DELHI, La. -- In 2005, Louisiana producers planted approximately 615,000 acres of cotton. “We’re like many cotton-growing states in that the vast majority of acreage is in transgenic varieties to help with both weed and pest problems,” said Donnie Miller, research weed scientist at the LSU AgCenter Northeast Research Station. “When speaking of help with weed control, most cotton varieties planted are Roundup Ready.”
To show the dramatic impact Roundup Ready technology has had, Miller, speaking at the Louisiana Cotton Forum, pointed to state herbicide use just seven or eight years ago. At that time, “with glyphosate, we were applying about 75,000 pounds of active ingredient. With Staple, we were applying about 8,000 pounds; Cotoran was about 325,000 pounds; MSMA was at 475,000 pounds; diuron was just over 100,000.”
Turning the clock forward to 2003, there was a dramatic change in response to Roundup Ready technology. At that time, Louisiana “saw a 715 percent increase in glyphosate use. Staple use decreased 80 percent, Cotoran was down 85 percent, and MSMA was down 64 percent. We did see an increase of 134 percent with diuron — the only herbicide besides glyphosate we saw an increase on. I think producers began to see glyphosate/Diurex (diuron) was a good combination at lay-by to provide knock-down weed control. That combination also provides a residual control at lay-by.”
Across the United States, the same trends have been seen with glyphosate usage jumping 753 percent from 1997 to 2003. Meanwhile, many of the at-planting materials are on the decrease.
The benefits from Roundup Ready systems are many. Miller pointed to a few:
• Potential to eliminate chemical applications and reduce tillage operations.
Producers quickly learned that as long as timely, over-the-top applications occurred on small, actively-growing weeds, they could reduce or eliminate pre-emerge materials normally applied at planting. “That reduced overall costs. And tillage could be reduced or eliminated entirely as long as timely applications occur.”
• Easy to understand “application trigger.”
When weeds reach 1 inch to 3 inches, “go ahead and spray whether they’re grasses or broadleaves.”
• Broad spectrum of control.
Gone are the days when producers had to tank-mix two herbicides to control both grasses and broadleaves. Now, both can be managed with a single herbicide application.
• Allows for a “systems” approach.
“Some people treat Roundup Ready cotton with only glyphosate. Others treat Roundup Ready with glyphosate until the four-leaf over-the-top restriction. Then, they treat it like regular cotton, utilizing conventional herbicide programs. Still others work a combination of the first two systems — they use glyphosate and incorporate some of the standard materials available.”
• Rotational flexibility.
Glyphosate use provides no residual, long-lasting effect and allows the rotation of crops year-in and year-out. Producers aren’t locked into specific crops.
On the flipside are some problems with the Roundup Ready system.
• Proper application timing.
“The four-leaf application restriction over-the-top isn’t (all that popular). I think most would prefer to make at least two applications over-the-top to feel they’re getting their money’s worth from the system. But at a time of the year when we have high heat and good moisture conditions, it’s very hard to get those two applications done prior to the four-leaf restriction, especially over larger acreage.”
• Rates on perennials.
“With the 0.75-pound to 1-pound active rate most put out, good activity is observed on most annual weeds. But with perennials, rates need to be much higher. And the question is: are you really controlling those or just keeping them beat back until the crop is out?”
• Crop tolerance.
“You go much past the four-leaf restriction with an over-the-top application and you can delay maturity and push fruit a couple sites higher up the plant. That can affect yields if the plant can’t compensate later in the season.”
• Reduced herbicide development.
This is one of the biggest concerns associated with Roundup Ready technology, said Miller. “Many companies are no longer putting money, time or effort into development of new chemicals. They don’t think they’ll see a return on their investment. That’s been a definite impact from this technology.”
In the coming year, Roundup Ready Flex cotton will be introduced. This will allow over-the-top applications further into the crop’s growth.
“Total in-season use annually will be 5.3 quarts of glyphosate in the crop. Total over-the-top applications can reach a gallon of glyphosate (128 ounces) from planting to 60 percent open boll. For single applications, an aerial application can use 22 ounces and a ground application can use 32 ounces.
“From 60 percent open boll to preharvest, Flex cotton is allowed 44 ounces of glyphosate per acre. There is also a maximum 44 ounces between lay-by and 60 percent open boll. That’s a lot of glyphosate.”
The new cotton provides tolerance beyond current restrictions. Producers will no longer need to go under the plants to avoid maturity delays and yield problems. Specialized equipment intended to reduce herbicide/plant contact can be done away with in Flex cotton.
Miller cautions that because producers can go over-the-top past the four-leaf stage, there will be a temptation to delay the initial glyphosate application. Producers might want to wait until “there are enough weeds out there to justify an application.” Such an approach is dangerous, said Miller, and is perhaps “the biggest detriment to this new technology. Too many forget the serious early-season weed competition that can occur and be hidden by the ability of glyphosate programs to clean up a weedy field…
“I’m very concerned that producers will delay that initial application. Not only will the weeds compete with the crops, but everything the weeds host — pests and disease — could bother the cotton too.”
Use of the new weed control system hinges on several factors, said Miller.
• How well can a producer cover his acres and make timely applications?
“That’s where (producers) are the experts. It’s very easy for me to make a timely application on a (small) research plot. There’s a big difference, when you’re talking about covering 500 or more acres.
“If you feel confident that, after a rain, you can get back in the field within a couple of days to make an application and limit weed size and competition, application of residual materials may be unnecessary.
“Inclusion of materials with residual activity in a Roundup Flex system may buy producers time in making the glyphosate application and limit the competition that can occur when application is delayed and weeds become larger. In addition, inclusion of other materials can increase the activity of glyphosate on weeds less sensitive, such as hemp sesbania and pitted morningglory, especially when these weeds are larger. The main benefit from including other herbicides in a Roundup Ready Flex system (either at planting or in co-application over-the-top) is to introduce other modes of action into the system as a means of preventing weed resistance associated with continuous use of glyphosate.
“I think most producers would agree to the positive impact of this technology and anything we can do to assure its longevity will be beneficial.”
• Technology costs.
The old Roundup Ready system and Flex “both work. Both are effective and we’re already growing the cleanest cotton crops ever. With the increase in the tech fee associated with the Flex varieties, it’ll be up to each producer to decide if that extra money is worth it.
“Producers may feel the potential to reduce cost/time associated with applications over-the-top throughout the growing season with larger, faster-moving equipment and the ability to reduce the number of application trips through the field by co-applying insecticides and plant growth regulators with glyphosate in over-the-top applications more than offset the increase in tech fees.”
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