CHELAN, Wash. – Fumigating an old orchard then replanting it with new rootstock improves young tree growth and dramatically increases fruit yields – and the bottom line. But it has taken decades of education and advocacy by Tim Smith, WSU Extension educator, for the practice to become the rule rather than the exception.
“Industry leaders credit Tim with helping growers understand the necessity, benefits and techniques of how to fumigate new orchard plantings,” said Ray Faini, director of WSU Chelan County Extension. “The rapid and vast replanting that has occurred over the past 20 years, bringing new varieties to market, could not have happened without this work.”
Planting new root stock on land long used to produce tree fruit has always had negative consequences. In some cases, replant disease can cause up to 100 percent crop failure, but losses average about 20 percent.
“Orchard replant disease has most likely been the most serious disease in Washington state tree fruits over the past several decades,” Smith said. “Total loss of apple production value due to the effects of this disease over the last 20 years exceeds $1.45 billion.”
Smith started his program in the 1980s by setting up several fumigation and post-plant treatment demonstrations trials.
“These demonstrations take five to seven years to complete, so no one in the U.S. had ever documented the benefit of fumigation beyond improved growth in young trees,” Smith said. He was the first to demonstrate a significant increase in yield among properly treated trees.
Over the years, he has shared that information in grower meetings, lectures, grower magazine articles, plot tours, websites and international and national meeting presentations.
As a result, an increasing percentage of replanted orchards are being fumigated. Of the approximately 110,000 acres of Washington orchards replanted over the past 20 years, 42,500 have been fumigated, Smith said.
He also noted that the best way to control almost any plant disease is to build in resistance through breeding.
“Some of the biggest breakthroughs are in new rootstocks. Some are much more tolerant to the soil conditions that lead to replant disease,” he said.
Overall, he said, the increased use of fumigation protocol and new varieties of root stock “really hold out a great deal of hope that someday we may be able to fumigate, plant new root stock and have respectable growth on an old piece of land.”
