With a new planting season near, talk of glyphosate-resistant weeds is again on growers' minds. Two Nebraska families feel they've solved the problem before it hits their farms.
They now grow LibertyLink corn on most of their corn acres, both to prevent resistance problems and to ward off troublesome weeds that glyphosate could not always handle.
“We first used LibertyLink corn in 2004 to cleanup shattercane,” says David Rasmussen, who farms with his brother, Dan, and father, Larry, in Albion, NE. “We planted more of it in 2005 and will have more in 2006.”
Other Albion growers, Bryce Naber and his father, Loren, are now planting at least 75% LibertyLink corn. “We've received good control on almost all weeds,” says Bryce. “We still have some problems with sandburs, but everything is weak on sandburs.”
LibertyLink transgenic corn has been around since the late 1990s. The corn is resistant to Liberty herbicide (glufosinate) from Bayer CropScience. The post-emergence over-the-top applied herbicide is successful against most weeds.
Like Roundup Ready (glyphosate) corn from Monsanto, LibertyLink is designed to ease the weed control burden for growers. Both the Nabers and Rasmussens have worked LibertyLink corn in their rotation with Roundup Ready soybeans. Their aim is to control velvet leaf, waterhemp, cocklebur, sunflower, sandbur, foxtail, shattercane, butterweed and other regional weeds. They are also trying to prevent herbicide resistance.
“The potential for waterhemp or marestail resistance (that has been seen in some growing regions) is 90% of the reason we decided to use some LibertyLink corn,” says Bryce Naber, whose rotation is about 50% corn and 50% soybeans
“Roundup works really well on our corn and beans. I like the luxury of being able to use Roundup to clean up our soybean fields. But as in the past, when chemicals have worked well for a while then not, we want to use other means of weed control to hopefully prevent resistance from happening.”
The Nabers have also used conventional corn varieties and have had good success with a herbicide combination of Steadfast from DuPont and Callisto from Syngenta. “We'll probably grow less conventional corn for now because of the success we've had with LibertyLink,” says Bryce.
The Rasmussens have a one-third soybeans, two-thirds corn rotation, along with some alfalfa. “When we went with our first LibertyLink corn, we found that it was safe for the crop and did a pretty good job on the shattercane,” says Dan Rasmussen. “It also did a good job of controlling buttonweed. But we had some problems with foxtail.”
The application rate for Liberty herbicide is 32-34 oz./acre. Cost is about $25/acre. The Rasmussens and Nabers apply it via ground rigs. A pre-emergence application of Basis from DuPont was used by both families.
Bob Hartzler, Iowa State University Extension weed specialist, says LibertyLink corn is a good product and a good alternative to conventional corn and Roundup Ready corn. “It's an excellent herbicide, but overall it's not as good a Roundup and its biggest downfall is that everyone compares it to Roundup,” he says.
However, for growers concerned about resistance, Hartzler says LibertyLink should be considered. “It's primarily a contact herbicide, meaning timing of application is important,” he says. “Where most people have had problems is when they let weeds get too big.
“The best time to apply is when weeds are 2-4 in. in height, so a one-pass program is likely not going to work consistently. It probably needs to be used in conjunction with other strategies.”
A pre-emergence application to knock down the most troublesome weeds can often allow growers to delay the Liberty application time to a maximum corn plant height of about 24 in. In that situation, Liberty should likely hold down weeds until the crop canopy fills in to prevent further weed growth, says Hartzler.
He notes that early on Liberty was labeled at a lower rate and did not perform up to some grower expectations. “But with the higher application rate (32-34 oz./acre) it should perform more consistently,” he says.
LibertyLink corn is also popular because it includes the Bt gene with resistance to Herculex insecticide from Pioneer Hi-Bred.
“We also like LibertyLink because we can use the Herculex insecticide technology,” says David Rasmussen. “That seems to be a good combination for us.”
He points out that in some instances, excessive tank foaming was a problem with Liberty. They hoped to solve the problem with a better adjuvant mixture.
“With Liberty, we haven't seen any injury to the crop and we really like how it can clean up volunteer corn or soybeans,” he says.
Hartzler says that despite concerns over glyphosate resistance, expect to see more Roundup Ready corn this year and beyond.
“Roundup Ready corn has really taken off,” he says. “I'm sure it will not reach the saturation that has been reached with soybeans, but I wouldn't be surprised if it's 50% (of corn acres) by 2007. It is already 80% in parts of the western Corn Belt.”
He says most farmers look at the short-term situation and realize the strength of glyphosate.
“The convenience of using one product on both crops greatly simplifies things,” he says. “Until resistance becomes a main issue, we likely will continue to see an increase in Roundup Ready corn acres.”