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by Hans Buchler
In recent years organic grape growing particularly for organic wine, has attracted increasing interest from consumers and also from some growers. At present, approximately three percent of the grape acreage in British Columbia is organic; one winery is producing fully 'certified organic' wine and two other wineries produce some wine 'made from organically grown grapes'. At Park Hill Vineyards, near Oliver in the South Okanagan Valley, we grow about seventeen acres of organic wine grapes. One quarter of the acreage is planted to French hybrid varieties (Foch and Verdelet) and the rest are all European vinifera varieties (Chardonnay, Pinot Noir, Gamay, Riesling, Gewuerztraminer and Semillon). All these grapes are at present processed by Mission Hill Winery; some of them are vinified separately and sold as 'Wine made from organic grapes' and the rest are blended with conventional product.
Our soils are a mix of light to medium sandy loam, with some banks of medium to coarse gravel, very low in organic matter, which is rather typical for the semi-arid, virgin benchland in the south Okanagan. For reasons of sustainability, both environmental and economic, we use a soil management program that relies on a minimum of off-farm inputs and requires little maintenance. To this end we have developed a system of mostly self-reseeding biannual cover crops: between late July and mid September we seed inoculated hairy vetch at approximately 20 pounds per acre. We broadcast the seed between the grape rows onto a disked seedbed and cover the seed with a very light disking. Other cover crops such as fall rye, annual ryegrass or other legumes can be mixed in with the vetch. This cover crop germinates in the fall, but will only grow vigorously the next spring. Hairy vetch goes to seed in late June or early July and dries out by the end of July. The dead cover crop will then be mowed in August or before harvest and left as a mulch, allowing the hairy vetch to germinate again, without incorporation of the cover crop residue.
While this technique reduces the amount of nutrients available in the short term, it is more effective in increasing the organic matter content of our soils, because the cover crop residue will not be quickly mineralized, due to excessive cultivation. Rather, the crop residue will be slowly decomposed by all kinds of soil organisms and bound to clay particles, to form stable humus. This system is repeated for three to four years in a row, or until another spontaneous crop displas the hairy vetch, before it will become necessary to cultivate the soil and reseed thecover crop.
Some of the advantages of this cover crop technique are: low cost of input and maintenance; sufficient availability of nutrients for the main crop; low compaction and erosion hazard; good habitat for beneficials (vetch allows a variety of flowering plants to grow later in the season; we sometimes also overseed with buckwheat before the vetch dies); and good improvement of soil filth and organic matter content over the years.
There are of course alsosome drawbacks: hairy vetch can grow extremely fast and invade the grape plants in the rows if left unchecked; it provides shelter from birds of prey for pocket gophers and other small rodents; in some years, especially the year after cultivation and reseeding, hairy vetch can release an excessive amount of nitrogen and cause too much vegetative growth, delaying crop maturity. While potassium and nitrogen levels are stable or increasing I do not yet know what will happen to the levels of phosphates in the long run!
Other legume cover crops with a similar life cycle are: crimson clover, which is attractive, is a good habitat for beneficials, has less organic matter than vetch, and can be displaced by more vigorous plants; and black medic, whose tiny yellow flowers may be too small for many beneficials to feed on, regrows after mowing, displays winter hardiness similar to hairy vetch, and whose seed is difficult to buy. In California and Oregon, many organic vineyards use subterranean clover as their cover crop of choice, but chances are that it would not survive our low winter temperatures.
In order to reduce competition from weed growth, we try to leave about one foot on either side of the grape rows relatively weed-free. This is accomplished through a variety of methods. Young plants are hand weeded around the base and mechanically weeded on the row with a hydraulic grape hoe. Weeds around older plantings are suppressed with a 1iquid propane' torch, the inverted tank carried on a backpack. This is very effective on young freshly germinated annuals, while most perennials eventually recover and regrow, unless it is frequently repeated (small-scale tests this year show that it takes up to seven passes with the propane burner to kill clumps of orchard grass). If perennials become a serious problem, I resort to mechanical or hand removal of weeds.
The major advantage of thermal weed suppression is that after a few years without disturbing the soil, density of weed stands is greatly reduced. The major drawback, apart from the fact that it consumes about twenty-five pounds of propane per acre per pass, is the serious fire hazard. It is extremely important to use propane weeders only when the weeds and cover crop are moist. I only use it during or shortly after rain or irrigation, if possible on cloudy days or in the evening to avoid grass fires! Depending on weed density, two to three passes per year are usually sufficient.
In our area, the prevalent fungal disease is powdery mildew (Unanula necator), which can be a problem with some of the European varieties. There are, however, quite a few control methods available to the organic grower, sulphur being the most frequently used. Some other materials that have been tested at the Summerland Research Station and found to be effective are canola oils, jojoba oil and potassium silicate (related to the active ingredient in horsetail, Equisetum arvense). To achieve good control, the first application must be made shortly after bud break and repeated two to four times, depending on variety.
