A Guardian Angel for Peach Trees
Though the top is dead from peach tree short life disease, suckers sprouting at
ground level show the roots remain alive.
Horticulturist Thomas G. Beckman has found a "guardian angel" for
disease-threatened peach trees. Beckman and Clemson University scientists
co-developed a new rootstock, called Guardian, that protects trees from peach
tree short life (PTSL) disease.
The leading cause of tree death in the southeast region, PTSL costs peach
growers about $10 million in damages annually. It is seen as a sudden collapse
and death of peach trees in the spring, usually when the tree is between 3 and
7 years old.
U.S. growers produce about 2.6 billion pounds of peaches annually. Now,
naturally sweet peaches, packed with flavor, have Beckman's new rootstock to
protect them, ensuring their arrival to grocery produce sections and local
"To date, the performance of Guardian rootstock on PTSL sites in the
southeastern United States has been exceptional," says Beckman, a
scientist with the Agricultural Research
Service's Southeastern Fruit and Tree Nut Research Laboratory in Byron,
The first commercial-scale trial of Guardian began in 1989.
Scientistsplanted trees in South Carolina and Georgia to compare those
grown on Lovell and Nemaguard--two commonly used commercial rootstocks--with
trees grown on Guardian. Lovell has tolerance to PTSL, and Nemaguard has
resistance to root knot nematodes. Guardian has a unique combination of both.
Shaving away bark with a pocket knife, horticulturist Tom Beckman examines a
tree killed by PTSL disease. The healthy tree to the left is growing on the new
In the trial, completed in 1996, no Guardian rootstock trees were lost to
PTSL in South Carolina and only 20 percent were lost in Georgia. Beckman says
the trees in South Carolina were grown under best management practices, while
the trees in Georgia were planted under a worst-case scenario--no lime, fall
rather than spring pruning, and no nematicides.
In comparison plantings, PTSL claimed 97 percent of Lovell rootstock trees
in South Carolina and 40 percent in Georgia. For Nemaguard, 95 percent in South
Carolina and 80 percent in Georgia succumbed to the disease.
"While we're not sure what causes short life, we do know some things
that can help," Beckman says.
Keeping soil pH above 6 to reduce acidity, pruning just before bloom in
February or March, and fumigating to control ring nematodes are some of the
most important things growers can do.
Horticulturist Tom Beckman checks greenhouse-grown Guardian hybrids.
"We believe ring nematodes predispose the tree to injury by winter cold
and bacterial canker," says Beckman. "Unfortunately, it is not always
cost effective for growers to fumigate routinely." The Agricultural
Research Service and Clemson have jointly applied for a plant variety
protection certificate on Guardian rootstock. They released Guardian to
nurseries in 1993.
Demand for Guardian seed initially outstripped supply, because a severe
frost in 1996 destroyed the Byron crop and reduced the Clemson crop. The
rootstock is available only through licensed nurseries, and demand has been
from 1 to 2 million seeds per year for the Southeast alone. Beckman says as of
1997, supplies have been adequate to meet commercial needs. He is confident
that establishment of a seed bank as a hedge against future failures will
ensure adequate supplies.
Beckman is gauging Guardian's adaptability in other regions. He and
cooperators are testing it at 20 sites in North America, including Canada. It
will be a few years before he can measure results, but the rootstock's future
as a guardian angel is bright.
"Guardian has excellent potential to replace both popular commercial
rootstocks in the Southeast," says Beckman.--By
Tara Weaver, Agricultural
Research Service Information Staff.
Thomas G. Beckman is at the
USDA-ARS Southeast Fruit
and Tree Nut Research Laboratory, 21 Dunbar Rd., Byron, GA 31008; phone
(912) 956-6436, fax (912) 956-2929.
"A Guardian Angel for Peach Trees" was published in the
October 1998 issue of Agricultural Research magazine. Click here to see this
issue's table of contents.