How To Control The "King Kong of Pigweeds"

Focusing on a weed that's new to Iowa, Palmer Amaranth, last week's field day was well-attended.

Published on: Oct 4, 2013

Iowa farmers need to be on the lookout for Palmer Amaranth, a weed that has caused a lot of problems for many years for farmers in the southern United States. Clarke McGrath, an Iowa State University Extension field agronomist in western Iowa, reports that an ISU-sponsored field day was held last week in his area, focusing on how to correctly identify and manage Palmer Amaranth. The field day was well-attended.

Palmer Amaranth is a hard-to-control weed that in recent years has been marching north and has been found in Illinois, Missouri and Nebraska. It was recently confirmed for the first time in Iowa, having been found and positively identified by ISU weed specialists. It was found in a field near the Missouri River in Harrison County in August. This weed is a relative of pigweed and can be easily confused with waterhemp.

TOUGH CUSTOMER: Palmer Amaranth is a hard-to-control weed which in recent years has been marching north from the southern U.S. and has been discovered in fields in Illinois, Missouri and Nebraska. It was recently confirmed for the first time in Iowa, having been found and positively identified by ISU weed specialists in western Iowa near the Missouri River.
TOUGH CUSTOMER: Palmer Amaranth is a hard-to-control weed which in recent years has been marching north from the southern U.S. and has been discovered in fields in Illinois, Missouri and Nebraska. It was recently confirmed for the first time in Iowa, having been found and positively identified by ISU weed specialists in western Iowa near the Missouri River.

Having seen Palmer Amaranth in the southern U.S. is one thing, but seeing this weed thrive here for the first time is unsettling

McGrath says, "Thanks to Rich Pope, Extension director in Harrison County, for putting together a great field identification and management field day on Palmer Amaranth--the 'King Kong of Pigweeds'-- as coined by Western Iowa Co-op's Randy McDunn. "We had a great crowd of growers, seed dealers, ag retailers and chemical manufacturer representatives -- I'd guess the crowd represented half a million acres or so."~~~PAGE_BREAK_HERE~~~

Having seen Palmer Amaranth in the South was one thing, but seeing it thrive in Iowa fields was unsettling, says McGrath. As several weed scientists from land grant universities around the Midwest have said in public, it's not a matter of "if" but "when" we will be battling this weed in many of our fields. "I put together a quick identification sheet with some Palmer Amaranth information and management tips," says McGrath. "It is short and many of the bullet points are designed to elicit conversation, so that's why they are followed by question marks. It is attached to this article. Also, Rich Pope put together a tremendous ID sheet that's attached."   

Early yield reports: initial reports indicate yields are better than expected in a number of Iowa fields

One way to describe the initial yield reports this fall -- yields are better than expected. "I wanted to say the early yields are 'amazing,' says McGrath. "Because given the rough growing season we had this year, yields are indeed amazing. But it is really early and I don't want to set expectations too high."

 "We are at around 5% corn harvested across Iowa compared to a five-year average of 16%, and 5% on beans compared to an average of 21% at this time. "Remember that often these early harvested fields were the fields we could get planted earlier as well, which typically means our better soils," says McGrath. "Regardless, while there have been some tough-yielding and disappointing fields, there have been a lot of impressive numbers coming in, too. A few numbers from the area:

* Kimballton area, multiple fields of beans averaging 56 bushels per acre; Avoca area, reports of beans in the low to mid 50s. Corning area, corn plot averaging 219 bushels per acre at 19% moisture.

* Carroll County 156 bushels per acre of corn -- this was reported around 20 bushels per acre below average for this farm. Also another couple of whole field averages, one at 135 and another at 175.5 bushels per acre. A field near Dedham, a very dry area, went 110 bushels per acre; APH for this field is 175 bushels. In Guthrie County, some beans were planted mid-May that never got very tall went 46 bushels per acre. In Taylor County a cornfield yielded 159 bushels per acre.

Remember, "these are the early reports," notes McGrath. "And while what we agronomists hear early is usually a little less fluffed than coffee shop yield reports, there is often a significant fluff factor. But, these are better numbers than many of us expected even with the fluff taken out, so here's to hoping the good news continues."