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 roots—with female nematodes often protruding from root tissue. The worms were identified as root-knot nematodes, Meloidogyne partityla.
"Finding this particular species of nematode is significant because it's the first report of its presence in New Mexico—and 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 Staff.
This research is part of Plant Diseases, an ARS National Program (#303) described on the World Wide Web at http://nps.ars.usda.gov.
Pecan Fun Facts
"New Nematode Plagues Pecan Trees" was published in the March 2002 issue of Agricultural Research magazine.