Tifton, Georgia: A Peanut Pest Showdown
Lesser cornstalk borer larvae extensively damaged the leaves of this
unprotected peanut plant.
Visit a few of the experimental field sites in Tifton, Georgia, and you're
likely to seeno surpriserows of peanuts, among the state's
top-grossing crops. A closer look might reveal slender insects called thrips
probing around for sap. It's likely many are carrying the tomato spotted wilt
virus (TSWV) that cost Georgia's peanut farmers $40 million in losses in 1997.
Now, check out a different field plot and you might spy another costly
menace: lesser cornstalk borers. Besides chewing on the pods that house the
plant's tender peanut seeds, these caterpillar pests can also contaminate the
crop with Aspergillus fungi that produce aflatoxin, a danger to
Such attacks are unwelcome in commercial fields but are hailed in Tifton's
experimental plots, for they help scientists there hone new pest-proofing
strategies for farmers' peanut crops. Much of this is cooperative research
between scientists of the University of Georgia and USDA's
Agricultural Research Service. Earlier
this summer, for example, ARS entomologist Robert E. Lynch and UGA professor
Peggy Ozias-Akins began field-testing genetically engineered peanuts that repel
borers with an internal insecticidal protein from Bacillus
thuringiensis (Bt) bacteria.
It's not a new tactic, but one few have tried on a legume like peanuts, says
Lynch, who heads ARS' Insect Biology and Population Management Research
Laboratory in Tifton. Ozias-Akins is with UGA's College of Agricultural and
Lacking resistant cultivars, farmers ordinarily apply a soil insecticide to
keep borers in check and prevent them from contaminating the crop with
aflatoxin. But a few bites of the Bt plants can deter the pests from further
In field tests last summer, for example, 90 percent of the Bt plants' pods
escaped serious damage. The transgenic peanuts equipped with a Bt gene patented
by Mycogen, a commercial collaborator, are still a way off from
commercialization, says Lynch.
Aside from regulatory approval, the peanuts must still prove their mettle in
outdoor trials, where conditions fluctuate and borers are generally more robust
than in the lab.
After only a few bites of peanut leaves with built-in Bt protection, this
lesser cornstalk borer larva crawled off the leaf and died.
Ozias-Akins is also monitoring a field plot of peanuts engineered for TSWV
resistance. The product of a gene-gun engineering procedure, the plants' cells
make a virus-derived molecule that interferes with the pathogen's ability to
replicate. In the lab, this protects the plant by robbing the virus of a chance
to cause disease; out in the field, the results are mixed.
"Last year, we had some plants that were clearly infected, and others
that were not," Ozias-Akins reports. If the concept works, however,
commercial peanuts bred from the high-tech strains could offset the virus'
ability to overcome the few resistant cultivars identified thus far.
One, Georgia Green, is now grown on over 75 percent of Georgia's peanut
acreage, reports Albert K. Culbreath, of UGA's Department of Pathology. A
member of the spotted wilt eradication action team, Culbreath helped build an
Internet site farmers now use to assess the risk of an outbreak in their crop.
It's based on seeding times, row patterns, tillage systems, cultivar choice,
and other criteria.
Even with resistant cultivars, Culbreath emphasizes taking an integrated
approach to managing spotted wilt.By Jan Suszkiw, Agricultural Research
Service Information Staff.
This research is part of Crop Protection and Quarantine, an ARS National
Program (#304) described on the World Wide Web at
Robert E. Lynch is
in the USDA-ARS Insect Biology
and Population Management Research Laboratory, P.O. Box 748, Tifton, GA
31793-0748; phone (912) 387-2375, fax (912) 387-2321.
To visit the home page for spotted wilt, go to
"Tifton, Georgia: A Peanut Pest Showdown" was published in
1999 issue of Agricultural Research magazine.