Weed control has been a part of agriculture ever since hunter-gatherers became farmers about 6,500 years ago. With that, Phil Stahlman, weed scientist at the Kansas State University Agricultural Research Center-Hays, offered a short history of weed control at Sorghum U, Jan. 12, at Hays, Kansas.

“Those first farmers pulled weeds by hand,” Stahlman said. “Likely that was women power, followed by horses pulling equipment such as a plow. It wasn’t until the early 1700s that we first had modern husbandry, such as Jethro Tull in 1731 advocating planting in rows in order to allow horse hoeing.”

Not much changed with tillage until the early 1900s when tractors took over for horses. Perhaps the first chemical treatment to stop weeds was salt, as used by the Romans, Stahlman said.

“It was used primarily for military purposes, to salt the fields of the Romans’ enemies,” Stahlman said. “Eventually, they learned to use salt in orchards, but it wasn’t until much later that we have herbicides.”

The modern day of chemical treatment of weeds came in the early 1940s with the discovery of chlorophenoxy acetic herbicides such as 2, 4-D and MCPA for broadleaf weeds. These products, Stahlman said, could risk crop injury if not delivered in a timely manner.

“Those discoveries started the crop protection industry,” Stahlman said. “Over the next three to four decades, quite a number of products were introduced.”

Most of the common modes of action were developed and products like Aatrex, Lasso, Bladex, Dual, Ramrod and others appeared. In the 1960s, Bill Phillips, the chief of KSU-ARCH at the time, developed the wheat-sorghum-fallow rotation principle that featured the herbicide atrazine after wheat harvest while planting grain sorghum the following spring.

“It reduced the swings we saw in yields and reduced soil erosion dramatically,” Stahlman said. By 1992, 96 percent of the U.S. sorghum acreage had been treated with one or more herbicide.

Today’s challenges

There are challenges to sorghum weed control, Stahlman said, such as limited availability of herbicide options, risks to re-registration of atrazine and its replacement with more expensive and less effective products.

“If (atrazine failed to be re-registered), we would lose most of the foundation herbicides we currently use on sorghum,” Stahlman said. “It’s my hope that because of atrazine’s importance, particularly to soybeans and corn, that I doubt EPA will ban it.”

Herbicide resistant weeds have emerged as a problem, Stahlman said, with Palmer amaranth, waterhemp, horseweed and kochia becoming the most prevalent weeds for resistance, primarily to glyphosate, but also to multiple modes of action. Palmer amaranth, in particular, is coming on with a vengeance. That means farmers can’t put much pressure on any new products to perform.

“We know the PPO herbicide family is also prone to develop resistance,” Stahlman said. “It just hasn’t done it yet in Kansas. If we put much pressure on them, we’ll have resistance to them also.”

Larry Dreiling can be reached at 785-628-1117 or ldreiling@hpj.com.

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