Stoneville, Mississippi
March 1, 2007
By Robert H. Wells, Delta
Research and Extension Center
Research has determined a method to control one of the most
common and troublesome weeds of Mississippi rice production --
Amazon sprangletop.
“Amazon sprangletop is an annual grass that complicates
Clearfield rice production, a system designed to combat red
rice,” said Jason Bond, a
Mississippi State University rice weed scientist at the
Delta Research and Extension Center in Stoneville. “Newpath, an
herbicide labeled for use in Clearfield rice, normally provides
good control of barnyardgrass and red rice, but it has performed
very inconsistently on Amazon sprangletop.”
Bond said newer Clearfield varieties (CL171, CL161 and CL131)
have increased tolerance to Newpath compared to older Clearfield
varieties. That tolerance allows growers using the Clearfield
system to apply two applications of Newpath at up to 6 ounces
per acre to manage difficult grasses.
However, in research during 2006, Bond found that Clearfield
rice growers can manage Amazon sprangletop with only 4 ounces
per acre of Newpath if they add a residual herbicide. They must
apply the combination prior to rice and weed emergence and then
follow up with a second Newpath application at 4 ounces per acre
when rice reaches the four-leaf development stage.
The rice weed scientist found residual herbicides Prowl H20,
Prowl EC and Command worked best with this method.
“Newpath plus Prowl H20 or Prowl EC controlled Amazon
sprangletop 95 percent of the time in 2006 and were the least
expensive,” Bond said. “However, some injury to the rice may be
observed following a Prowl application. Also, if the rice crop
fails for some reason, rice cannot be replanted in a field where
Prowl has been applied the same year.”
Bond said if a Clearfield rice producer has concerns about
injury or the possibility of replanting, and Amazon sprangletop
is not already present, then Command, which provided 85 percent
control, will be the next most economical treatment.
Clearfield growers who initiate herbicide applications at
pre-emergence to control Amazon sprangletop could save nearly
$16 an acre on Newpath compared to efforts made after the weeds
and rice emerge.
“Sometimes factors such as sudden rains, high winds or more weed
growth than expected, will leave growers no choice but to apply
their herbicides postemergence,” Bond said. “If this happens,
Clearfield producers should consider increasing the Newpath rate
to 6 ounces per acre for Amazon sprangletop control.”
Bond said in 2006, a postemergence application of Newpath at 6
ounces per acre provided around 80 percent control of Amazon
sprangletop when tank mixed with Prowl EC, Prowl H20 or Command
and then followed up with a second 6 ounce per acre Newpath
application at the four-leaf stage.
Bond also evaluated barnyardgrass and red rice control in the
Clearfield system. The researcher achieved control of both
annual grasses with all Newpath timings, rates and residual
herbicides.
Mississippi rice producers planted nearly a third of the state’s
rice acreage to the Clearfield system in 2006.
Growers’ check-off dollars from the Mississippi Rice Promotion
Board sponsored Bond’s research.
Nathan Buehring, the MSU Extension rice specialist based in
Stoneville, said water is important when using residual
herbicides in rice production.
“The key to making residuals work is water, meaning that if you
apply a residual herbicide, and it does not rain within a couple
days, it needs to be flushed,” Buehring said. “With no rain or
water, the residual herbicide is less effective because weeds
emerge before the herbicide is activated, or the residual
herbicide will degrade over time. Timely rainfall events or
flushing will be needed to keep residual herbicides working.”
Buehring agrees that sooner is better than later when
controlling weeds.
“Grass control is cheaper, easier and results in higher yields
if it is done early instead of late in the season,” Buehring
said. “Every day that grass is out there competing with rice, a
yield loss is occurring. It can be small or big, depending on
the grass density.” |
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