Issue link: http://read.dmtmag.com/i/34759
In this test, Guido Schnabel is comparing the performance of peaches planted on ridges with those planted in the conventional way. His initial work was done with peaches in pots. This bed-forming tool was used to make ridges on which to plant trees that will start their life growing above deeply buried, old roots infected with Armillaria. Peach growers use tillage to bring up the old tree roots and root rakes to sweep up all the roots they can. But peach roots are deep, three feet and more. When a new tree’s roots touch a dead, infected root, “the fungus jumps from the old root to the new root as soon as the new root approaches the dead root,” Schnabel said. “The fungus moves up the sec- ondary root to the primary root, then into the crown of the tree. The fungus will grow around the crown of the tree and shut off its water supply. That’s when the tree dies.” In one of his test plantings on a replant site, four-year-old trees were already dying. “Planting on a mound will keep the roots “The fungus may kill a root, but it can’t infect the collar and kill the canopy.” —Guido Schnabel shallow for a year or two, but as they roots go deeper, they contact old, infected roots and become infected themselves,” he said. Ridge But that bit of knowledge, combined with the knowledge that Armillaria does not like to grow above the soil line, spawned an idea. How about planting on a ridge and then blast- ing the soil away at the tree base? Schnabel thinks growers can do that using an air blaster. “The fungus may kill a root,” Schnabel said, “but it can’t infect the collar and kill the canopy. Other, uninfected roots will take over more responsibility with new flushes of roots. Eventually, the tree will die if too many roots are infected. But you can buy yourself four or five years. Growers say they need eight to ten years for an orchard to make money.” Schnabel started his tests with trees in Impressed by early research results, Titan Farms planted 200 acres of peaches on ridges to try out this new approach to Armillaria root rot. open-bottom, fabric pots put into the ground in infected sites known to have heavy disease pressure. “After five years, nearly all the trees planted according to grower standard were dead,” he said. “But only 10 percent of the trees planted in pots initially and later with their roots exposed died. We think we can significantly extend the life of orchards on Armillaria root rot-infested replant sites.” On the road to this discovery, Schnabel tried other things. He found, for example, that injecting infected trees with the fungicide Alamo (propiconazole) would kill the fungus and halt the expansion of the fungus from the infection center. This product and the injection method are used by professional arborists to protect valuable landscape trees. “This may work for someone with a small orchard,” he said, “but it’s too labor intensive for most growers. A smaller grower can protect the peach site by injecting infected trees and actu- ally stop the root-to-root spread. Infection centers could be kept small and isolated.” Schnabel also tested a biological control agent, Tricho- Honey fungus mushrooms grow at the base of dead and dying trees. The mushrooms are rated edible and choice by mycology buffs. www.goodfruit.com derma, which has some uses in controlling pathogenic fungi in soil. After five years of testing on two grower sites, he found it had no effect on Armillaria. Other researchers have also found this method needs careful refinement to match the strain to the specific disease. Schnabel believes Armillaria is too well protected inside dead roots for either Trichoderma, fumigation, or soil drenches to be effective. Armillariais a problem in cherry orchards in Michigan and on grapes in California. • GOOD FRUIT GROWER JULY 2011 23 RICHARD LEHNERT GUIDO SCHNABEL GUIDO SCHNABEL RICHARD LEHNERT