NOVEMBER 9, 2017. BY STAN GRANT, VITICULTURIST.
Vineyards are long-term investments expected to annually generate profitable yields of high quality winegrapes over many years (Fig. 1). Unfortunately, too often this expectation is not fulfilled. There are three common reasons for shortened profitable vineyard lives: canker disease, declining root zone function, and chronic vine growth imbalance. In this article, we will consider these reasons and examine ways to lengthen the useful lives of vineyards.
Canker diseases affect most vineyards because, unfortunately, most winegrape varieties are susceptible to them. Fungi causing canker disease infect wounds and slowly penetrate into cordons and trunks, leaving dead wood behind. Without a concerted effort, infections become obvious as dead spurs when vineyards are about 10 years old. Fruit yields typically begin to decline a few years later (Fig. 2). At first, the yield decline is slow, but it accelerates significantly after vineyards are about 15 years old.
Declining root zone function.
Just as prevalent is the diminishing capacity of vineyard soils to function as grapevine root zones. Without management diligence, soil acidity increases, mineral nutrient availability decreases, and permeability to air, water, and roots lessens over time. Accordingly, vine growth vigor, fruitfulness, and ripening capacity declines, while vine susceptibility to stresses and pests increases. Usually, root zone deterioration occurs more rapidly in parts of vineyards where soils are sandiest and contain the least organic matter. Such differential soil decline increases vine growth and fruit development variability within vineyards, which further compromises their performance and complicates their management (Fig. 3).
Chronic vine growth imbalance.
Recurring imbalances between canopy (vegetative) and fruit (reproductive) growth is also harmful. Excessive canopy development (> 20 nodes/shoot) is associated with rapid shoot growth, intense fruit zone shading, and poorly formed stems. When these conditions are recurrent, low bud fruitfulness and spur loss to winterkill decrease long-term prospects for vineyards. At the other extreme, where canopies are restricted (< 12 nodes/shoot), carbohydrate production is insufficient for ripening and storage requirements. Repeated restricted growth episodes (Fig. 4) quickly lead to spur dieback, vine decline, and sometimes, vine death. Such overcropped vines have very low tolerances for pests, diseases, and mineral nutrient deficiencies.
Given these challenges, how can we sustain productive vineyard lives? Begin by taking a few steps back and taking a broad view of your vineyard and your long-term goal for it. With few exceptions, the long-term vineyard goal is a limitless lifetime of consistently profitable fruit yields. Achieving this goal depends upon vineyard design, development, and management.
Planning new vineyards typically begins with the choice of a winegrape variety. For a long vineyard life, the design also requires careful assessment of the site, especially climate, soil, and irrigation water quantity and quality. The next step in the design process is the selection of a rootstock appropriate for the variety, soil, and irrigation water. These plant and site factors affect final mature vine size and shoot bearing capacity, which are critical to the final step of vineyard design: choosing a spacing-training-trellis-pruning system that will promote vine growth balance with minimum management effort.
To develop a vineyard for the long-term, begin with proper soil amending, deep cultivation, drainage improvements, and installation of a well designed, high performance drip irrigation system. Plan ahead so that you purchase only high-quality, CDFA certified plant material. Plant vines at an appropriate depth with graft unions well above the soil surface and roots are properly oriented. After newly planted vines begin to grow, irrigate, fertilize, and train them to avoid stress and promote the development of well-formed, well-nourished trunks, cordons, and spurs. Confirm vines have ample exposed leaves (≥ 14 to 16 nodes) before allowing them to carry their first crop to avoid overcropping and vine decline.
After vines are fully established, develop an annual vineyard management plan to serve as your guide for consistent year-to-year monitoring and management activities. The viticultural goals of the annual management plan ought to include moderate growth vigor, balanced fruit and foliage growth, fruit zone exposure to air movement and dappled sunlight, balanced vine mineral nutrition, sustained moderate vine water stress, and controlled pests and diseases. These goals assume regular additions of organic matter, mineral amendments and fertilizers, and other inputs as needed to maintain maximum root zone fertility and tilth. They also imply canker disease control measures, such as late pruning, double pruning, pruning wound protection, and if required, surgery to remove and destroy infected vine wood and retraining to replace it.
To conclude, vineyards are long-term investments and in recent years, the value of older vineyards has increased as the wine industry has grown to appreciate old vines. But to attain old vines, we have to design, develop, and consistently manage our vineyards for longevity regardless of winegrape market conditions. Integrated into these activities are efforts to control canker diseases, maintain favorable root zones, and ensure balanced fruit and canopy growth.
A version of this article was originally published in the Mid Valley Agricultural Services March, 2015 newsletter. The article was updated for this blog post.
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