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Managing sunburn, heat stress critical for good walnut developmentManaging sunburn, heat stress critical for good walnut development

“Surround is not a silver-bullet approach, but it’s part of our overall program.”


July 18, 2018

4 Min Read
Don Norene, left, and his son, Davin, utilize a systems management approach that includes two applications of Surround each season to protect walnut trees from heat stress.

California walnut farmer Don Norene developed and refined a management program in his Sacramento Valley orchards that has resulted in improved nut quality and higher grower returns.

His systems approach, using various practices including soil moisture monitoring, fertilizers, and separate applications of ethephon, a foliar growth regulator, and Surround, a crop protectant, combine to aid crop yields and plant health.

One of the tools Norene says his processor agrees is effective in producing lighter-colored meats is Surround, a kaolin-based crop protectant by NovaSource. When applied by air, it can protect trees and nuts from sunburn. He says the product generally reduces tree stress from the summer sun, and has shown to be helpful in protecting young trees from intense summer heat.

Norene has seen Howard variety walnuts boil and fry in their green hulls during the summer. “I can go out a couple days later, and what were once good walnuts are a mass of black that will fall to the ground.”

Prior to 2008, he used Surround sparingly. Summer fires that year across northern California had an unintended and unforeseen effect: walnut yields were higher because of the reduced light and heat stress on the trees. “We were smoked out for more than 20 days,” Norene says of the fires. “There was all this diffused light that led to a tremendous walnut crop with tremendous yields.

“We took what we were learning about Surround at the time, and put that with what we discovered from the smoky, diffused sunlight that year, and we discovered there must be much more to this.” He also discovered that the reflective quality of the white film on the trees can reduce plant and nut temperatures by a few degrees. 


Norene believes location also helps. He farms near Wheatland, along the Bear River just upstream from the Feather River. Nighttime temperatures can cool better here than other regions of the Sacramento Valley. This can be helpful to trees and maturing nuts, as the warmer nights don’t allow the internal temperature of the nuts to cool. “We think Surround is more effective for us because of this,” he says.

He farms walnuts and rice with his son, Davin, and they also have rangeland along Cottonwood Creek in nearby Shasta and Tehama counties.

Their Chandler, Hartley, Howard, Vina, Chico, and Ashley walnut varieties are in stratified soil that washed down Bear River from 19th century hydraulic mines. Norene Farms is far enough away from the Feather River to not be impacted by high water tables and seepage during high-water events, like in early 2017’s record rains in northern California. “Generally, our soil is pretty good to excellent,” says Don, who chairs the Walnut Bargaining Association.

Surround is typically applied twice each year to the trees, Davin says — not by calendar date, but based on weather forecasts that call for heat spikes. He also looks at optimal nut size to determine the best date to apply the product. This can tend to fall in the first or second week of June for the first application, with a second application about a week later.


Don says his air service will fly on the product from different directions each time. For instance, if it is applied north-to-south on the first application, he’ll then have it flown on in an east-to-west direction for the second application to gain optimal tree coverage. He prefers it to be applied by helicopter, rather than fixed-wing, to achieve better coverage. “We get all sides of the trees that way,” he says. Applications are made at 30-pound rates with 30 gallons of water per acre.

Davin likes to spray smaller trees by ground. Next year, he intends to apply Surround to fourth-leaf walnuts, using 50 pounds of material and 167 gallons of water per acre. It’s important, he says, to get good coverage and use a product that helps it stick well to the trees. The weather forecast plays a role in spray timing, since rain can wash it from the trees.

Don says yields in his 55-year-old trees can top three tons per acre, with some younger trees producing over four tons. “Our sweet spot plantings of 15- to 25-year-old trees all do over four tons,” Davin says.

It’s not just the direct yield and tree health benefits that can be attributed to Surround, Davin notes. Navel orangeworm (NOW), once thought to be only a pest of concern in pistachios and almonds, is now being discovered as dangerous to walnuts. Surround can help here too, he says.

“You will see a burn spot on the sunny side of the walnuts, and when you crack those nuts open you’ll find a Navel orangeworm in them every time.”

Cultural practices including winter sanitation, have become more necessary in walnuts to help control NOW, Don says. Walnut blight control, properly-timed fertilizer applications, and maintaining good soil moisture also combine to promote good tree health.

“Surround is not a silver-bullet approach,” he says, “but it’s part of our overall program.”

About the Author(s)


Associate Editor, Western Farm Press

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