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Planting Wheat May Help Apple Growers Manage Disease

By Kathryn Barry Stelljes
September 6, 2000

Growing wheat before planting a new apple orchard on former orchard land may help growers prevent a crippling condition known as replant disease. Another benefit: It could serve as an alternative to methyl bromide and other soil fumigants typically used to sterilize old orchards before planting new ones.

When nothing is done between taking out an old orchard and putting in a new one, the young trees are often stunted and have small, decayed root systems.

Plant pathologist Mark Mazzola at ARS’ Tree Fruit Research Laboratory in Wenatchee, Wash., discovered that in the Pacific Northwest, replant disease seems to be caused by buildup of four types of soilborne fungi.

While soil where apple trees grow supports these fungi, wheat plants seem to modify the soil to favor other microorganisms. Mazzola found a bacterium in some wheat soils, Pseudomonas putida, that can protect young apple roots from the destructive fungi. ARS has patented use of a strain of this bacterium to prevent replant disease.

The next step is to determine how long wheat would have to be grown as a rotation crop to change the soil microbial community enough to stave off replant disease. Mazzola will also look at whether growing the wheat as a cover crop in existing orchards can reduce fungal populations sufficiently to allow new trees to grow well.

ARS is the chief scientific agency of the U.S. Department of Agriculture. The apple replant disease research is part of a nationwide program of horticultural research within ARS. For more information on ARS research programs that affect horticulture, see the list of "Crop Production, Product Value and Safety" national programs at:

An article about the replant research appears in the September issue of Agricultural Research magazine.

Scientific contact: Mark Mazzola, ARS Tree Fruit Research Laboratory, Wenatchee, Wash., phone (509) 664-2280, fax (509) 664-2287,