Issue link: http://read.dmtmag.com/i/34759
Summer Fruits Peaches on RIDGES S ince coming to Clemson University in 2000, Dr. Guido Schnabel has been taking on the two big disease problems that plague peach growers in the Southeast and many stone fruit growers elsewhere. He’s had some success. Working with other plant pathologists at the University of Georgia, he devel- This planting oped a simple and fast test kit, trademarked Profile, that will tell a peach grower if the brown rot organisms in an orchard are resistant to fungicides—and which fungicides will still work (see “Fast, easy test reveals fungicide resistance”). He and others in his labora- tory are sharing an $850,000 grant to develop these resistance management kits for other diseases in other crops, such as gray mold of strawberry. Now, he believes, he’s onto a method to greatly slow down Armillaria method may stave off Armillaria (oak) root rot. by Richard Lehnert root rot, which growers usually call oak root rot. It can knock years off the productive life of a peach orchard. The new method, which looked good in preliminary tests, is so clever in concept that growers are already trying it in their orchards. The idea is to plant peach trees on ridges, then pull back the soil a cou- ple of years after establishment, exposing the tops of the roots. The trees look strange, as if they’re standing on tiptoes, but Armillariacannot reach the crown to kill the tree. “The fungus does not like to grow above the soil line—that’s the key,” Schnabel said. Commercial scale When Chalmers Carr III, at Titan Farms, saw the initial test results, he planted 200 acres and is the first to try the method on a commercial scale (see “Titan Farms,” page 16). Oak root rot costs peach growers in South Carolina an estimated $4 million a year in direct costs, not counting lost income from sites that can no longer be used because of persistence of the pathogen in the soil. The procedure aims at a weak spot in the Armillaria armor, Schnabel said. The dis- ease, once it affects a peach root, will ultimately kill the root. Moreover, the fungus will move up the root to the crown of the tree. It may kill the tree quickly by shutting off its supply of water and nutrients, or it may move down into other roots, infecting them. The disease infects many kinds of forest trees and produces a type of attractive, edible mushroom called honey fungus, that grows at the base of dead trees. While the fungus does not spread easily by spores, it will grow on living trees and on dead and decaying woody material. It kills its hosts by invading the root collar and girdling the trees, or by causing extensive root death. After a tree dies, a new tree planted near that site is doomed. “Armillaria will last in the roots for years—decades—and even soil fumiga- tion with methyl bromide doesn’t help much,” Schnabel said. “Chemical man- agement has met with limited success because of the protected nature of Armillaria inoculum, being encased underneath the bark of roots and surrounded by soil.” Growers need to replant their peach orchards every 20 years or more often, he said. “The more they use the land, the more infection centers there are.” 22 JULY 2011 GOOD FRUIT GROWER This is what a tree looks like when the soil is pulled away from the collar and the tops of the major roots are exposed. Armillaria does not tend to move above the soil line. www.goodfruit.com GUIDO SCHNABEL