WEST LAFAYETTE, Ind. — The Indiana Seed Trade Association
hosted a luncheon that included a presentation on the impact of Palmer amaranth,
an invasive weed species that has reached Indiana.
The weed is difficult to manage, so precautions must be
taken to prevent yield reduction in corn and soybean fields.
“Prevention and early detection are really important — be
really be proactive,” advised Kelly Barnett, DuPont Pioneer field development
“In 2012, it showed up in Indiana. I wasn’t surprised to see
it show up in Evansville because that was the pattern, but to see it show up in
northwest Indiana was a little surprising. In 2013, it showed up in about 24
counties across the state — that’s how quickly it spreads.”
Barnett predicted that it won’t be long before every county
in Indiana has to deal with the weed. She described Palmer amaranth as an almost
perfect weed in terms of survival and hardiness.
“A lot of weed scientists like me would say, if you could
paint the picture of a perfect weed, Palmer would just about be it,” she said.
“It has high seed production. It produces hundreds of thousands of seeds, up to
well over a million.”
A study at the University of Arkansas discovered that a
female Palmer plant produces more than 1.7 million seeds, Barnett said. Because
the seeds are so small, they can easily be easily transported.
Palmer amaranth also has a deep taproot, making it easy to
store nutrients and water. The plant is drought resistant and survives in high
humidity. “It is very competitive with the crop,” Barnett said. “It has the
highest photosynthetic rate of any weed or crop that has been tested to date.
This is why it’s so efficient at being able to grow and compete. It’s actually
has a photosynthetic rate that is twice that of corn or soybeans.”
Because of the high photosynthetic rate, the weed can grow
two to three inches per day in hot temperatures, such as those in southern
states. In Indiana, Barnett estimated, it could easily grow one to two inches
The weed also has high resistance to herbicides and can
easily adapt to chemicals.
“It has separate male and female plants,” the field
development representative explained. “If you have a male plant that is
resistant and a female plant that is not, the offspring will be resistant. You
can see how quickly resistance traits can be passed on generation to
The combination of these factors makes Palmer difficult to
manage, particularly in soybeans, Barnett said.
The first step farmers can take in fields that have had
Palmer amaranth is to use a pre-emergence application on every acre.
“In Indiana, we got away from that when Roundup Ready came
out. We didn’t need pre applications,” Barnett said.
Farmers also can use timely post-emergence applications,
including herbicides such as Blazer, Cobra and Flexstar. Post-emergence
applications often are more difficult and less successful, however, according to
Other weed management techniques include deep tillage, which
pushes seeds deeper making it harder for them to emerge.
“Rotating soybeans with corn is a really effective tool if
you use it wisely,” Barnett added. “Hand-chopping weed is another option.
“Nobody likes it, but if you really want to manage this
weed, you might need to.”
Cover crops, particularly cereal rye, also are a good tool
to manage the weed.
For more information on ISTA, visit www.indianaseed.org.
Helpful information regarding Palmer amaranth is available through Purdue
Extension at www.extension.purdue.edu/extmedia/WS/WS-51-W.pdf.