October 22, 2008 -
Imagine a recurring nightmare in which an army of goblins slowly robs
you of your money and eventually your livelihood and whose numbers
multiply no matter what you do to stop them.
Day after day, Georgia row-crop farmers are dealing
with something eerily similar -- and so will Alabama growers unless some
solution is found.
“For farmers, it's actually scarier than Halloween,”
says Dr. Mike Patterson, an Alabama Cooperative Extension System weed
scientist and Auburn University professor of agronomy, who has been
closely monitoring the rapid progression of the weed.
goblin, in this case, is herbicide-resistant Palmer amaranth, better
known as pigweed.
Desperate to contain its spread, farmers already have hand pulled
resistant pigweed off some 15,000 acres of Georgia cropland.
“Workers are pulling up the entire plants -- root
and all -- out of the ground and loading them on a wagon, then piling
them up on the edge of the field,” says Patterson.
As farmers have discovered through experience, mere
chopping isn't enough. Only root-and-shoot removal will work --
otherwise weeds return with a vengeance as new plants sprout from the
Patterson's Georgia counterparts estimate that more
than a million acres of cropland are infested with the resistant weeds,
which are spread not only through seed but also via pollen.
Why are farmers so frightened of this weed? By
developing resistance to the standby herbicide glyphosate, commonly
known as Roundup, pigweed has dethroned the system farmers have relied
on for roughly a decade to control weeds and, equally important, to
contain operating costs.
This system, a combination of chemistry and crop
genetics, allowed farmers to spray glyphosate, directly over the cotton
plants, killing a wide range of weeds while sparing the cotton plants
and also relieving them of costly tillage and other herbicide
For cotton producers, the only other option is using
soil-applied herbicide to kill the pigweed before it emerges. But even
this doesn’t guarantee of success.
To work, the herbicides must be activated by
rainfall; otherwise, they don't work. And if they don't work, the
pigweed ultimately emerges and out-competes the cotton.
“By the time the cotton reaches 3 or 4 inches,
you've got pigweed that is 7 or 8 inches.”
By then, it's too late, he says.
“Beyond that, there's nothing available in our
cotton herbicide arsenal to kill the weed postemergence.”
In a classic case of survival of the fittest, the
weeds outgrow cotton plants, robbing them of moisture and vital plant
nutrients, slowly starving them.
One of the only remaining options is rotating cotton
with corn. As a grass crop, corn will tolerate applications of
herbicides that broad-leafed crops such as cotton won't, he says.
For example, pigweed still can be controlled using
corn herbicides such as atrazine, which farmers have used for 40 years.
“Almost every acre of planted corn is treated with
atrazine,” says Patterson, adding that a couple of other corn-related
herbicides are also still effective in treating resistant pigweed.
University of Georgia researchers already are
working with U.S. Department of Agriculture counterparts to identify
other ways to attack the weed. They've discovered that pigweed seed may
typically degrade after only three years in the soil.
“That may be one of the weak points of this weed,
which is a good thing,” Patterson says, adding that other weed seed,
such as sicklepod and morningglory, may survive for decades in the soil.
Researchers are searching for ways to keep these
fields clean -- managing them so that germination doesn't occur, leaving
pigweed seed to decay in the soil.
“That's the only way we're going to beat this thing,
unless chemical companies come up with another weed control system
similar to the Roundup approach,” says Patterson.
“But don't hold your breath on that one, because
Roundup represented a once-in-a-lifetime discovery that is not likely to