Unfortunately, none of these materials, except sulphur and copper, are registered under the Pest Control Act; consequently, they are not supposed to be used by growers. This opens a can of worms that is too big to address here. Suffice it to say that, in my opinion, organic growers should launch a unified effort to lobby the federal government for some exemptions from this Act. I have repeatedly broken the law by applying home-made horsetail extract in my vineyard. And, I am sure, so have many other organic growers.
The only other important fungal disease in our area is bunch rot (Botrytis anerea). This problem seems to afflict mostly conventional vineyards and is rarely seen in organically managed sites. The best control, even for conventional growers, is achieved through canopy management, by reducing vigor and opening the fruiting area to air and light.
Probably the biggest challenge fc most organic grape growers in our a is the control of leafhoppers (Virgin). Creeper Leafhopper or Erithrorneura ziczac). In 1990, Matthew Frey, an organic grape grower and winemaker from California who was invited to t Okanagan to make a presentation on organic grapes and wine, was asked what they do in California about leafhoppers. He replied, "We pray." The questioner, who was obviously not satisfied with this response, rephrase the question: "What do you do, if you have a lot of leafhoppers?" Matthew replied, "We pray a lot." At the time, many of us thought this rather strang but in retrospect this approach may be depending on one's point of view, a waste of time but at least it is not a waste of both time and money. And, I must confess, I have certainly done b, in the past years. We used to spray Safeis insecticidal soap, which does kill some of the first instars of the leafhopper nymphs, but timing and full coverage of the underside of the leaves is crucial. To achieve good coverage, we used an old spray gun with an angler. nozzle on a long hose, which gave on occasion satisfactory results. But applications are time-consuming and need be repeated. The soap is also applied at concentrations near phytotoxic levels for grapes (at around 15%), which can occasionally result in some leaf burning; the material itself is also quite costly, putting the overall benefit into questir For three years in a row now, I have released lacewings, at the rate of 20,0C to 30,000 per year per acre, in the hope of reducing the leafhopper populatior While lacewing larvae do eat small leafhopper nymphs, they often seem to move into the cover crop to feed on other insects. The adults rarely lay their eggs on the grape vine, so continuous releases would be necessary to achieve a little control. However, the leafhopper population has decreased in the last two years, not because of the lacewings, as wishful thinking would have me believe, but primarily because of an increasing number of naturally established leafhopper parasites, called Anagrus epos.
This tiny, almost microscopic mymarid wasp lays its eggs in leafhopper eggs, eats the developing leafhopper nymph and emerges as a sexually mature adult, ready to parasitize many more eggs. If this sounds too good to be true, it's because it is: this parasite does not overwinter on the Virginia Creeper Leafhoppers, which go through the winter as adults, but needs other leafhoppers that overwinter in their egg stage to make it through the cold season. But help may be on its way!
The British Columbia Wine Institute is funding a two-year research project which is conducted by Dr. Gary Judd and Dr. Tom Lowery at the Summerland Research Station. This project will study the feasibility of mass rearing of Anagrus, or any other means that allow a release in spring timed with the first oviposition (egglaying) of the Virginia Creeper Leafhopper. It will also look at habitat and possibilities of its enhancement and generally try to learn as much about this parasite as possible. If this approach should prove to be successful, it may-in future be possible to apply this technique to the control of other leafhoppers, such as the Potato Leafhopper. A not-yet-officially confirmed but seemingly effective control may be provided by the European Earwig, which appears to systernatically scratch the leafhopper eggs from the underside of the grape leaves.
The cutworm, which can completely defoliate young plants in spring, is another major insect pest, especially in newly planted vineyards. This seems to be more of a problem in newly converted plantings than in plantings under long-term organic management. While Bacillus thuringiensis is effective against cutworms, it is not registered for use on grapes, so many growers resort to digging for cutworms at the base of young plants, under soil or debris. Lately our cutworm problem seems to be under control, maybe thanks to a growing number of toads that spend the day buried under the soil.
Overall, with time, many pests seem to become less of a problem under organic management. There are of course many exceptions to this, such as the bears who seem to come with family and friends to hold grape munching socials, and the pocket gophers, birds, deer, raccoons and other creatures who all show up at harvest time to get their share.
Hans Buchler and his wife Christine came to the Okanagan in 1981 from Switzerland, where they operated an organic market garden. They planted grapes in 1983 and became members of SOOPA (Similkameen Okanagan Organic Producers Association) in 1990. Hans has been a member of the board of SOOPA for many years and is past president of the COABC (Certified Organic Associations of B.C.)
Copyright © 1997. Hans Buchler.
Reprinted with permission. All rights reserved.
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