-nitrogen from lysimeter samples, cv. Syrah, 2013

Treatment		5.13.13	5.21.13	6.5.13	6.11.13	7.2.13
T.1	Glyphosate 2x	0.14	0.19	0.63	0.96	0.48
T.2	Clover	1.08	0.80	2.25	1.30	4.44
T.3	No mow	0.17	0.17	0.24	0.22	1.66
T.4	Clover + no mow	0.76	0.76	0.60	2.31	***
% of lysimeters providing a sample		55%	60%	80%	100%	20%

*** None of the five lysimeters provided a sample.

Each treatment had five lysimeters. These numbers represent averages though not all lysimeters yielded samples on 4 of 5 dates. Unsuccessful attempts to sample lysimeters - 6/24, 7/23, 7/30, 8/22, 8/30.