John Edstrom, who helped boost almond yields and prove walnuts could be grown on Colusa County's west side, will retire on Jan. 1.
For the past 26 years, the UC Cooperative Extension farm adviser has studied almonds, walnuts and prunes, working with growers in Sutter and Yuba counties as well as Colusa. Growers credit Edstrom's research and extension efforts for transforming almond and walnut farming systems.
Colusa County farmers knew walnuts thrived on deep, fertile soils, in which their roots could sink 10 feet to anchor a towering tree. They knew the land near Arbuckle, with its shallow soils and unpredictable clay layering was suitable only for the more surface-rooted almonds that have been growing there since the 1890s.
"Nobody grew walnuts on the west side at all," says Colusa County grower Gary Henderson.
Seeking opportunities for growers to diversify their crops, Edstrom planted a test plot of walnut trees at the Nickels Soil Laboratory in Arbuckle in 1986.
Edstrom and UC Cooperative Extension farm advisor Bill Krueger set up a walnut orchard with 202 trees per acre, much closer spacing than the 60 trees per acre found in a traditional orchard. Edstrom selected two varieties that produce a large proportion of walnuts on lateral buds, which allows for hedgerow planting and mechanical pruning. Each year, a giant hedger with eight 36-inch saws buzzed down one side of the tree rows, cropping back branches and encouraging production. In alternate years, they pruned the opposite side of the trees. Rather than being flood irrigated as most walnut orchards, the Nickels orchard was watered and fertilized using precise drip irrigation.
The dense plantings compensated for the marginal soils.
"Harvesting two tons per acre is considered a good yield," Edstrom said. "In our first planting, we peaked at three and a half tons per acre."
"We've planted 120 acres, copying the varieties and hedgerows at Nickels, and it's been very successful," Henderson says. "The Nickels plots proved this could be walnut ground."
Henderson, who is a trustee of the Nickels Soil Lab, grows almonds, but said it's nice to have another crop.
Nearly 25 years later, Colusa County grows over 5,000 acres of walnuts.
Almonds are the county's top crop, with over 35,000 acres of almond trees.
When regulators banned the use of organophosphates for dormant sprays, Edstrom and his colleagues developed treatments with Bacillus thuringiensis (Bt) as an environmentally friendly alternative for pest control. Recently he was instrumental in identifying and reporting two diseases new to California almonds–powdery mildew and bacterial spot – and in identifying and reporting a new pest, almond rust mite.
The economic impact of all this research has been significant, according to Bob Curtis, research director for the Almond Board of California, which has funded many of Edstrom's research projects.
"For instance, average almond yields in Colusa County, where Nickels is located, have quadrupled over the past 20 years from about 600 kernel pounds per acre to 2,300–2,400 pounds," Curtis says. "Industry wide, over this same period, average yield has doubled from about 1,100 kernel pounds per acre to about 2,200 pounds per acre. To a large extent, yield increases are a result of these improved practices."
The growth in production has contributed to an increase in farm revenue of nearly $100 million for Colusa County over the past 20 years.
"I can't imagine having a more fulfilling career than the one I have enjoyed as farm adviser with UCCE," Edstrom says. In retirement, Edstrom plans to do private consulting for Central Valley almond and walnut growers.