Friday, September 9, 2011

VITICULTURE: Deciding on Nature's Variable

Growing grapes on the vine should be easy, but I've just had to dust my few ornamental vitis vinifera vines once again for the fungal powdery mildew, odium. Above average seasonal rainfall in our Winter was a good start this year, but it inhibited bud break as temperatures rose above 50 degrees, and flowering as it continued throughout the wet Spring. The self-pollinating fruit set that followed was spotty(shatter or coulure), as cooler temperatures combined with late rains; and when the growing season that is Summer finally started, it remained so cool that the stagnant fruit growth had berries of different sizes(millerandage). Finally, the color-change that indicates sugars translocation from leaves to berries, verasion, occurred here in late-July & August, but local growers expect that the cooler ripening conditions will result in a smaller annual harvest about two to three weeks later than usual. Growers now recognize that beyond the targeted threshold of developing grape sugars(ripeness), physiological maturity of the berry and its pulp, including its pips(tannin) and other phenolics are increasingly important for great fruit. Such is the life of the farmer.
Immature grape vine berries
Great wines are made in the vineyard, it is said, so wine consumers are quite fortunate that there is a science dedicated to growing the best grapes on the most appropriate vineyards sites: viticulture. This field science has evolved for more than a hundred years, from its origins in the great generation of agricultural science that was the late 19th century. Vitis Vinifera, the wild family of old world winegrapes, whose origins may be in the Caucasus' or Southwestern Asia, was found to grow best in between temperate latitudes of 30 to 50 degrees latitude(North & South). Across the globe, the perennial grapevine has propagated to Mediterranean, Continental and Maritime climates with not much less than an average 57 degree temperature; adapting to harsher vineyard environments when moderated by a significant bodies of water, like a river or lake. Grapevines can grow in a wide range of soil types: chalk to limestone, slate to loess soils, calcareous marls to sedimentary clays, but do best in well-drained high pH compositions. The vine only requires three major nutrients: nitrogen(N), phosphorus(P) and potassium(K), with a collection of minor nutrients including iron(Fe), manganese(Mn) and magnesium(Mg).
Sangiovese at Verasion

It has been determined that the vine requires a minimum of about 27 inches annual rainfall, mostly during its dormant period, and that irrigation can benefit the vine in the heat of its warmest stress periods. Further, a minimum of about 1500 sunshine hours annually are required during the vines growing season, with an average respective temperature of between 66 to 70 F degrees for white or red varietals to ripen.  A suitable growing regions Heat Accumulation can be measured by degree days. Locally the mean number of days over 50 degrees F is calculated by the California Summation Heat Index, where Region I is less than 2500 days F and ranging to over 4000 degree days F of Region V. My warm coastal vineyard's mesoclimate environment is in Region II.

Vine trellising for support and dormant season pruning are part of canopy management, combining to afford the vineyard manager important tools for achieving the goal of balanced growth. A principal of Australian enologist, Dr. Richard Smart, a balanced vineyard finds the relationship between the soil/root system and the total number of potential leaves it can characteristically maintain. Vitis Vinifera can be head-trained, which are either spur-pruned or cane pruned, or cordon-trained, which are exclusively spur pruned. Simplest form of spur-pruning is the ancient, unsupported Goblet system, which is used widely in the Southern Rhone. A basic type of cane-pruning is the Guyot system, developed in the 1860's by Dr. Jules Guyot, and is used widely in Bordeaux. Today, a vineyard manager has literally dozens of training systems from which to choose, ultimately to control vine vigor and to optimize the quality of fruit which it produces.

Cane pruned Medoc vineyard

Conventional, Sustainable or Bio-dynamic?
Increasingly, our local vineyards are employing poly-cultures or sustainable agricultural practices as a part of their ecological canopy management system. Integrated bio-dynamic agriculture, as promoted by Austrian Dr. Rudolf Steiner, was one of the first modern ecological, self-sustaining farming systems and continues to have its global practitioners more than eighty years after Steiner's passing.  Farming choices also include a vineyards propagation by either a nursery clonal selection or mass selection(selection massale), where a vineyard mass budwood selection is intended to reinforce positive traits of a vineyards favored vines.Once selected, the scion is grafted on to a separate rootstock, which may have been chosen for its tolerance to drought or for is resistance to the many vineyard diseases, such as the devastating vineyard louse phylloxera.

Vine diseases and pests are a constant threat in any vineyard, whether they be viral, such as the nematode soil pest spread Fan Leaf, or a native fungal malady, like the copper sulfate treated Downy Mildew(peronospera). Not all fungus is undesirable, however, as Botrytis creates a fruit bunch rot in humid conditions which is the "noble rot" producing some of the world's richest dessert wines. Bacteriological afflictions, like the currently fought scourge of Pierces Disease, continues to expand across the U.S. from leafhoppers. Insect infestations and other vineyard pests keep vineyard managers ever vigilant.

Extreme climate changes, such as high winds, hard frosts and hail, especially during flowering or harvest create even more natural challenges for the hard-working viticulturalist. The precise management of each different vineyard environment, understanding its changes and variables, is what the science of viticulture is all about.  With proper practice and maintenance the very best possible reward is produced in a healthy, balanced fruit yield each harvest season. To manage a healthy canopy, to control the vineyards yields, and to preserve its environment create a contemporary working legacy for each viticulturalist. Daily, they must decide on the variables of Nature.
Bulgarian Vineyard harvest

This is a good reminder to look again at my vine experiment. With a quick look to the garden's grapevine curtain outside, and I see that the birds have already eaten my ripest grape clusters.  I guess the farmer's mantra should be 'there is always next year'. Cheers!

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