WENATCHEE, Wash. — Wind machines, heaters and irrigation water are the main tools tree fruit growers use to fight spring frosts, but Washington State University scientists say a fourth tool may be the best yet.
Cellulose nanocrystals — known as CNC — from wood or plant fiber has “excellent thermal properties sort of like putting on a jacket,” Matthew Whiting, WSU plant physiologist, told growers at the Jan. 15 WSU Northcentral Washington Stone Fruit Day in Wenatchee.
Whiting and three colleagues are in the second of three years of field trials spraying CNC solution on fruit trees to protect buds from frost damage. Xiao Zhang, associate professor at WSU Tri-Cities’ Bioproducts, Sciences and Engineering Laboratory, knew about CNC from working in a private industry forest products laboratory. He and Whiting tried it as a tree fruit bud frost protectant in spring of 2017.
The results were positive enough that they applied for and received a $500,000 study grant from USDA and a $100,000 grant from the Washington Tree Fruit Research Commission.
Beside Zhang and Whiting, Qin Zhang, director of WSU’s Center for Precision and Automated Agricultural Systems, and Changki Mo, associate professor of mechanical engineering, are working on the project.
Wood fiber waste from pulp mills is converted into cellulose crystals. Nano is a microscopic measurement. A solution of CNC is sprayed on trees. Good wrap around coverage is important and electrostatic sprayers are best for that, Whiting said. Testing will be done with orchard airblast sprayers, he said.
When the solution dries it can improve cold tolerance by 6 degrees, he said, agreeing that a lot of times a few degrees makes a big difference in frost protection. A trial in cherries also showed 40 percent higher yield in fruit, he said.
The transparent coating is thin enough that it doesn’t appear to impede bud development.
Duration is a key question.
“We know it will last a few days. We’re more interested in if it will last a few weeks. It depends on weather and how easily it is washed off,” Whiting said.
Applications have been 2 percent CNC to water but “WSU is trying to protect its intellectual property on formulation so I can’t give you all the rates,” he said.
Field trials will be expanded this spring in Yakima and Wenatchee orchards.
Growers are looking for better tools, as frost protection is a perennial challenge, he said.
Heaters are expensive and inefficient. Growers use them to keep temperatures up around trees but the heat dissipates. Wind machines only work during inversions when there’s warm air to pull down from above. Irrigation water, which freezes on buds and holds them from going below freezing, depends on its availability and leaves wet, cold soils.
“All evidence is CNC will be more effective,” Whiting said. “It’s promising but preliminary. We need a few more years of larger trials to have more confidence it’s a viable solution.”
It’s being tested on wine grapes and should be effective on citrus, vegetables — just about any crop needing frost protection, he said.
“A real benefit,” he said, “is it is a green, renewable and sustainable solution.”