In Roundup Ready soybean crop Morningglories decorate roadside ditches with their bright flowers, but farmers don't look kindly on them in their soybean fields. Their tenacious, clinging vines choke both yields and combines, making harvest difficult.
If allowed to grow all season, just two morningglory weeds per foot in a soybean row can reduce yields up to 40 percent, said Dick Oliver, a University of Arkansas agronomy professor. "They also cause harvesting problems because their vines get tangled in the combine head," Oliver said. As a result, season-long morningglory control is a high priority for farmers.
"Morningglory tends to be a big problem across the southern United States," said Dan Poston, assistant Extension soybean specialist at Mississippi State University's Delta Research and Extension Center. "It is a large-seeded broadleaf weed that continues to emerge and germinate throughout the summer growing season."
This tough weed causes problems even in Roundup Ready soybeans, which account for roughly half the soybean acres in the South.
"Without a tank-mix partner, Roundup herbicide has not provided adequate morningglory control," said Todd Hampton, retail manager for Royster Clark in Union City, Tenn.
To effectively control morningglory with Roundup, Oliver recommends spraying the weed during the one- to two-leaf stage. However, weather conditions and other field work can make appropriate spray timing difficult, which may account for the reduced control seen in Roundup Ready soybeans.
A standard Roundup Ready soybean program requires two applications of Roundup herbicide, Oliver said.
"In my work, I've seen pitted and entireleaf morningglory escape one application," he said. "The second application of Roundup will either control it or stunt it so badly that it never comes through the canopy."
However, adding another herbicide to Roundup often sharpens morningglory control and may eliminate the need for a second application of Roundup. A tank-mix also can improve control when rains allow morningglory flushes to grow beyond the two-leaf stage before they can be sprayed. In some cases, fields with intense morningglory pressure may require two applications of the tank-mix.
Hampton, whose dealership includes a custom application business that covers 20,000 to 25,000 acres per year, recommends FirstRate herbicide as an ideal tank-mix partner for controlling morningglory.
"We mix a half-rate of FirstRate with one quart of Roundup," he said. "I believe it's the best partner for Roundup when trying to control morningglory. I have also seen better control of smartweed, velvetleaf, sicklepod and giant ragweed with this tank-mix."
Tank-mixing Roundup with a product such as FirstRate brings several advantages to a Roundup Ready soybean system. Research by Oliver and Poston indicates that FirstRate enhances weed control without damaging the crop. In addition, it extends the application window and prolongs residual control.
In 1998, Oliver's Arkansas field trials showed that a half-rate of FirstRate and one quart of Roundup provided an average of 86 percent control of entireleaf and pitted morningglory, two of the many similar species in the morningglory family. One application of 1.5 pints of Roundup controlled only 43 percent of those weeds, while two applications of Roundup of one quart followed by 1.5 pints offered 70 percent control.
"The tank-mix of FirstRate and Roundup does a nice job on morningglory," Oliver said. "In my work, it consistently provides better morningglory control, which makes it a good fit in this area. Another advantage is the lack of injury with FirstRate." In his studies, a tank-mix of FirstRate and Roundup had an injury rating of less than five percent. In fact, most trials experienced no injury at all.
While FirstRate is easy on soybeans, it is tough on morningglory. Although one quart of Roundup can only control two-inch morningglory, adding FirstRate can control four-inch weeds.
"When the plants get too big for Roundup alone, FirstRate will control them," Poston said.
The combination appears to handle weeds that are even larger. Hampton tries to spray a morningglory tank-mix in his Tennessee fields when the weeds are between two and six inches tall, but it is not always possible.
"I've seen the Roundup and FirstRate tank-mix control plants that have already sent out runners," he said, although he notes that is an unusual occurrence and is beyond the FirstRate label recommendations. Hampton also said the tank-mix helps alleviate time pressures because farmers can wait a little longer to spray if necessary and still get good control.
In addition, tank-mixes such as Roundup and FirstRate control weeds further into the season than Roundup alone. Even after the soybeans are mature enough to withstand morningglory competition, their vines can create problems at harvest.
Poston's research has shown that a FirstRate tank-mix controls four to six-inch morningglory better than Roundup alone. One shot of FirstRate and Roundup controlled 91 percent of morningglory 11 weeks after spraying; two applications of Roundup provided only 81 percent control at that time.
Farmers can easily incorporate a tank-mix into a Roundup Ready soybean program. Flexible timing, rates and application windows allow them to meet their individual needs. Like Hampton, many dealers believe that adding another herbicide is an economical strategy for managing morningglory.
"A FirstRate tank-mix is very cost effective," Hampton said. "It gives you the most weed control for the least amount of money."
Research shows a single application of the tank-mix can provide season-long morningglory control, saving growers the cost of a second application and the time of a second trip across the field.
"There's no comparison," Hampton concluded. "Roundup with FirstRate is hands down, two to one better than Roundup alone on morningglory."
FMC Corporation will launch a new pre-emergence soybean herbicide under the trade name Gauntlet. Gauntlet was registered by the U.S. Environmental Protection Agency late last summer.
The new herbicide combines sulfentrazone, the active ingredient in Authority herbicide, and cloransulam-methyl, the active ingredient in FirstRate herbicide manufactured by Dow Agrosciences.
"These products compliment each other very well," says Mike Steffeck, Gauntlet product manager. "Sulfentrazone provides excellent control of weeds like waterhemp, nightshade, lambsquarters and nutsedge, while cloransulam-methyl is outstanding on giant ragweed, cocklebur, and wild sunflower. Together, Gauntlet will control a wider spectrum of broadleaf weeds than any other pre-emergence soybean herbicide on the market."
"Soybean growers have always wanted a simple one-pass approach to weed control. When combined with a grass herbicide like Treflan, Pendimax or Command, Gauntlet will provide season-long control of grasses and broadleaves in one pre-emergence application. Furthermore, Gauntlet can be applied to all soybeans regardless of soil type, soil pH or corn rotation," Steffeck notes.
More information about Gauntlet will be announced later this year.