New Nematode Plagues Pecan Trees
For the past few years, in an
orchard in Dona Ana County, New Mexico, yields from mature pecan trees,
Carya illinoinensis, have been in decline despite growers' use of normal
fertilization and irrigation practices. So Agricultural Research Service and New
Mexico State University scientists agreed to work together to get to the root
of the problem.
The low-yielding pecan trees, growing in sandy soil in two widely separated
irrigation terraces, had chlorotic (yellowed) foliage, substantial dieback of
branches in the upper canopy, and nematode-infested roots.
In October 2000, a team of New Mexico State University scientists led by
plant pathologist Stephen Thomas collected fresh pecan roots and sent them to
the ARS Nematology Laboratory in Beltsville, Maryland, for identification of
the nematode species.
Examination by nematologist Zafar A. Handoo revealed the presence of many
small galls and egg masses on feeder rootswith female nematodes often
protruding from root tissue. The worms were identified as root-knot nematodes,
"Finding this particular species of nematode is significant because
it's the first report of its presence in New Mexicoand only the second
report of it in the Western Hemisphere," says Handoo.
Host range tests conducted in Texas, where this nematode was first
discovered in 1996, revealed that it prefers to feed on hickory, pecan, and
walnut trees. There are now reports of the nematode surfacing in Georgia and
Arizona, as well.
Although M. partityla is not likely to kill the pecan trees, it will
debilitate them and lower their productivity to a point where the orchard may
no longer be profitable.
Nematodes are microscopic worms that attack plant roots and cause billions
of dollars of agricultural losses each year in the United States alone.
Root-knot nematodes are particularly important root parasites that can
seriously damage many economic plants and crops worldwide.
New Mexico is the second largest pecan-growing state, behind Georgia and
ahead of Texas, producing 32 million pounds in 2000. This was down 33 percent
from the record 52 million pounds harvested in 1999. There are currently over
30,000 acres of pecans in New Mexico alone.
To help avoid future threats to the state's $50-million pecan industry,
scientists are now evaluating control measures and educating growers to
recognize M. partityla and prevent its spread. Not only are pecans a
valuable cash crop, they are also an important source of trace elements and
other dietary nutrients.By Jennifer
Arnold, formerly with the Agricultural Research Service Information
This research is part of Plant Diseases, an ARS National Program (#303)
described on the World Wide Web at
Pecan Fun Facts
"New Nematode Plagues Pecan Trees" was published in the March 2002 issue of Agricultural Research magazine.