The Need to Improve Vine Size in Northeast Vineyards

Grape production in Northeast vineyards is directly related to vegetative growth until the point at which light interception is maximized. Viticulturists and grape growers measure vegetative growth through dormant cane pruning weight, typically recorded as pounds of pruning per vine or per foot of row (Winkler et al., 1974; Jordan et al., 1980). Although 'pruning weight' or 'vine size' is measured in the winter, it is an estimate of leaf area grown during the previous growing season. A vine that averages low pruning weight has less leaf area and intercepts less sunlight than a larger vine with more leaf area and higher pruning weight. Therefore, greater vine size leads to higher total canopy photosynthesis and greater potential fruit production. However, when vine size is too large, leaf area overfills the allotted trellis space, creates shading within the canopy, and decreases quality production (Shaulis, Amberg and Crowe, 1966).

Research at the Cornell Vineyard Laboratory in Fredonia shows that maximum sustainable Concord production of standard vines (ownrooted, high wire cordon, single trellis wire, 8 foot spacing in the row, 9 feet between rows) is achieved by maintaining approximately 2.5 to 3.0 pounds of pruning weight (Shaulis and Steel, 1969). Under these standard pruning, training, and spacing practices, Concord vines with 2.5 pounds of pruning weight produce enough leaf area to fill the allotted trellis space and ripen approximately 10 tons per acre fruit (figure 1).

Figure 1. Relationship between vine size and yield in a mature Concord vineyard at the Cornell Vineyard Lab in Fredonia, NY. The dot on the curve represents the current industry yield average for the Lake Erie Regional Grape Program.

From 0 to 3 pounds of pruning weight per vine, vegetative growth (trellis fill) is the limitation to light interception and maximum fruit production in Concord vineyards. In vineyards with over 3 pounds of pruning weight per vine, trellis space is the limiting factor to light interception and vineyard production. So where do most of the commercial vineyards in the Northeast fall in terms of vine size and yield? The Concord yield average for the Lake Erie Regional Grape Belt is approximately 5.5 tons/acre. Figure 1 indicates that average industry vine size is approximately 1 pound per vine, well below the target of 2.5 pounds. Vine size is generally recognized as the number one limitation to maximum production in the Lake Erie Grape Belt.

Total solar radiation reaching the vineyards over the growing season in the Northeast is less than that of other major grape growing regions in the states of Washington and California and solar radiation is often referred to as a major limitation to fruit production in the Northeast. However, these data indicate that significant improvements in Northeast vineyard production can be achieved by increasing vine size and intercepting the light that does reach the vineyard and not by increasing sunlight itself (a physical impossibility).

In the late 1950's, Dr. Nelson Shaulis planted a factorial experiment at the Cornell Vineyard Lab in Fredonia known as the "West Tier" experiment. The treatments in the trial include pruning severity, training, shoot positioning, floor management, nitrogen fertilization, and rootstocks -- 96 treatment combinations in all (Shaulis and Steel, 1969). On the subject of root biology, the results show that viticultural practices that stimulate root growth and activity increase vine size and productivity, while inhibiting root activity can be a management tool for controlling excessive vigor. Just about every vineyard management decision directly or indirectly impacts grape roots. Pre-plant decisions such as soil type, depth, and drainage establish rooting potential. Vineyard activities such as weed control, fertilization, and irrigation have direct effects on grapevine roots through water and nutrient availability. Furthermore, canopy and crop management have indirect impacts on root growth and function through carbohydrate assimilation and partitioning.

In the West Tier factorial, a significant increase in vine size and a 3 to 4 ton/acre yield increase is measured through simple weed control (light cultivation) and fertilization (50 pounds actual nitrogen per year). However, most commercial juice grape vineyards are under more restrictive or simply different soil conditions than the Cornell Vineyard Lab. Vine size (or root biology) limitations with respect to water, nutrient, disease, and pest stress on different sites may require different management than cultivation and nitrogen. To address this, current root management projects at the Cornell Vineyard Lab investigate the response of Concord grapevines to nitrogen fertilization, irrigation and pruning, weed management, phylloxera and crop load, rootstocks and soil type, and soil pH.

Several floor management studies have been conducted in at the Cornell Vineyard Lab and in New York Concord vineyards that address vine size and yield. Improvement of soil moisture and grapevine water relations through weed suppression has been the common theme among the different research projects. Other aspects of root growth, root pathogens, or vine nutrition have not been thoroughly investigated.

The competitive effects of permanent sod row middles on Concord productivity are well known (Shaulis and Steel, 1969). However, the deleterious effects of long-term cultivation are also recognized (Wander, 1946). These include an increased risk of erosion, decreased soil organic matter, and reduced soil permeability. In the mid-1950's, researchers recommended a system of incomplete or "trashy" cultivation in which partial weed cover was maintained at all times on non- or moderately erodable sites (Fleming and Alderfer, 1956). Trashy cultivation achieved near maximum productivity while reducing soil and water losses from runoff and the gradual decline in organic matter from continuous cultivation. For highly eroded sites, the recommended practice was to establish a sod for two or three years followed by several years of cultivation, a compromise that reduced productivity during established sod years but conserved soil resources.

No-tillage has replaced cultivation as the predominant method of vineyard floor management in New York vineyards. In two studies conducted in the mid-1980's, vine size, yield, and juice soluble solids were similar for vines receiving either three or four annual cultivations or a single application of glyphosate (Roundup®) herbicide in the row middles (Pool, Dunst and Lakso, 1990; Pool et al., 1995). Besides reducing the risk of erosion, the no-till approach also allows for better equipment access during wet seasons which can be important for timely fungicide applications or harvest.

