University weed scientists and Extension farm agents across the Cotton Belt are making a concerted effort to help growers understand the threat of herbicide resistant weeds and to help them make good management decisions that will extend the life of new technology and improve crop profitability.

There has been much written about the use of glufosinate, arguably the next best thing to glyphosate because of glyphosate resistance problems with Palmer pigweed and other weeds.

Though the most ‘in-the-news’, glyphosate is not the only herbicide with resistance issues. Several families of herbicides share the plight of glyphosate.

New chemistries, whether herbicides, fungicides or insecticides, all strive to delay or prevent seemingly inevitable resistance problems associated with over-use or miss-use.

The LibertyLink system is one of these technologies.

FiberMax and Stoneville LibertyLink cottonseed varieties, LibertyLink soybean varieties, multiple corn brands and InVigor LibertyLink canola contain the LibertyLink trait, which confers full tolerance to Liberty herbicide, or glufosinate.

Long-time North Carolina Weed Scientist Alan York says bluntly that there are no more silver bullets for weed control, especially for control of Palmer amaranth.

Glufosinate is the best next herbicide growers have, and they need to use it wisely to prevent a similar scenario that we now see with glyphosate resistant weeds, York says.

For several years a number of cotton growers in the Upper Southeast have used glufosinate on Phytogen brand cotton that contains a Widestrike gene and a marker gene similar to the resistant gene used in LibertyLink cotton varieties.

Phytogen Widestrike varieties do not have the LibertyLink trait, which is what confers tolerance to full labeled rates of glufosinate.

In some cases, best management practices are compromised in order to avoid injury to the crop.

When growers use glufosinate on Phytogen Widestrike cotton, they have to pay special attention to timing of application — even down to what time of the day it is sprayed on cotton plants.

They also risk damage to the cotton crop, and they often reduce the rate to reduce the risk of damaging their crop.

May hasten resistance

However, management practices that reduce the herbicide’s efficacy to control weeds, including glyohosate resistant Palmer pigweed, may potentially hasten the development of resistance. 

“FiberMax and Stoneville LibertyLink varieties are bred with tolerance to full labeled rates of Liberty herbicide to increase weed control, help avoid escapes and steward the LibertyLink technology,” says Steve  Nichols, U.S. agronomic manager for seed and technology for Bayer CropScience, the company that markets the LibertyLink trait.

 “It is crucial that growers follow best management practices to preserve the long-term viability of Liberty herbicide as a sustainable tool for effective weed control,” Nichols says.

In cotton, Bayer offers several FiberMax and Stoneville cottonseed varieties containing LibertyLink technology.

“We encourage growers to always read and follow label recommendations and use best management practices,” Nichols says.

“With Liberty herbicide, that includes practices such as making applications at proper timings based on weed size, following suggested labeled rates, using optimum spray volumes, use of tank-mix partners when warranted, and the use of residual herbicides for a complete weed control program. 

“Growers who plant FiberMax and Stoneville varieties with the LibertyLink trait and use labeled rates of Liberty herbicide along with best management practices for weed control can enhance the effectiveness of their weed control program and help minimize the risk of resistance development,” Nichols explains.

“In the long-run, the grower can be successful in effectively controlling weeds and producing a profitable cotton crop,” he adds.

“If growers use LibertyLink trait technology and Liberty herbicide in the way it was developed to be used, they can go in at the right time and spray when the weed size indicates it’s time to spray — they don’t have to wait for their crop to get to a certain size to spray.

“If the weeds get away a little bit and they need to apply Dual or other tank-mixes, they can do that without any fear of damaging their cotton crop.

“If you are managing to avoid injuring your crop, you are not likely doing the best job you could be doing of controlling weeds and maintaining clean fields.

“With LibertyLink technology, which offers full tolerance to Liberty herbicide, growers can better manage their crop and more effectively control weeds,” Nichols says.

He explains that LibertyLink trait technology is going to be included in many future cotton varieties for years to come.

Want to keep it around

“We want to have this technology around for growers for a long time, and it’s absolutely critical that the technology be used wisely.

“Incorporating LibertyLink technology as a component of a total weed control program and following Liberty herbicide label directions will help ensure that will happen,” he adds.

Growers saw all too well what happened when they over-used Roundup Ready technology. It was and is a great product, but it has created a whole new set of management problems with resistance. Over-use and miss-use of glyphosate resistant technologies has resulted in some unmanageable situations, especially with pigweed.

In past years in the Upper Southeast, the knock on planting LibertyLink cotton varieties has been perceived lower yields. The varieties that contained the LibertyLink trait simply didn’t yield quite as well in University variety testing programs as other varieties.

Though Nichols agrees that was the case to some extent in some university variety trials with the first released LibertyLink varieties, he contends many growers achieved high yields with very good fiber quality on their farms and were able to control weeds without hand weeding, which translates to a cost savings.

Nichols says two new Liberty Link varieties with high yield potential, ST 5445LLB2 and FM 1944GLB2, will be available for the 2012 season.

With ST 5445LLB2, Liberty herbicide can be applied at full labeled rates to manage weeds with no risk of injury to the crop.

In the case of FM 1944GLB2, growers have the flexibility to apply glyphosate herbicide or Liberty herbicide to best manage weeds on their farm. 

This GlyTol LibertyLink herbicide stack combination offers growers additional options in their weed control program.

Nichols says these new varieties will be available to growers in the Upper South, Southeast and Mid-South this year.

In addition to these new varieties, ST 4145LLB2 was released in 2011, and will be available to growers in greater quantities in 2012.

“Stoneville ST 4145LLB2 was released on a limited basis last year, but will be available in excellent supply in 2012,” Nichols says.

“More than 300 growers had the opportunity to evaluate the new variety in 2011. Now, those farmers are making variety decisions, and we are already seeing many of those growers increasing their acreage planted to this variety for 2012.”

“We know how much it costs to produce a crop of cotton, and we understand that growers are mindful of managing their input costs to remain profitable. Following best management practices may cost a little more up front, but in the long-run, best management practices and wise use of any new technology or product is typically going to pay off for growers,” Nichols says.

rroberson@farmpress.com