Using UV Light to Kill Powdery Mildew on Grapes
by Steve Elliott
Western IPM Center
Instead of relying solely on fungicides to control powdery mildew on winegrapes, growers may one day – and one day reasonably soon – have an effective non-chemical option: light.
Specifically, light in the form of spore-killing ultraviolet UV-C radiation, delivered directly to the plant by a self-driving tractor moving through vineyard rows autonomously at night.
As futuristic as that sounds, the technology exists and is being field tested this fall thanks to a unique collaboration that includes:
- U.S. Department of Agriculture Agricultural Research Service and Oregon State University researchers, who are validating the effectiveness of UV-C light in killing powdery mildew in Oregon’s climate.
- Willamette Valley Vineyards, which tested early prototypes and invested heavily in the research – and the autonomous tractor.
- Puren Solutions, a local Corvallis company that manufactures UV-C sanitation systems for industrial and agricultural applications.
- Engineering students at George Fox University, who designed a two-row light box that retracts, making it more maneuverable and farmer-friendly.
What’s more remarkable is that most of the partners were looking into UV-C independently before coming together for this project.
On the academic side, Alexander Wong, who was then a PhD student at Oregon State University, and Walt Mahaffee of the U.S. Department of Agriculture’s Agriculture Research Service were looking to see if earlier work done on UV-C light at Cornell University was applicable to the Pacific Northwest, where disease pressure is much higher.
Wong and Mahaffee built a prototype delivery system – an array of UV-C bulbs shielded inside a light box, designed to test single-pass applications of the UV radiation.
“We put it on the tractor’s three-point mount,” Mahaffee said. “That means you’re not pulling a trailer and you can turn easier and it’s a little more functional for a grower to do. We also tried to make the light array a size that got the dosage we thought was needed in a time frame that could be delivered by a tractor in one pass because tractors can only go so slowly.”
They had some success but also determined they needed to deliver more UV-C energy. This meant either increasing the intensity of the UV-C radiation delivered, or moving through the vineyards more slowly, or making multiple passes a night. The latter two options make using UV-C less practical for growers, so the researchers started exploring ways to increase intensity.
At the same time Wong and Mahaffee were doing their studies, David Markel, the research and development manager at Willamette Valley Vineyards, was also looking at whether UV-C could manage disease on their grapes.
“This was right when COVID hit, and Jim Bernau, who founded Willamette Valley Vineyards, was looking for ways to mitigate that risk and found that UV-C light was being used to sanitize airplanes and things like that,” Markel said. “He saw there was a company in Norway using UV light for managing powdery mildew. He was fascinated by this robot in Norway and I convinced the company to sell us a unit.”
During Markel’s research into UV-C he discovered Wong and Mahaffee were already working on the same thing, right in his own backyard. So when the Norwegian unit arrived, they tested it together.
It was not a success.
The unit, which looks a bit like an arcade photo booth, can work on the flat ground of a hoop house but simply was not designed for the uneven terrain of an Oregon vineyard. To make UV-C work in Oregon, they’d have to build something completely new.
First, they connected with the engineering department at George Fox University where a senior design team began working with them to design and build a new array. Next, Puren Solutions contacted them after reading a Western SARE report on their research and joined the partnership to build version 3.0.
This iteration of the array has dual light boxes that can treat two rows at once and the ability to retract the boxes at the end of a row so turning and maneuvering are easier. Puren’s light solution will more than double the UV-C dose while increasing the tractor speed, making the application more practical. The team plans to field test the unit this fall.
Wong, who was funded by Western SARE as graduate student at OSU and now works for the commercial nursery Fall Creek, has also been developing and testing an integrated disease management program that combines UV-C treatments with the fungicides growers currently rely on – and over-rely on.
“We see a lot of fungicide resistance develop quickly in powdery mildew,” Wong said. “Management of plant diseases needs to be integrated. You’re not spraying your way completely out of it, and you’re not going to be able to light your way completely out of it. But the addition of UV-C when you have really high disease pressure means you can rely less on fungicides.”
Specifically, Wong found that using the UV-C early in the season, when powdery mildew is at its worst, growers could extend the time between fungicide treatments and stop using some of them much earlier after bloom.
“We could significantly reduce fungicide use while still maintaining very good disease control,” Mahaffee said. “And Alex’s work also clearly shows very good efficacy of the UV-C treatments under lower disease pressure, so we can probably get by with less frequency or a lower dose, which means you could run it faster through the fields.”
Stay tuned. The field tests and continued refinement of the system promises to be illuminating.