In 2008, California Certified Organic Farmers reported 21,370 acres were certified and dedicated to the production of grapes. This was up from 17,146 acres in 2005. Most of California’s organic grapes are grown in the state’s coastal wine-growing districts, Mendocino County and Napa County. Producing grapes in this Mediterranean-like climate is not considered difficult, and organic grape growers are proving it with high yields of high-quality grapes. However, as you move inland and head East, the climate changes and makes the production of organic grapes a bit challenging. As the amount of rainfall and humidity increases, so does the pressure from pests and diseases. For the sake of space, I’ll put grapevine pests on the back burner and focus this month on fungus-based diseases (black rot, downy mildew, powdery mildew, anthracnose, phomopsis cane and leaf spot, Eutypa dieback and botrytis bunch rot) that are the bane of grape growers in the East.
A number of fungicides are approved for use on certified organic grapes. Copper-based fungicides are among them. You may remember I wrote about apple scab a few months ago (September 2009, www.growingmagazine.com/article.php?id=4001), and how it can be organically controlled with copper, but that copper is increasingly considered toxic, and European countries have either banned it or are in the process of phasing it out. The same applies to the use of copper in vineyards. Copper ions kill fungi and bacteria. At the same time, they harm plants by killing proteins in the plant’s tissues. This is especially the case when they are overused or used in cold, damp climates. If the vegetation does not have a chance to dry out, the ions are more likely to damage that which you are trying to protect. Sulfur-based fungicides are another option. Dilute solutions are allowed for use during the growing season. Dilute because, like copper, it has the capacity to burn the foliage and fruit you spray it on, particularly when temperatures start to soar past 80 degrees F. Some grape cultivars, such as Concord, have been found to be particularly sensitive to sulfur. If it is used late in the growing stage (i.e., while grapes are ripening), it can disrupt fermentation during the wine-making process. On top of all this, there is an ongoing debate in the scientific community as to whether or not sulfur negatively impacts beneficial insect populations.
An increasing number of alternative fungicides have been approved for use on organic vineyards and show great promise in the control of grape diseases. Kaligreen, from Otsuka Chemical Co., is a potassium bicarbonate-based fungicide for use in the control of powdery mildew. Mycostop, from Verdera, contains Streptomyces bacteria that suppress botrytis. AgraQuest, Inc.’s Sonata is based on a strain of Bacillus discovered, developed and patented by the company’s researchers. It aids in the control of downy and powdery mildews and rusts. There are many other products out there; this is just a short list to give you a taste. Remember: organic farming may be as old as the hills, but technological advances are being made in the interests of organic systems. Like it or not.
The organic grape grower ideally starts a vineyard from scratch and plants disease-resistant cultivars suited to his or her growing microclimate. When resistant cultivars are planted and trained in such a way as to maximize airflow and sunlight between rows and among vines, the need for fungicides can be significantly reduced. Not surprisingly, resistant varieties vary from region to region, as grape cultivars typically have a narrow geographic range to which they are suited. Plant one outside of its climatic comfort zone and you’ll be fighting an uphill battle, doubly so if you’re an organic grower. Also, no cultivar is resistant to all disease. At least not yet. So it is important to know what disease(s) plague your area and select cultivars that can withstand them. Fortunately, there are breeding programs scattered across the United States with the goal of developing disease-resistant cultivars suited to specific growing regions. I will mention a few of them here, but there are more. As always, your local Cooperative Extension Service is a wonderful resource when it comes to what cultivars are best suited for you.
Cornell University’s Agricultural Experiment Station in Geneva, N.Y., has been researching grapevines since 1880. Over time it has introduced more than 50 wine and juice grape cultivars suited to New York’s climate and soils. Today, the University’s Grape Breeding Program (www.nysaes.cornell.edu/hort/faculty/reisch/grapeinfo.html#breed) is developing cold-hardy, disease-resistant, high-yield and high-quality cultivars. In 2009 alone, seven cultivars were released: four produce red wine grapes and three produce white wine grapes.
Since the mid-1980s, the University of Minnesota has maintained a breeding program with the goal of producing cold-hardy, disease-resistant, high-quality grape cultivars for the wine and table grape markets (www.grapes.umn.edu). Between 1996 and 2006, university researchers developed four cold-hardy wine grape cultivars. Two, Frontenac (red) and Frontenac gris (white), are particularly noteworthy because they are resistant to downy mildew, moderately resistant to powdery mildew, and produce high yields of medium to large clusters comprised of small berries. Frontenac is currently grown in the Midwest and Northeast, including Quebec.
The University of Arkansas initiated a grape breeding program at the Arkansas Agricultural Experiment Station in 1964 (www.aragriculture.org/horticulture/fruits_nuts/Grapes/). Its goal has been to develop grape cultivars for, among other things, their adaptation to the upper South, Midwest and Eastern United States. In 1993, it released Sunbelt, a juice grape adapted to the United States’ south-central region. It demonstrates moderate to high resistance to black rot, anthracnose and mildews and produces juice equal in quality to that of the Concord grape.
This is but one short chapter in the world of organic grape growing. I haven’t even touched on what to do when the customer wants a grape that doesn’t grow well without regular doses of chemical pesticides. I’ll save that one for later. By the way, if you’re interested in reading a book on this topic, The Grape Grower: A Guide to Organic Viticulture by Lon Rombough will certainly whet your appetite. And mark your calendar: the 10th International Conference on Grapevine Breeding and Genetics will be held in Geneva, N.Y., on August 2-5, 2010.
The author, a monthly contributor to Growing, is a biologist who lives and farms in Vermont’s Northeast Kingdom.