When
soybean producers search through the tremendous number
of varieties for the ones that will suit their fields,
they need to keep disease resistance high on their list
of criteria, says Terry Kirkpatrick, a University of
Arkansas Division of Agriculture plant pathologist.
"One characteristic by itself doesn't make a variety
successful, but one bad characteristic for a variety
planted in the wrong place can ruin a crop," Kirkpatrick
says.
"I think that some producers may be choosing a variety
because one certain characteristic, for example Roundup
resistance for weed control, stands out in their minds.
This could be costly if the variety is susceptible to
diseases or nematodes that may also be present."
An Arkansas Agricultural Experiment Station cultivar
screening program supported by the Arkansas Soybean
Promotion Board provides information producers need
to know about disease resistance. Screenings this year
revealed problems with stem canker and new hope for
root knot nematode infestations.
"A greater number of varieties in our stem canker
screen are showing susceptibility than in past years,"
Kirkpatrick says. "This may be because there are lots
of new varieties in the screen, but many of the transgenic
and conventional varieties are showing susceptibility.
"When producers look for a Roundup-Ready variety, they
need to be sure they find one that also has any disease
resistance they need," he says. "It would be a shame
to have a nice weed-free field only to see the plants
die because they were susceptible to disease."
Screenings also found some promising varieties for
resistance to root knot nematode.
"This has been a good year for screening because dry
weather shows root knot nematode damage more readily,"
Kirkpatrick says.
Bob Riggs, U of A nematologist, says nematodes infest
a plant's root systems and distort the vascular tissue
that transports water and minerals through the plant.
"The distortion impedes the movement of water through
the plant," Riggs says. "In a wet season, or with irrigated
fields, soybeans have the ability to resist or recover
from damage. Non-irrigated soybeans in a dry year will
show yellow spotting and stunting in the field that
can result in considerable yield loss."
The Division of Agriculture screening program has identified
a number of Group V soybean varieties that are resistant
to root knot and soybean cyst nematodes.
"Several Group IV soybeans were included in the screening
this year," Kirkpatrick says. "The majority of Group
IV varieties are susceptible to root knot nematode,
but we're finding a few that have some resistance.
"Caution is still the word for producers planting
Group IV varieties," he says.
Before choosing any variety, producers need to know
what nematode populations may be present in their fields.
"Fall sampling, after harvest, is a cheap and easy
way to see if you need a resistant variety," Kirkpatrick
says. "If I were a producer, it would be my goal to
sample every field this fall before I selected any variety.
Nematode populations are typically highest in the early
fall."
Once producers know if nematodes or diseases are in
their fields, they can find information about disease
resistant varieties on the Division of Agriculture's
SOYVA system or from county Cooperative Extension Service
agents.
"The day you plant a crop is the last day you can
do anything to protect against most of our most serious
diseases and nematodes," Kirkpatrick says. "If you don't
use all the available information about varieties to
make your selection, you may be in for an unpleasant
surprise."
Soybeans Today January 2000
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