Fatal Cherry Disease Is Treed
ARS scientists working with University of California
researchers and industry groups have developed several steps that growers can
take to keep their cherry orchards in peak condition.
Buckskin disease of sweet cherry trees can't be stoppedthat's the bad
news. But researchers have developed methods to keep it in check and growers in
The disease is so named because cherries are small and turn buckskin color,
rather than reddish purple.
Before control methods were developed, tree deaths were averaging between 3
and 5 percent a year throughout the industry. But some growers experienced
catastrophic lossestheir whole orchards died within 2 or 3
yearswhile other growers were unaffected.
Buckskin disease was first noted in California in 1931 and was then quickly
identified in eastern U.S. orchards, as well as in Washington State. After only
20 years, it had wiped out the cherry industry in two northern California
counties, Napa and Sonoma. It remains a potential threat to other counties
"Buckskin disease, also called X-disease, is caused by a
mycoplasma-like microorganism that is carried from infected trees to new
victims by leafhoppers," says Jerry K. Uyemoto, an Agricultural Research
Service plant pathologist.
Uyemoto, who is in the ARS Crops Pathology and Genetics Research Unit at
Davis, California, is a member of a team that has developed several steps that
growers can take to keep their orchards in peak production.
Here's what they recommend:
- Monitor insect populations closely with yellow sticky-board traps. Spray
only when necessary. For example, in orchards known to be diseased, spray when
traps capture one mountain leafhopper, Colladonus montanus, per trap per
week; or spray at the first capture of any Flor's leaf-hoppers, Fieberiella
- Promptly cut down infected trees and completely remove tree stumps. But
first spray with approved insecticides to kill leafhoppers, so they don't just
jump from trees being cut down to nearby healthy ones.
- Monitor ornamental plants such as boxwood and myrtle that are hosts to the
These controls work. Researchers studied orchards in El Dorado county, east
of Sacramento. One grower there, who followed recommendations, confined the
disease to an average infestation rate of 3 percent in his orchard during a
6-year period. Another, who ignored the problem, saw more than 60 percent of
his orchard infected.
The recommendations are cost-effective, too, according to San Joaquin County
farm adviser Joseph A. Grant, who is located in Stockton, California.
He calculates direct loss to his county's growers would run more than $2
million each year. But with insect control and tree removal on about 80 percent
of the county's 7,100 acres of cherry trees, that loss is reduced by
two-thirds, for an annual benefit of almost $ 1.4 millioneven with insect
control costs running about $70 per acre.
"If growers want to fill in where dead trees were removed or establish
new orchards, they should plant trees that have mahaleb rootstock, which is
immune to the buckskin pathogen," says Uyemoto.
These trees should have multiple scion buds grafted high up on the
rootstock. Later, if individual branches that develop from the buds become
diseased, growers can cut them off without harming the rest of the tree.
In collaboration with colleague Bruce Kirkpatrick at the University of
California-Davis, the latest research focuses on developing more sensitive
tests to better identify the disease-causing organism. A test called
PCRpolymerase chain reactionis more accurate and may put the finger
on additional plants that serve as reservoirs for the organism.
ARS worked in close cooperation with the University of California-Davis and
two industry groups, the Cherry Growers' Industry Foundation and the California
Cherry Advisory Board. By Dennis Senft, ARS.
Uyemoto is in the USDA-ARS
Pathology and Genetics Research Unit, University of California, 380
Hutchinson Hall, Davis, CA 95616; phone (530) 752-0309, fax (530) 754-7195.
"Fatal Cherry Disease Is Treed" was published
in the September
1995 issue of Agricultural Research magazine.