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Palmer Amaranth Continues Northward Spread


Many, many years ago – not too long after I started covering the agricultural marketplace – one of my first trips was to central Arkansas. There, while visiting a corn farm, I chanced across a huge plant in one of the crop fields I was in. “That sure looks healthy,” I casually remarked to the grower I was interviewing. “That,” he said before ripping the plant out of the ground, “is a pigweed, and from the looks of it, one that can’t be killed anymore by the chemistry I’m using here.”

Since that first encounter with pigweed, more commonly known as Palmer amaranth, this once “scourge of the South” weed variety as steadily advanced further northward with each passing crop season. In fact, as of the end 2015, 25 states across the country now report the presence of Palmer amaranth plants in their crop fields. Even more troubling, a good portion of these have developed resistance to many of the industry’s most popular herbicide control products, including glyphosate.

“We did a common garden study in Southern, Central, and Northern Illinois to ask if different varieties of Palmer amaranth from the south complete their life cycle in all three locations and cause yield loss in soybean,” said Adam Davis, a Weed Ecologist at the University of Illinois. “The short answer is yes: There are no current climate limitations to any of the genotypes that we looked at. This is a serious weed.”

Furthermore, the yield losses are staggering. For example, while its cousin weed, tall waterhemp, can cause 30% yield loss when it is present in soybean fields in great numbers, Palmer amaranth’s presence can lead to up to 80% yield loss.

And observers think the Palmer amaranth situation could get much worse in 2016. As many industry insiders pointed out at the recent 2016 Commodity Classic show, 2015 was an exceptionally wet year for many of the Midwestern states. “This could have caused flooding across fields and moved some of the Palmer seeds into new territories than they’ve ever been in before,” predicted Dave Johnson, Product Development Manager for Soybean Herbicides at DuPont Crop Protection.

Experts all shared the same advice to curb Palmer amaranth’s spread: Ag retailers and their grower-customers should continually scout their fields for the weed and use different herbicides with multiple modes of action to keep it in check as best they can. The University of Illinois’ Davis also recommends diversifying cropping systems to include winter annuals and being extra careful when cleaning equipment, especially if it’s been purchased from out of state.

“[Palmer amaranth] can complete its life cycle in a very short period of time,” he said. “Even if you killed early season populations, if it comes up again in late summer, it can still produce seed by harvest time.”

Source: Eric Sfiligoj, CropLife

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