You may have noticed rose plants adorning the rows of pristine vineyards on your last tour of wine country, and you probably were never intrigued by the roses except to admire their beauty. Although roses do add a touch of elegance to reflect the vineyardist’s attention to aesthetics, rose plants play a much more practical and functional role in viticulture (the science and practices of planting, managing and training vines, and growing grapes).
Planting roses at the end of vineyard rows is a simple and effective trick-what some call a miner’s canary-as an early warning sign of an impending disease, usually powdery mildew or downy mildew because roses are more sensitive than grapevines. If either disease sets in, the vineyardist then sprays the vineyard with appropriate fungicides. Those who routinely include fungicides in their vineyard management practices do not need to plant roses.
Powdery mildew, also known as Oidium, is a disease triggered by the fungus Uncinula necator (or Erysiphe necator) that causes white powder-like spots on vine leaves and grapes during the growing season, particularly in microclimates of high humidity and temperatures and shade. If the fungus attacks berries, grapes can take on strong earthy (1-octen-3-one) and geranium-like [(Z)-1,5-octadien-3-one] smells, and can split and open and become prone to other diseases. But according to the Journal of Agricultural and Food Chemistry, research conducted at the Faculté d’Œnologie of the Université Victor Segalen Bordeaux in France demonstrated that delicate wine aromas were much attenuated as the compounds are enzymatically reduced by S. cerevisiae wine yeast during alcoholic fermentation. Powdery mildew can be easily prevented with a sulfur spray once (if) signs of the disease appear on the roses.
Downy mildew is a much more serious disease that is triggered by the mold Plasmopara viticola which thrives in more humid and persistently wet conditions. It causes “oily spots” on leaves or greasy yellowish spots that turn a brownish color. Infected leaves and affected grapes eventually drop from vines, which not only result in spoiled grapes and lost crop, but can survive the winter and once again spread the disease the following spring when the vineyard cycle restarts. Downy mildew can be prevented with a copper sulfate spray solution once, and if, signs of the disease appear on the roses.
As if the risks of running a vineyard weren’t high enough, they can be greatly reduced by an ounce of prevention.