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Late-season Weeds Underscore Need for More Residual Herbicides

Late-season Weeds Underscore Need for More Residual Herbicides

Weed breakthroughs obvious at harvest in some fields.

Ask Betsy Bower about the worst crop problems for 2014, even though it was a favorable year overall for most crop producers, and it isn't long before she gets around to weed control. Bower is an agronomist with Ceres Solutions based in west-central Indiana.

"We saw several cases where weeds broke through later in the season," she says. "Farmers ought to rethink their weed control program if they saw late-season weeds. We may need more residual herbicides in the program to prevent weeds from breaking out late in the year."

Tough customer: Give it an inch and Palmer amaranth will take a mile. This stand of weeds was taking over even by mid-season.

Some weeds may have broken out early enough to affect crop yields. Others were a problem for combining at harvest. Some makes of combines handle particular weeds better than others.

Related: Scout for Weeds from the Combine Seat

The problem, Bower says, is that some weed that are most troublesome today can continue germinating later into the season than weeds that most farmers battled in the past.

Palmer amaranth, the 800-pound gorilla in the weed world, is an example. Most prevalent in northeast Indiana but now showing up in pockets all over the state, it can germinate late into the season. And once it germinates in as little as 30 to 40 days, depending on weather conditions, it can produce seeds. This plant will produce mature seeds even before its seedhead has grown as far as it will finally get.

Related: It Pays To Scout Fields Before You Harvest

Seedheads on Palmer amaranth plants can grow up to 20 inches long, or even longer. However, they can begin producing mature seeds which can reproduce while the seedheads are still much shorter.

Many of the more troublesome weeds today, including Palmer amaranth and tall waterhemp, are resistant to glyphosate herbicides. Several weeds are also resistant to other herbicides as well. Many weed control specialists suggest assuming that if you have a weed like Palmer amaranth or tall waterhemp in your vicinity. It is glyphosate resistant. This means that residual herbicides in your weed control program are even more important.


In the coffee shop, it is known as Palmer pigweed. In university circles, it is referred to as Palmer amaranth. Whatever you want to call it, this weed is the No. 1 weed to watch. Stay on top of your control plan with our new free report, Palmer Amaranth: Understanding the Profit Siphon in your Field.


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