DONALD W. MEYERS – YAKIMAHERALD.COM – NACHES — When a 2-acre stand of Honeycrisp apple trees was covered with shade netting at Long Ranch, foreman Eladio Gonzales estimated it would take about a year to see how well it worked at protecting fruit from sunburn.
But just month later, the difference is as clear as night and day.
“You can see how bushy and happy these trees look,” Gonzales said, pointing to the shaded trees with lush branches bearing large apples. A similar stand without the protective covering appeared less dense, and some of the fruit bore large, brown spots, a sign of too much sunlight.
Thousands of acres of orchards in the Yakima Valley are covered with the polyethylene material as growers strive to ensure as many apples and cherries as possible get top dollar. Nets on Ahtanum Ridge are visible for miles, almost looking like a huge building from a distance.
Netting has been used in the tree fruit industry before, but usually as a way to protect fruit from birds and hail damage.
But there was another element that fruit can need protection from — the sun.
“Yakima Valley has more sunlight intensity than needed to grow the fruit,” said Jim Doornink, a Wapato-area grower and commissioner with the Washington Tree Fruit Research Commission.
While sunlight is needed for photosynthesis, too much sunshine — in particular ultraviolet rays — can cause sunburn, which results in either losing the fruit or lower prices because of diminished quality.
Excessive sunshine can also stress trees, throwing them into “survival mode” where they start sucking nutrients from the fruit in an effort to stay alive, Gonzales said. That relegates most of a tree’s fruit to low-quality status.
Among the ways orchardists have tried to keep tree fruit cool and unburned are overhead irrigation, with water used to keep the fruit from overheating, and applying a sunscreen solution.
But when used to cool trees during a heat wave — much like the one much of the state is going through now — overhead irrigation can cause the trees to get too much water, which also stresses the trees, Gonzales explained. The sunblock is effective, but it leaves a milky-white residue on fruit and trees and can inhibit growth.
But the nets offer a way to reduce the sunshine to a safer level, and a Washington State University researcher has the data to verify it.
Following up on research by Brazilian scientists, WSU assistant professor Lee Kalcsits conducted a 2015 study on whether netting would affect plant growth in Central Washington’s orchards. His study found that the netting reduced the fruit’s surface temperature, and that sunburn was significantly reduced when compared to plants exposed to the full rays of the sun.
The netting still allows light, rain and air through, but it reduced the intensity of the sunlight by as much as 15 percent, and some materials can block the ultraviolet rays in particular.
Gonzales said Long Ranch’s netting reduced the surface temperature of the fruit by 10-12 degrees, even though the ambient temperature under the nets was the same as outside.
Another sign the nets are working is more fruit growing to maturity. In an uncovered section of Long Ranch, apples littered the ground around the trees, while few were found near the trees under the nets.
Some of the area’s larger growers started using the netting, said Jason Craig, a field support and sales representative with Union Gap-based Extenday. Now, based on their success, smaller growers are adopting the technology to improve their fruit yield.
“More and more (growers) are coming online because it’s a tight-knit industry and they all talk to each other,” Craig said.
In addition to the netting, Extenday also makes reflective ground sheets that can bounce sunlight into the lower branches of trees, helping fruit that would be shaded by the higher parts of the tree get adequate light to develop fruit.
Netting is not without its challenges, though.
Doornink said the netting has to be securely anchored, as it can become like a sail in high winds.
It also requires installing a trellis system. At Long Ranch, Gonzales said the stand they were using already had a cherry trellis that made hanging the net easier, but future expansion — he said grower Gary Long is looking to expand the net coverage to 6 acres — will require installing taller poles to properly hang the nets.
It’s also expensive, with prices ranging from $2,500 to $4,500 per acre. But Jason Craig, a field support and sales representative with Union Gap-based net-maker Extenday, said the money is more of an investment that pays dividends at harvest time, when a 40-pound box of premium Honeycrisps can go for $80-$90.
“Anything we can do to improve the quality of the fruit helps,” Craig said.
- Picture: SHAWN GUST – Yakima Herald – Protection Net