In the spring of 1980 I was walking through a research vineyard on the property of the University of California at Davis. At the time I was a graduate student in the department of Plant Pathology, studying the diseases of plants. I worked in the lab of Dr. Mary Ann Sall who had responsibility to do research on the diseases of grapes – a very important crop in California and the crop that was my introduction to agriculture. That particular morning the grapes happened to be in bloom. Bloom time in grapes is not very dramatic. Grapes don’t have any petals on their flowers since they don’t need to attract pollinators. They simply self-pollinate in the process of the flower opening or with a little wind.
|Grape blossoms look like this (Image via Pixabay)|
However, what struck me on that spring morning was that there was a very pleasant fragrance wafting around in that vineyard. Since this was my fourth season of being in vineyards during bloom I wondered why I had never “smelled the flowers” before. Then I realized what was going on. This particular vineyard had not been dusted or sprayed with sulfur, the normal protection against a disease called powdery mildew. Instead my boss was using these vines to test a brand new fungicide called Bayleton. Bayleton is a synthetic chemical that affects an enzyme in a pathway that exists in fungi, but not in plants or animals (Triazole fungicides, effecting Ergosterol Biosynthesis). Dr. Sall was testing it as a new alternative to protect grapes from one of their most troublesome pests – a fungal disease called powdery mildew. Because of this new alternative to sulfur, I was able to experience a floral fragrance that was different from all my other spring, vineyard experiences.
|Young grape berries infected with powdery mildew (Wikipedia Commons)|
Grapes grown in a dry, Mediterranean climate like California are spared some of the most problematic diseases that occur in rainier places like France and Germany. However, the powdery mildew fungus can infect even without any rain. If you have grown roses you have probably seen the type of powdery mildew that attacks that garden favorite, and there are powdery mildews specific to a great many other wild and cultivated plants.
Probably since ancient times, people have known that you can prevent powdery mildew damage on grapes by dusting them with the element, sulfur. Sulfur, which can be mined, is considered to be a “natural product” and thus it is approved for use in organic. Both conventional and organic farmers use a great deal of sulfur – it is by far the most widely used pesticide in California and particularly for grapes. Back in 1980 is was common for vineyards to be dusted with 6-10 pounds per acre of sulfur as frequently as every 7-10 days from the time the grapes start growing until they begin to ripen. The sulfur was necessary to prevent mildew infections, which are very bad for wine quality or for the quality of table grapes or raisin grapes.
Even though the sulfur is “natural” and good for controlling both mildew and spider mites, it isn’t a pleasant thing to be around when you are out working in a vineyard. It is irritating to one’s eyes and skin. I always had to keep my vineyard clothes separate from all the other laundry or it would all end up smelling like sulfur.
Back to the new fungicide – it turned out that with Bayleton, grapes growers could control mildew using a far lower dose than sulfur and do so only once every three weeks, not every week. When the product became available, it was enthusiastically adopted by the grape growers as a far better option than sulfur. Unfortunately the switch was too popular and in time strains of grape powdery mildew arose which were resistant to that fungicide. Fortunately newer compounds in the same “chemical family” were developed which overcame that issue, and in subsequent years several other good mildew fungicides have been developed with a different “mode of action.” Sulfur is now playing a much smaller role in modern, “integrated pest management” programs in grapes that rotate different kinds of products through the season so that the fungus doesn’t become resistant to any of them.
|Note that that most dramatic trend in modern grape pesticide use is that far less sulfur is being applied|
All of these changes have been quite positive for grape quality, farm worker (and graduate student) comfort, and for the environment since much less fuel is used for applications than it was back in the day when sulfur was the only option. That rare chance I had to smell the grape flowers back in 1980 still resonates with me as a symbol of the steady progress in pest management throughout my career. The next time that you are enjoying a nice wine, you might also raise a glass to this example of progress in the art of crop protection.