May 8, 2023
Wood pulp on tree fruit buds guards against frost damage

Tree fruit and vineyard growers are among those subjected annually to threats of significant economic losses from cold damage to reproductive fruit buds. An emerging approach is providing frost control, and researchers are optimistic regarding its potential.

Electrostatic application of cellulose nanocrystals (CNC) dispersion to fruit buds through spray agents forms an insulation layer. Across multiple tree and vineyard crops, trials are showing CNC-treated buds are more resistant to freezing than untreated buds. Cold hardiness was improved by 2˚-4˚ Celsius (3.6° -7.2° Fahrenheit) with CNC treatment.

“(Early) results demonstrate great potential for field applications of CNC to improve specialty crop yield security by protecting reproductive buds from cold damage,” said Matthew Whiting, scientist, professor and Extension specialist in Washington State University’s (WSU) Department of Horticulture.

Bill Shane continues a study of frost control treatment on Michigan peach trees and other fruit crops. Photo: Gary Pullano

“Losses from cold damage plague growers worldwide,” said Whiting, a lead researcher in the project that has received funding from USDA’s National Institute of Food and Agriculture. “Our technology is not crop-specific, at least not among the crops we have looked at so far. The protective effects should apply to any crop under threat of cold damage.”

This year, research includes large-scale trials with growers to look at different crops, sprayer technologies and formulations.

The research came about after a conversation with Xiao Zhang, chemical engineering and bioengineering professor at WSU, who was studying cellulose nanocrystals, which have excellent thermal properties and create a barrier when they’re sprayed and subsequently dried.

“I told him it would be interesting to try this on fruit crops to control frost damage,” Whiting said. “It does create an insulating layer.”

Michigan peaches targeted

At the Michigan Spring Peach Meeting in March, Bill Shane, senior Extension tree fruit specialist at Michigan State University, reported on his study of CNC treatment on peach trees and other fruit crops.

“In Michigan, freeze is a major problem for our industry,” said Shane, who referred to a chart of average peach yields since 2007 that shows the periodic production dips related to freezes. “It makes it difficult for Michigan to do a market for peaches, and keep customers because of these fluctuations. Anything that we can do to help prevent the amount of damage that freezes are creating is a great thing.”

In lower southwest Michigan, growers enlist wind machines and other methods to help with frost control.

“We have inversions, so people use micro-sprinklers under the trees, copper solutions and other techniques,” Shane said. “They help, but we’re always looking for something that’s new.”

Patented technology

Shane outlined the basics of the technology patented by WSU that provides nano- and/or micron-sized particles which, when applied to plant parts such as buds, form a non-hydrophilic deposit (makes the buds less likely to have water in them) or film with low thermal conductivity, protecting against damage from ice nucleation and cold stress.

“It looks like a paste,” he said. “A concentrated form is actually diluted to 2.5 to get a milky, thin yogurt-type texture. It’s something that is sprayable.”

Shane said the material has some anti-freezing qualities, so it can be sprayed in below-freezing conditions.

“It looks much like you’re using Surround. It’s a very safe material, a non-toxic material based on wood pulp,” Shane said. “It does coat pretty well if you get it on the surface. It takes some rubbing to get it off.”

Beginning in 2022, Shane’s crew conducted CNC trials on grapes, peaches and apricots.

“We hoped from a research standpoint we would have some freezing in order to sample,” Shane said.

Because Mother Nature was not cooperative, buds were collected and subjected to controlled temperatures in the lab to see if the spray provided protection compared to plants and buds that were not protected.

Researchers subjected buds to different temperatures and then dissected them to check for internal damage. Tests on peach fruit buds took place in April 2022. In the untreated control group, the bud survival rate was lower.

“We saw about the same effect with grape buds in that year. It’s about a 10% difference in the amount of bud survival with the application,” he said.

“It’s less than what was reported in Washington state in their trials,” Shane said, noting the trial will be repeated this year.

Wood a determinant

Shane said WSU researchers have determined that using different types of wood to make the cryoprotectant results in different effects. Whiting confirmed that the type of wood does influence how strong the protection is. He said there may be a few reasons why Shane didn’t obtain the same results.

A key finding is that electrostatic application systems are best because of the spray coverage, Whiting said.

“We are now engaged with the licensee in research to optimize the material for efficacy and cost,” Whiting said.

Whiting said the technology’s intellectual property is licensed by Sappi Limited, and it is working toward registration and commercialization.

“We’ve been doing trials with growers for several years now, mostly in tree fruit crops,” Whiting said. “Large-scale trials with many growers are ready to go. We did a pilot plant processing this winter to produce enough to cover hundreds of acres. We have distributed material to collaborating growers who will treat the blocks if needed, which, so far (this spring), it hasn’t been.”

— Gary Pullano, senior FGN correspondent

Top photo: An electrostatic sprayer disperses cellulose
nanocrystals in a Washington orchard. Photo: Matt Whiting

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