When you are a wine grower in the Finger Lakes, you have your share of challenges. Being situated in a cool climate means you have a short growth season, with grapes struggling to fully ripen in some vintages. A mild winter could spur an early bud break, but the prospect of a longer season could be dashed by a late-spring frost event that kills the bulk of the fragile young buds.
That’s just the weather. You also have to deal with a host of harmful organisms such as insects like Japanese beetles, grape berry moths and the looming spotted lanternfly; viruses with names of leafroll, fanleaf and redblotch (yes, grapevines get infected by viruses just like humans); and don’t forget “bigger” threats such as deer, rodents and birds which can eat up your source of income in short order.
Then there are the fungal diseases. Vinifera grapevines are particularly vulnerable to them since Vitis vinifera originated in Europe, while the local fungi are proudly American. The vines have not had the time to develop evolutionary adaptations to combat those fungal pathogens.
The fungus (Erysiphe necator) causing powdery mildew attacks pretty much all farm products. It does not require free water to flourish. In other words, no rain is needed, just high humidity and moderate temperatures — conditions familiar to the Finger Lakes.
“Conifers are the only plant group that is not affected by powdery mildew,” said David Gadoury, a plant pathologist at Cornell’s AgriTech campus in Geneva.
To defend their vineyards, growers subscribe to a fungicide spraying program, commencing in the early spring when grapevines are particularly vulnerable. The applications could number 10 to 15 per year. But as organic farming becomes more and more desirable, growers are trying to find ways to minimize the use of chemicals.
Gadoury and a multi-national team have been working on a solution to use UV light to combat fungal diseases in agriculture. UV light has been used to kill germs for decades in hospitals and laboratories. And Cornell has been researching its effect on powdery mildew since 1991.
“It worked, but it also damaged the grapevines. We were applying high-dosage treatments during daytime,” Gadoury said, describing those early researches.
The dosage was high because the fungus has evolved a way to repair its cells from low-level UV damage.
“UV light messes up two DNA base pairs of the fungus and fuses them together. But then its biochemical defense mechanism kicks in and snips them free again,” Gadoury explained. “It was until almost 20 years later that we had a breakthrough.”
The eureka moment came from Norway’s National Agricultural University in 2010. A PhD student from Sri Lanka named Aruppillai Suthaparan discovered that the repair mechanism doesn’t activate at night while researching powdery mildew in roses.
“It turned out that the fungus’ defense utilizes blue light from the visible spectrum to facilitate the DNA repair,” Gadoury said. “So a low dose of UV-C light would kill the fungus, if followed by four hours of darkness!”
Supported by grants from the USDA and other institutions, Gadoury became the project director of a multi-institutional and multi-disciplinary team in 2015 to come up with a UV device that decimates the fungus. Besides partners from Norway, other team members include folks from the University of Florida and Rensselaer Institute of Technology, as well as industry partners.
The solution came in the form of a robotic vehicle, centered around a 30-lamp UV-C array that is surrounded by highly efficient reflectors. “It is based on the integrating sphere optical design to create a fog of light instead of a point source. The light is even at any point within the sphere,” Gadoury said.
The first derivation of the robot was pulled by a human-driven tractor. The current version, manufactured by Saga Robotics in Norway, is self-driven by GPS technology. It is tall, straddling the grapevines as it trudges slowly down the rows. Dosages are controlled by varying its speed. It ends its tour four hours before dawn so the fungus couldn’t repair itself.
Chardonnay field trials have been going on for more than a year. John Martini, the owner of Anthony Road Wine Co. and one of the test sites said, “The robot is running over three row of Chardonnay grapes without any spraying. Organic grapes!”
So far, the results are very positive. Besides killing the powdery mildew fungus, the treatments also seemed to have efficacy against downy mildew and small organisms such as mites. Future refinements being investigated include combining a high-resolution imagery system for disease detection and treatment precision.
Gadoury said, “We can create agricultural robots to multi-task. They can detect, assess and treat at the same time.”