D22-Lancaster Farming Saturday, December 8,1990
WASHINGTON. D.C.
“Cocktail time” is fast approach
ing for crop-hindering weeds, but
few of them are likely to survive
the party.
Roy J. Smith Jr., an agronomist
with the U.S. Department of Agri
culture’s Agricultural Research
Service, has been studying the
“cocktail” approach to weed con
trol, blending chemicals and
natural weapons such as fungi to
solve multiple problems in a
single sweep.
Smith doesn’t invent the ingre
dients; those come from commer
cial manufacturers and research
laboratories, and include both
commercially available herbicides
and experimental materials.
His specialty is the combina
tions. Using fungi and herbicides,
he’s blended substances capable
of hitting two weeds at once, and
one blend even goes after three.
While Smith works primarily in
rice, he says there’s no reason why
similar combinations can’t be
organized against weeds in other
crops. And he emphasizes that the
combinations aren’t creating
brand-new weapons simply
blending two that can co-exist
peacefully as each goes about its
business of fighting weeds.
A basic ingredient in Smith’s
recipes is a form of the fungus
Colletotrichum gloeosporioides,
marketed by Ecogen Inc. of Lang
home, Pa., as College. An ounce
of the fungal spores about 78
billion spores per acre will
wipe out northern jointvetch, a
major weed in rice fields.
“Northern jointvetch makes
little black seeds that get into the
rice, so farmers are paid less for
their rice,” said Smith, who works
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Crop Weeds Face Deadly Combinations
at the Rice Production and Weed
Control Research unit operated by
ARS at Stuttgart, Ark. “We had
other weeds we needed to control,
too, so we started looking at possi
ble combinations of fungal patho
gens and herbicides that would be
environmentally safe.”
One of the early finds was a
fungus that attacks winged water
primrose, an aquatic weed in rice.
Researchers were able to grow the
fungus in the laboratory, put it in
rice fields and wipe out the weed
using only an ounce of spores per
acre. Best of all, it mixed well
with the fungus that attacks north
ern jointvetch.
“It looked really good in
research,” Smith said. “But there
was one problem winged water
primrose isn’t prevalent enough to
justify a company developing this
commercially. Perhaps, in the
future, if this weed becomes a big
problem, someone might recon
sider this.”
Hemp sesbania, on the other
hand, is a big enough problem to
attract major herbicide company
attention. Seen in both rice and
soybean fields, hemp sesbania,
like northern jointvetch, sullies
the harvest with little black seeds,
resulting in lower payments for
the crop. Hemp sesbania and
northern jointvetch are considered
“companion weeds,” since they
like the same type of environment
and often infest the same fields.
The chemical acifluorfen is
commonly used to control hemp
sesbania, but does little to block
northern jointvetch. Smith discov
ered that acifluorfen can be
applied in conjunction with the
fungus against northern joint
vetch, and that combination now
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is used by farmers.
Similarly, bentazon, the chemi
cal used against the aquatic weed
redstem, also works well in com
bination with the fungus, Smith
said.
“You’re not as likely to see all
three of these weeds northern
jointvetch, redstem and hemp ses
bania in one field, but if you
do, we’ve even developed a three
way mix that gives good control of
all three," he said.
The next, and tougher, step is
finding a fungicide that fights crop
diseases without also wiping out
the northern jointvetch-fighting
fungus, Smith said.
“The amount of rice that’s
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treated with a fungicide has
increased tremendously in the last
seven to eight years,” he said.
“But the main one used is
benomyl, and it’s quite injurious
to C. gloeosporioides, As it stands
now, a farmer has to choose
between using the fungus for his
weeds or a fungicide for crop dis
eases.”
One promising newcomer is a
fungicide called iprodione. Smith
said it can’t be applied at the same
time as the beneficial fungus, but
the fungus can survive in a field
treated earlier with iprodione.
Even more encouraging is an
experimental fungicide called
pencycuron. According to Smith,
■MC.
this can be mixed directly with C.
gloeosporioides without injuring
the fungus. “It’ll be a pretty good
step forward when it’s approved
for use on rice,” he said.
“We also hope to find other
natural fungi like the one that
attacks winged water primrose,”
Smith said. “I think they’re out
there somewhere for most of our
major weeds in rice, particularly
the aquatic weeds.
“We are constantly researching
ways to produce and improve
weed control strategies that pro
tect the environment. I think these
types of mixes are among the most
promising,” he said.
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