Cover crops are often touted as an organic alternative to cultivation or herbicides for vineyard row middle management. Legume cover crops have also been suggested for their value in fixing nitrogen and buffering nitrogen release into the soil. These questions were addressed in a floor management experiment conducted in a mature Concord vineyard at the Vineyard Lab in Fredonia from 1991 to 1994 (Pool, Lakso et al., 1995; Pool et al., Unpublished Data). Treatments included mulch, bloom herbicide, cultivation, mowed and unmowed orchard grass, Kentucky bluegrass, crown vetch, white clover, annual ryegrass, and annual ryegrass killed with herbicide at bloom. Vine size was lowest in treatments with living covers after grape bloom and the vine size reducing effect of the covers was greater during drier seasons. All living covers, regardless of species, depressed vine size and did not contribute to higher grapevine tissue nutrient concentrations. Mulch and killed rye treatments had the largest vine size and yield. The mulch treatment consisted of annual applications of straw at 5 tons per acre. The killed rye treatment consisted of annual rye drilled in August (10 lbs. per acre) and killed with glyphosate at bloom. The allelopathic effect of rye decomposition substantially reduced weed germination and subsequent growth between grape bloom and re-seeding.

These research results indicate that actively growing covers, particularly during the post-bloom period, are too competitive with ownrooted Concord in New York, and depress vine size and yield. Eliminating weeds and extending the weed-free period increases grapevine productivity primarily through vine water relations. It is also interesting to note that in a separate experiment, supplemental irrigation could not overcome the competitive effect of sod (Lakso, 1998). Eliminating weeds is better than trying to overcome their competition for water. In conclusion, mulch and killed rye treatments have been shown to maximize vineyard weed suppression, both spatially and temporally, leading to improved grapevine water relations and greater vineyard productivity.

We predict that compost will provide similar weed suppression and water relation benefits as straw mulch at an appropriate application rate. However, the secondary benefits of compost on vine nutrition and pathogen suppression is less understood and may also be significant.

Nitrogen:
Long-term nitrogen fertilization research in New York that compares fertilizer rates of 0, 50, and 100 pounds of actual nitrogen per year shows that Concord grapevines on gravel soil types with relatively low organic matter benefit from the application of 50 pounds of actual nitrogen per year. There is little to no benefit of increasing the fertilizer rate to 100 pounds of nitrogen (Shaulis and Steel, 1969). Despite this information, the industry standard remains at 100 pounds of actual nitrogen per year because nitrogen fertilizer sources are relatively inexpensive and area growers have not yet been faced with water quality issues from excess nitrogen runoff. Current nitrogen fertilizer research in a NY Concord grower vineyard on a heavy silt/loam soil type compares 20, 70, and 120 pounds of actual nitrogen per year. After four years of the experiment, there has been no treatment difference in vine size, yield, juice quality or plant tissue nitrogen concentration (P. Throop, personal communication). Therefore, if compost can provide a buffered supplemental supply of nitrogen, it has the potential of eliminating conventional nitrogen fertilization in Northeast vineyards. Although this may have little impact on the cost of production for grape growers, it may have a large impact on environmental polution issues in the future.

Phosphorus:
Many of the vineyards in New York and Pennsylvania have a shalestone base with low soil pH (3.5-5.5) (Feuer, Garman and Cline, 1955). Aluminum in these acidic soils precipitates with phosphorus making phosphorus unavailable for root uptake and inhibits root growth (Marschner, 1986). Current research at the Cornell vineyard lab investigates the response of Concord grapevines to soil pH. Results indicate that minor changes in soil pH from a pH of 4.5 to a pH of 5.5 greatly increases the vegetative growth and phosphorus nutrition of Concord grapevines (Bates, 1999). In addition to directly providing phosphorus to the vines, the pH buffering capacity of organic compost may benefit Northeast vineyards through soil pH adjustment.

Potassium, Calcium, and Magnesium:
Potassium (K), calcium (Ca), and magnesium (Mg) are similar in that they exist as positively charged ions (cations) in the soil solution and can compete with each other in the soil solution or in root uptake (Marschner, 1986). From a vineyard management perspective, balancing these nutrients is one of the most difficult tasks for a grower. Concord fruit has a high K requirement and K availability is dependent on soil moisture. In years with a big crop and dry weather, foliar potassium deficiency symptoms are observed. In wet years with a low crop, excessive K availability and uptake with low vine K demand leads to foliar Mg deficiency symptoms (Shaulis, 1954; Shaulis, 1961). In the previously mentioned experiment comparing sod, mulch, cultivation, and herbicide treatments, mulched vines had higher potassium and lower magnesium status than the other treatments because of nutrient release from organic matter decomposition and higher soil moisture (Pool, Lakso et al., 1995). In a separate study on organic grape production, organic chicken manure provided excessive Mg to Concord grapevines and induced K deficiency (Peterson, 1995). The nutrient composition of selected compost and the interaction of soil moisture with K, Ca, and Mg nutrition in Northeast vineyards needs further investigation.

In other grape growing regions, the best IPM solution for below ground vineyard limitations such as water availability, phylloxera, nematodes, soil pH, and fertility has been rootstock selection (Mullins, Bouquet and Williams, 1992). Although rootstocks may be the answer for some new vineyards in the Northeast, it will not be the solution for existing vineyards. The majority of the grape production in the Northeast is in the Lake Erie Grape Belt which is dominated by the Concord juice industry. Almost all of the Concord vineyards are ownrooted vines and it is common for vineyards to be 30 years old or older. The economics of the industry does not make replanting on a new rootstock a feasible solution; therefore, other IPM solutions such as mulch or compost have a greater chance of being accepted and implemented by Northeast grape growers and have a potentialy higher impact on industry productivity as a whole.

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