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 representative.

“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 per day.

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 generation.”

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 Barnett.

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.