Change seems to be a catch word in all facets of our society today. However, in agriculture, especially in the weed control arena, change is a very tangible concept in light of critical weed resistance issues facing farmers in many of their crops.
In the past few years, farmers have reported herbicide resistance showing up in cool-season weeds like marestail, ryegrass and henbit, to name a few. Once the crop is planted, the real “bad boy” of the bunch – Palmer amaranth (pigweed) – shows up, and, in many cases, is showing signs of resistance.
As a result of this situation, farmers are changing their approach to weed control to try to delay resistance or eliminate the presence of weeds that are already resistant. Options for managing weed resistance in cotton include rotating crops or varieties, such as conventional, Roundup Ready Flex or LibertyLink/Ignite, when possible; using tillage in certain instances; developing an effective burndown program, including a residual, to fit your weed spectrum and rotating chemical modes of action.
Diversity – More Than A Buzz Word
Dr. Stephen Powles, who is an international authority on all aspects of herbicide resistance, offers an explanation of why weed resistance to certain herbicides is occurring and what tell-tale signs to look for.
“Here in the United States, the Roundup Ready crop revolution, which is fantastic technology, provided simple weed control that was adopted almost universally by farmers,” Powles says. “However, if you continue to spray one chemical for weed control with no diversity in the system, then the weeds are going to fight back in the form of resistance.
“In the initial stages of herbicide resistance, a producer will see dead weeds that show that the herbicide has worked well and live weeds of the same species beside them,” he adds. “In this instance, or even if resistant weeds have not yet appeared, having a diversified weed control program that includes an effective burndown is a necessary step to staying on top of the resistance issue.”
As an example of diversity, Powles notes that if a farmer is planting a Roundup Ready variety and knows he is going to use glyphosate postemergent, then he suggests that the farmer use an alternative burndown herbicide before planting the crop. Also, if a farmer’s burndown program includes a tankmix, then it is important to use full label rates.
Clean Fields Make Sense
Frank Carey, Valent’s field market development manager, points out that if farmers have issues with resistant marestail or ryegrass, they need to burn the field down early when the target weeds are much smaller, so that they can get good control.
“And when they do go with an early burndown,” Carey says, “farmers need to use a residual product, such as Valor herbicide, to keep the field clean. If we also have to fight pigweed, having a clean field allows for better soil contact for the residuals that are being applied at planting for pigweed control.
“Plus, with a good burndown, the ground warms up quicker, and the crop emerges more evenly because there is no weed competition,” he adds.
New Chemistries Play A Role
Rotating chemical modes of action is also important in managing weed resistance in cotton. A new chemistry that BASF launched in 2009 is Kixor herbicide technology that is found in Sharpen herbicide in cotton. According to BASF, Kixor is a “potent inhibitor of chlorophyll biosynthesis” that ultimately leads to “rapid weed death.”
Gary Fellows, BASF’s tech service regional manager, says Sharpen works well in a glyphosate tankmix at burndown because Sharpen can control the broadleaf weeds, even the glyphosate-resistant ones like marestail, and the glyphosate can control the grasses. He says together the two herbicides appear to have a synergistic effect.
“There are other herbicides available in this chemical class, but Sharpen is a little more aggressive as far as speed of control,” Fellows says. “It’s ‘somewhat systemic’ in that you will see foliar movement within the leaf, but it’s not systemic like glyphosate, dicamba or a phenoxy that moves down into the root system. This herbicide has good activity on glyphosate-resistant Palmer pigweed and marestail.”
Fellows also notes that Sharpen herbicide has a 45-day pre-plant interval to avoid any potential crop response with the cotton.
Burndown And Beyond
Mississippi State University Extension cotton specialist Darrin Dodds says many of the state’s cotton producers target marestail and/or ryegrass – whether they are herbicide resistant or not – at burndown.
“From a cotton standpoint, ryegrass is more of an issue with stand establishment,” Dodds says. “It’s hard to get good seed-to-soil contact when the planter has to run over a big clump of ryegrass. It’s important to make herbicide applications far enough ahead of planting to get adequate control and allow the vegetation to decompose.
“We are beginning to look at some of the graminicides, such as Select Max for Italian ryegrass control,” he adds. “If you put Select Max out when it is cold, ryegrass may sit there for two to four weeks and appear unharmed. Then very slowly you’ll see the grass begin to die back. You have to give the herbicide time to work. We’re also seeing some Gramoxone Inteon go out.”
Dodds adds that if you need to include a plan for pigweed control past your burndown application, he recommends using a product, such as Reflex, 14 days ahead of planting.
“In a perfect world, this may carry you through your first over-the-top application of Roundup and Dual Magnum or Roundup and Warrant.”
Another weed control issue that Dodds brings up is that some producers are seeing erratic control from 2,4-D on marestail.
“We’re seeing more applications of a combination of 2,4-D and dicamba,” he says. “If you don’t completely kill the weeds in your burndown application, applying Gramoxone Inteon and Cotoran behind the planter may be an option for you.
“It will clean up remaining vegetation (within reason), plus it will lay down a residual, which can help with pigweed later,” Dodds adds.
Cooperation Within The Industry
Obviously, it’s an understatement to say weed control programs in cotton are more management intensive today than they were in what Stephen Powles referred to as “the Roundup Ready crop revolution” era. However, the good news is that the entire cotton industry is working together to come up with multiple options and incentives to help farmers build effective weed management programs, often on a field-to-field basis.
One example of competitor cooperation is the 2011 Cotton Performance Plus Program, which offers farmers up to $20 per acre in refunds on several residual herbicides.
Qualifying states include Alabama, Arkansas, Florida, Georgia, Kentucky, Louisiana, Maryland, Mississippi, Missouri, North and South Carolina, Tennessee and Virginia. For more information, visit genuity.com/performanceplus.
Right now it’s February, and symbolically speaking, it’s almost kickoff time in the 2011 cotton-growing game. Just remember to keep in mind that the first step to a winning season is an effective burndown that fits your unique situation.
Contact Carroll Smith at (901) 767-4020 or firstname.lastname@example.org.