Germicidal ultraviolet light (UV-C) applications have been helping to manage diseases in grapes and strawberries. However, trials conducted by Cornell researcher Kerik Cox and his team have determined that UV-C can also be an effective alternative to antibiotics and fungicides in apple crops.
This method exploits the unique properties of pathogens that have evolved alongside light, namely their inability to repair DNA damage caused by UV-C exposure during nighttime operations. The exposure disrupts the ability of organisms to replicate, breaking the DNA helix and making different base pairs bind to themselves. Organisms can’t grow or make protein, which initiates cellular death.
Given that the fungus causing powdery mildew on grapes grows almost entirely on the surface of the grapevine’s green tissue, it can also be a prime target for UV-C-based treatments.
“The trick is that many organisms can repair this damage in blue light. The pathogens that cause fire blight and apple scab have the same repairs, but if you apply it within four hours of darkness, they can’t repair,” Cox explains.
The team built a UV-C device collaboratively with their colleague, David Gadoury. The towable arch on wheels is lined with UV-C bulbs emitting germicidal ultraviolet light. An array of reflectors causes a reflective light cloud to reach the underside of the leaves and the canopy interior.
The 8-ft. tall contraption is powered by an attached generator and pulled by a small tractor. Its design allows it to treat a wide range of plants without harming them. The arch is powered up and pulled very slowly (about 1.75 mph) through the fields.
The UV-C light must contact the fungal pathogens to damage them. Application frequency needs to be between three and seven days.
“We need the organisms to love dry weather and be on the leaf surface, such as in grapes and strawberries, to go after powdery mildew,” Cox says. “They should be exposed and transparent to the environment so that the UV light can penetrate and kill the spores. The key is trying to balance the dose to kill the pathogen but not harm the host.”
Over multiple years and many different crops, the apples have not been harmed. While antibiotics and yeasts have been used to control disease, they can be expensive. The UV-C device isn’t energy-intensive. Additionally, the bulbs are durable and only fail when struck by a stray branch.
The unit costs about $15,000, including the setup, wiring and coding. In comparison, a streptomycin application over 500 acres is approximately $25,000.
Cox says the system should also work well in vegetables and nurseries. So far, they’ve given away the documents for free to any interested growers. He hopes a company will commercialize the process to help further reduce pesticide use.
Contact: FARM SHOW Followup, Kerik Cox, Ph.D., Cornell Agritech, 322 Barton Lab, 15 Castle Creek Drive, Geneva, N.Y. 14456 (ph 315-787-2401; kdc33@cornell.edu).