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Sweet Cherries Can be Grown with Less Water

PULLMAN, Wash. — Sweet cherries apparently are not as thirsty as most growers have believed, Washington State University researchers have found. That’s good news for growers facing reduced water allotments this spring.

Washington is the nation’s leading producer of sweet cherries. Sweet cherries are typically harvested from early June through early August and shipped fresh to markets all over the world. The crop returned about $169 million to the state’s 2,400 growers in 2003.

Following the state’s 2001 drought, Matthew Whiting, a horticulturist at WSU’s Prosser Irrigated Agriculture Research and Extension Center, and Roberto Nunez-Elisea, a horticulturist with Oregon State University, undertook a three-year experiment to find out if quality sweet cherries could be grown with less water.

The scientists compared the effects of two deficit irrigation treatments with a control treatment. Each week, all of the trees in the control block received 100 percent replacement of the volume of water lost by evaporation from the soil surface and transpiration from the plants.

In the two experimental treatments, just half of the water was replaced, but each in different ways.

Among other things, the scientists measured the trees’ response to the treatments as well as fruit yield and quality. They documented the trees’ vegetative responses, measuring shoot length to see if water deficits inhibited growth. They also measured fruit diameter to compare fruit growth rates.

“Nobody would go to the extreme that we did with 50 percent water reduction,” Whiting said, “but over the course of three years we found there was no consistent negative effect of either deficit irrigation strategy on fruit quality or yield. I could say quite confidently that every cherry grower in the state could use less water and grow the same quality of fruit.”

Concern that water stress might trigger increased flower bud induction and production of poor quality fruit did not pan out.

“We saw no effect on fruit buds per spur or the number of flowers within each bud,” Whiting said.

Tree size made no difference either. Dwarfing rootstock was compared with an intermediary rootstock and an industry standard. “Neither the smaller nor larger trees were more or less susceptible to stress,” he said.

“In our situation we found it was actually difficult to impose a significant physiological stress on a cherry tree between bloom and harvest, though this will vary among orchards and their ability to retain water in the root zone,” he said.

He is trying to calm the fears of growers who call him. “Don’t get too stressed because we know that cherries can handle a certain degree of water stress and be O.K.”

Sweet cherries are grown fairly widely in the state, but most production is concentrated in the Yakima Valley and Wenatchee area. Strong demand and good prices have fueled an increase in production. Bearing acreage in the state has increased from 16,400 acres in 1995 to 26,000 acres in 2003.

While expansion has slowed in the last couple years, Tom Schotzko, WSU extension economist, expects it to continue. “I don’t think they’ve really reached anywhere near the capacity that the domestic market can absorb at decent prices. That’s where the drive has come from causing current growers to go out and plant more trees and new growers to plant trees. It will probably take a couple years of poor prices to cause growers to lose interest in planting more trees.”

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