Strawberry
UVC rays may be better at suppressing powdery mildew in strawberries than fungicide based on results out of Florida and other regions. David Gadoury, plant pathologist with Cornell University in New York says there is no damage to the plant or reduction in yields as a result of the UVC application. He’s the project manager and spokesperson for the study, which has involved a wide range of facilities, a large number of people and about 20 varieties of strawberries.
“We’re at the earliest stages of seeing UV used in disease suppression situations,” he clarifies, adding, “Can we at least tip the balance in our favour? The answer is yes. We’ve measured just about every physiological and metabolic response. Nothing changed [in the plants or fruit].”
So, while the application of UVC rays is still in introductory stages, the results are promising. Powdery mildew is a surface-dwelling pathogen that needs the host to live in order to survive. Therefore, UV rays are a great solution as they can’t penetrate beyond the surface of the plant.
“We have found exposing the plants to treatment at night is even better than fungicide,” he says. “Daytime, the large dose is likely to damage the plant. The timing of the treatments has to be timed to the plant’s biology and ecology. The plant is not stressed and is not responding in a way that impacts quality that we have measured yet.”
UVC rays have proven to be more efficient and effective than UVB rays due to the output levels of the LED lights. The most effective wavelengths are from 250 to 280 nanometers with an effective dose at about 100 Joules per meter square.
Through Wish Farms, a community of strawberry growers in Florida, testing was based on 20 UVC lamps backed by polished reflectors using a uniform dose of 85 Joules per meter square starting one hour after sunset.
“Units of this type have been used in Florida successfully since 2017,” he says.
He’s referring to the device built by the crew at Wish Farms as a unit. It was even named, The Dragon. Trials done on low-trellised hops, grapes and apples were also successful.
“There are some crops that are more sensitive like tomatoes, so do half the dose, applied twice over a couple of days. [In strawberries the application] provided suppression across foliage and fruit throughout the duration of the trial,” says Gadoury.
This was done in strawberries using a fully autonomous robot that moves through the field at nightfall.
There are parameters that need to be observed by growers in terms of speed and proximity to plants for efficacy. These are outlined fully in the study. The low-pressure discharge UVC lamps are the most practical technology when the conveyance device moves at about 4.5 kph. The lamp array density and reflector design are both critical to ensuring uniform dosing through fields.
Since the autonomous robot is simply a conveyance to move the lights throughout the berry field, there are a number of options to consider for movement.
“You can build your own or consider one of the autonomous robots,” he says. “For smaller operations, I’d suggest you’re best off building one of these yourself.”
He estimates the costs to be about $7,000 to $10,000 to have one built or $2,500 to $3,000 if skilled, capable labour is on-farm.
Benefits include the fact that there is no residue on the plants from the UVC treatment, but there are still safety protocols required.
“In particular, you need eye protection and you need to cover exposed skin,” he says. “We also want to make sure your lamps are coupled into a ground-fault circuit to cut down on shock risks.”