Using Ultraviolet Light as a Way to Control Powdery Mildew

October 27, 2020

Somchai Rice 

It’s been a weird year.  I spent some time in the field of virology, specifically in the detection of viral diseases in production animal medicine, using polymerase chain reaction (PCR) before I started graduate school.  When I finished my work, I always cleaned my workspace in the hood with an RNase cleaner followed by ultraviolet (UV) light.  When I read an article about how researchers are using UV light to control powdery mildew in the vineyard, a light bulb went off. 

Controlling powdery mildew accounts for the bulk of fungicide applications in the vineyard, especially in Iowa, where the humidity is high.  A team of researchers led by David Gadoury, a plant pathologist at Cornell AgriTech in Geneva, New York, is looking into the control of powdery mildew using UV light.  The idea of using UV light to kill the pathogen responsible for powdery mildew is a new application of already established research.  The research team achieves this by mounting UV lights on tractors or self-driving robots and sending them into the vineyard at night. 

Why at night?  The mildew has a natural defense mechanism that protects from DNA damage caused by UV light.  The mechanism activates when stimulated by the blue light component of the visible spectrum in sunlight.  This blue light component is absent at night, so the mildew’s natural defense mechanism is not activated.  The application of UV light at night can effectively zap the mildew’s DNA and kill it.   

The team found the method to be most effective when four hours of darkness follows the application of UV light.  They have shown suppression of powdery mildew with one treatment per week on Chardonnay and Pinot Noir grapes with three years of research.  Another plus of this new method is the unrestricted timing of the application.  The use of UV light does not depend on weather (rain) like pesticidal sprays.  These automated robots go into commercial production later this year, available from SAGA Robotics in Norway. 

The link to the original article in Wine Spectator can be found here, and a video from Cornell AgriTech can be viewed here

Ulraviolet light on grapes

“An experimental “light sprayer” shines shortwave ultraviolet light on the canopy of a Cornell University vineyard to kill powdery mildew. At night, the fungal pathogen’s natural defensive mechanism against UV light is off, so a small burst of light is all it takes to disrupt the pathogen’s DNA, said Cornell University pathologist David Gadoury.” This picture and caption originally appeared in Good Fruit Grower on August 13, 2019, by Kate Prengaman.  (Courtesy David Gadoury/Cornell University)