Planting Wheat May Help Apple
Growers Manage Disease
By Kathryn Barry
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
Scientific contact: Mark Mazzola, ARS Tree Fruit Research Laboratory,
Wenatchee, Wash., phone (509) 664-2280, fax (509) 664-2287,