Sep 8, 2015
Project evaluates photoselective netting

It’s affectionately known in some circles of the Washington state research community as the “red, white and blue” project. It has the potential to protect high-value fruit crops from hail, with the added benefit of limiting sunburn in high temperature/light environments.

Washington State University researchers Lee Kalcsits, Sefano Musacchi, Desmond Layne and Tory Schmidt have established a trial investigating the physiology of apple production under photoselective anti-hail nets at McDougal & Sons’ Prospector Orchard in Quincy, Washington.

“This project has three main objectives,” Kalcsits told participants in the International Fruit Tree Association’s 2015 Regional Summer Tour in Washington state. “It’s to understand the impact of netting on the microclimate under the netting versus outside the netting, and to understand how that change in microclimate, change in temperature, change in humidity, change in the wind speed, change in the light environment and how all that translates into the effect on the physiological status of the photosynthetic activity. And lastly, how changes in photosynthetic activity and productivity translate into changes in fruit quality, storability and packout for the grower.”

Preliminary results show that by reducing incoming light by 20 percent, fruit sunburn decreases to levels similar to overhead cooling.

The Washington Tree Fruit Research Commission (WTFRC) and a Washington State Department of Agriculture Specialty Crop Block Grant are funding the project, set to conclude in 2018.

McDougall & Sons, the host orchard, and Wilson Irrigation, which provided shade house structures and an additional research site at the Tree Fruit Research and Extension Center (TFREC) in Wenatchee, Washington, are supporting the effort.

“(TFREC) is where we will duplicate the project on a smaller scale, where we can get physiological measurements you can’t do in a commercial environment,” Kalcsits said.

Kalcsits said efforts are being made to determine the light spectrum of three net colors and how color differences influence the light quality and quantity of incoming radiation throughout the day. The work also seeks to quantify the impact of nets on orchard microclimate, photosynthesis, vegetative growth and tree stress.
“We also want to evaluate fruit and leaf nutritional balance and fruit quality under different light conditions,” he said.

The approach is similar to that taken in many countries (Australia, Italy, Israel and South Africa) where photoselective nets (black, red, blue, green, yellow and pearl) are commonly used to protect high-value fruit crops from hail but have the added benefit of limiting sunburn in high temperature/light environments.

“Washington apple growers who use overhead cooling to limit sunburn face several challenges: increased infrastructure and operational cost, disease spread (including sphaeropsis rot), water logging problems in soil and possible reduced efficacy of foliar treatments,” Kalcsits said.

He said as USDA begins to implement the Food Safety Modernization Act (FSMA), agricultural water sources could require regular testing, may require treatment and potentially could be eliminated from use for overhead cooling altogether.

“Photoselective anti-hail nets represent an alternative to overhead cooling to prevent sunburn and improve packout in apple orchards,” he said. “Netting is being increasingly utilized in Washington state, but relatively little is known about its impact on overall tree physiology, particularly using photoselective colored nets.”

Kalcsits said the project addresses WTFRC research priorities that are of the highest importance: food safety (overhead cooling issues and pre- and postharvest fruit quality) and environmental stress and water relations.

“The high light conditions of Washington state will limit the impact of shading on photosynthetic performance,” he said. “Summer light conditions in Washington state normally exceed light saturation limits for leaves of apple trees. Therefore, reducing light intensity by 20 percent should have a limited impact on maximum light absorption for photosynthesis.

“The altered heat/light load in the net-covered orchard reduces tree stress and should benefit both fruit yield and quality,” he said. “Each net color has a distinct light spectrum signature that may affect responses to environmental cues that regulate vegetative growth, flower and fruit development. Some net colors result in improved fruit skin coloration and shoot vigor reduction.

“The supplier of the netting mentioned that the red color should help with coloring of the fruit,” Kalcsits said. “That’s something we’re going to look at and test. There is an endication we’re going to get that helps with (fruit) color. (Red) increases the warmness, but doesn’t seem to help the sunburn as much as the blue netting that seems to be cooler.”

The 12-acre netting trial was installed at a commercial Honeycrisp orchard near Quincy that was planted in 2013.

Three different net colors (pearl, blue and red) are being tested and compared with an uncovered, overhead cooled control. A second, smaller-scale netting experiment with the same treatments is being established in hoop houses at WSU’s TFREC using 2-year-old Honeycrisp trees, which will first bear fruit in 2016.

“Quantitative assessment of the impact of photoselective anti-hail nets on orchard microclimate and physiology will enable the determination of both the benefits and management considerations of their use in Washington state,” Kalcsits said.

The thrust of the research will determine how the 20 percent reduction in lighting created by the netting impacts wavelengths of light, areas of distribution of light and how the spectrum of light changes to different colors, all impacting how the trees could respond.

Data loggers are located throughout the orchard and anemometers measure wind, all of which is remotely downloaded to the researchers’ Wenatchee location.

“We’re collecting a lot of data,” he said. “It’s really handy that way and gives us a good idea of the changes that are happening. We can measure the increases of humidity in the canopy of trees and the differences in soil temperature.”

Kalcsits said under the trial’s control block, 20-30 percent of the fruit is impacted by sunburn. Measures will be taken next year to install overhead cooling and pursue other traditional measures to reduce cooling.

“In a true control, we will be able to evaluate whether we can replace overhead cooling with netting and not have the (cost) associated with that. We will also see how the netting influences the quality of fruit through packout and storage by looking at productivity measurements.”

— By Gary Pullano, associate editor

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