Defend Your Yield

Is weed pressure in your area lighter than it was five years ago? Across the country, the answer is no, including in Larry Steckel's region.

"The coffee-shop talk around here focuses on two topics every day - pigweeds and politics," says Steckel, Ph.D., an extension weed specialist with the University of Tennessee. "When glyphosate isn't effective at controlling weeds of any height, you know life is never going to be the same again."

"When glyphosate isn’t effective at controlling weeds of any height, you know life is never going to be the same again."

Steckel notes that weed control in Tennessee had seemed straightforward until 2005. "In year one, there were a few weeds, such as waterhemp or Palmer amaranth, that were surviving in farmers' fields," Steckel says. "By year two, bigger patches of weeds persisted. By year three, the weeds were so thick that some growers couldn't run a combine through their fields."

Since then, growers have been spending up to $100 an acre on herbicides for soybeans and $60 or more for corn. They also hire chopping crews, which adds another $20 to $25 per acre. "Even then, we're still not getting the weed control we'd like," Steckel says. These challenges aren't confined to the South, he adds. "Right now, growers in Missouri, Illinois, Iowa, Indiana and beyond are in the similar situation we were in right before the big blow up in 2008, when it became nearly impossible to control weeds, such as waterhemp."

Start Clean, Stay Clean

A recent University of Illinois study suggests that it's a question of when, not if, Palmer amaranth will become established in the state. "We're on the threshold of a major Palmer amaranth outbreak," says Aaron Hager, Ph.D., an associate professor of weed science at the University of Illinois.

Soybean yield losses approaching 80 percent and corn yield losses exceeding 90 percent from Palmer amaranth have been reported in peer-reviewed scientific literature, Hager notes. "We typically don't lose entire fields to weeds, such as waterhemp, but Palmer amaranth will be a game changer."

A grower's best defense against Palmer amaranth (which can grow 3 inches or more per day) and many other yield-robbing weeds is an early-season weed management system, says Gordon Vail, Ph.D., a technical product lead at Syngenta. "When you take a preventive approach, you've got a fighting chance of controlling weeds before they become a problem."

The best weed is the one that never germinates, adds Hager, who is a strong proponent of pre-emergence herbicides. "Try to stop problems before they start, because the most competitive weeds are the ones that come up with the crop. The window of how long the crop can compete with weeds without yield loss is pretty small."

In areas where glyphosate resistance has taken hold, the lack of a pre-emergence system can transform small weeds into big headaches, Steckel says. "Once the weeds got 3 or 4 inches tall, growers around here had to disk up their fields and replant."

Early-season weed management can prevent this scenario while offering many other benefits, including:

• Fewer deposits in the weed seed bank. Pre-emergence products offer growers a fighting chance to control weeds throughout the growing season. The seedling stage is the most vulnerable time in a plant's life, making small weeds easier to kill than large weeds. "If you're diligent about controlling weeds right from the start, you can control the weed population," Vail says. "You not only reduce weed competition, but you also reduce the number of weeds your post-emergence product has to control."


• Greater peace of mind. In farming, few things go exactly as planned. "If it rains a lot, for example, a pre-emergence product gives you more flexibility with your post-emergence application," Vail says.


• Delayed development of herbicide resistance. "Controlling weeds early in the season generally means targeting smaller weeds," says Bryan Ulmer, Ph.D., Syngenta global technical manager for herbicides. "Most herbicide options are more effective on germinating and small weeds. Good examples are populations of waterhemp and Palmer amaranth (often already resistant to one or more modes of action), which become very difficult to control if you let them grow more than 3 or 4 inches. Early-season weed management helps maximize efficacy and minimize the escapes that can lead to increased tolerance and ultimately resistance in populations.''


• Higher yield potential. Years of research in corn have shown that growers harvest higher yields when they incorporate an early-season weed management program, rather than using a total post-emergence program. "By starting with clean fields, growers can maximize yield potential and reap the full benefits from the significant investments that they are making in their crop," Ulmer says.

Pre-emergence products aren't just for corn. Early-season weed management with pre-emergence herbicides in soybeans plays an important role in reducing weed competition, decreasing the number of weeds that need to be controlled post-emergence and providing mode-of-action diversity in managing herbicide resistance, says Don Porter, a technical product lead for Syngenta. "With glyphosate resistance becoming more widespread, growers are realizing that early-season weed management with pre-emergence herbicides offers a good return on investment in soybeans."

Get a Jump on Weeds

The foundation of any effective early-season weed management program needs to start with a robust pre-emergence product. Lexar^® EZ or Lumax^® EZ herbicides from Syngenta offer multiple effective modes of action to manage herbicide resistance issues in corn, Vail says. Lumax EZ, for example,

contains Dual II Magnum^®, Callisto^® and AAtrex^® 4L herbicides to provide broad-spectrum, effective weed control.

In soybeans, Prefix^® pre-emergence herbicide offers a mix of Dual Magnum and Reflex^® herbicides and provides up to five weeks of control on Palmer amaranth, waterhemp and other driver weeds. Its long residual control allows for a wider application window, reducing the risks associated with applying glyphosate too early or too late. Boundary^® 6.5 EC soil-applied herbicide is another option in soybeans. It delivers early-season grass and broadleaf weed control, excellent resistance management and rotation flexibility. By using Boundary, growers can extend the post-application window up to five weeks after planting, thereby protecting yield and keeping fields cleaner longer.

As a leader in early-season weed management solutions, Syngenta is also developing a new active ingredient (bicyclopyrone) for corn. Upon registration, it will be part of a four-active-ingredient herbicide premix that will provide three different modes of action for sustainable control of waterhemp and Palmer amaranth, as well as improved control of large-seeded broadleaf weeds, such as common ragweed, giant ragweed and cocklebur. "Bicyclopyrone will raise the bar on weed control in corn, particularly for large-seeded broadleaf and tough-to-control weeds," Ulmer says.

Syngenta is also developing other products that will become important tools for weed control and resistance management. Callisto GT, a post-emergence premix of Callisto and Touchdown^® herbicides for corn, can be tank mixed with atrazine and will be available for the 2014 growing season, Vail says.

All these options allow growers to incorporate various modes of action for sustainable, early-season weed management. Although weed control is becoming more complex, the results are worth the effort, Hager says. "In the end, it's about maximizing yields. We can be successful if we adopt a new mindset of controlling weeds upfront and realize that this is a long-term investment."