Global Agriculture

Effective weed management tops considerations for maximizing soybean yield potential

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28 January 2021, USA: Soybean growers across the U.S. have been evaluating their 2020 crop yields to make input decisions for next season. Seed selection is often made first; and with more trait options available this year, Syngenta knows growers are facing the challenge of selecting corresponding herbicides that can best protect their seeds’ full genetic yield potential.

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Syngenta recently spoke to university agricultural researchers who reinforced the importance of a strong weed resistance management plan and explained the impact such a plan can have on soybean yield potential.

“Having the best crop genetics is like having the keys to a fast car,” said Sarah Lancaster, Ph.D., assistant professor and extension specialist at Kansas State University. “Agronomics and fertility are like the gas in the tank. Having weeds is like having a leak in that tank.”

A key method for maximizing yield potential is to use a combination of cultural and chemical practices to effectively manage weeds and prevent them from going to seed. This means choosing practices such as tillage and narrow-row spacing along with a full-season herbicide program that contains multiple effective sites of action.

Prashant Jha, Ph.D., associate professor and extension weed specialist at Iowa State University, suggests such an integrated strategy that combines herbicide and cultural approaches. “To delay or manage herbicide resistance, integrate some of the cultural strategies, like high seeding rates, reducing row spacing to promote early canopy closure and use of cover crops in integration with herbicide programs. Full rates of herbicides, multiple effective sites of action and a combination of soil residual herbicides are the strategies to go with.”

This year, growers have even more choices to make as new traits are available for planting. “In recent years, new traits have come to market that provide growers even more options for rotating their herbicides to new effective sites of action,” said Pete Eure, Syngenta herbicide technical lead. “The Syngenta portfolio of soybean herbicides can be used regardless of the trait system — from burndown through post-emergence. This gives growers the flexibility to choose their herbicide based on product performance and agronomic value for their specific field, all in combination with sound cultural practices.”

When developing a weed management program, growers should consider the value their inputs make on their bottom line.

“So many folks are focused on cost per acre with weed control,” said Bill Johnson, Ph.D., professor of weed science at Purdue University. “They really need to think about it in terms of cost per bushel.”

In fact, studies indicate that for every day growers are late with their herbicide application beyond the critical period, they lose as much as 1% of their soybean yield*. “There’s a period of time, which we call the critical period, when the plant is most susceptible to emerged weeds in terms of yield loss,” said Clarence Swanton, Ph.D., professor emeritus at the University of Guelph, Canada. “The earlier the weeds emerge and the smaller the crop, the greater the impact.”

Eure agreed. “The way to maximize your yield potential is to have the flexibility to use the right products applied at the right time to deliver the best results locally,” he said.

Growers should also anticipate what effect the actions they take now will have on future crop yield, and minimizing herbicide resistance can be a good place to start.

“If weed management is a battle, preventing additions to the soil seed bank effectively reduces the size of the opponent’s forces, giving the farmer the upper hand,” Lancaster said.

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