Sally Behringer, Content Editor
Debra L. Ferguson, Managing Editor
Owen Taylor, Editorial Director
Welcome to AgFax Weed Solutions - South, sponsored by Nufarm.
Time Your Herbicide Applications for Maximum Control
The time of day when you spray Palmer amaranth greatly influences the efficacy of the herbicide treatment. That's the finding from a concentrated, multi-state research study. Researchers from the University of Georgia, North Carolina State University, Louisiana State University, Mississippi State University and the University of Tennessee worked together to produce the study.
Liberty herbicide sprays
were more effective when application was delayed until at least 2 hours
Results suggest the time of
day effect may be partly due to reduced translocation of the herbicide
when applied at night or at sunrise.
The time of day of application affected Liberty herbicide efficacy the most. One study recommends that Liberty should be applied in the Southeast and Midsouth from two hours after sunrise through one hour before sunset for most optimal control of Palmer amaranth.
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Stanley Culpepper, Professor and Extension Agronomist, University of Georgia was a key driving force in completing the large, multi-state study. And while the researchers are learning more about how herbicides react to applications at different times of the day, they have a lot more to learn about “why.”
“I had a lot of complaints (about Liberty) that I could not figure out,” he says. “One day we were literally spraying (Liberty) at the crack of dawn, and it didn’t work. I went back to the complaints and it was always when it was applied very early in the day. I started connecting the dots. I don’t know that we have the answers yet – could it be translocation? It’s not clear.”
The goal, according to Culpepper, is helping growers optimize product efficacy and get the best return on investment from their herbicides.
“You really want to figure it out so you can help your growers – that’s what it’s all about,” Culpepper says. “It’s all about maximizing control. Keep in mind that, in Georgia, our cotton industry alone has spent over $1 billion in controlling glyphosate-resistant Palmer amaranth since its first discovery.
"We need to maximize every single approach every time we do it. It’s the difference between somebody making money and not making money on a field. I have to spend my time maximizing every aspect of their weed management system. That’s why we‘re looking at time of application, to make that as effective as possible.” Click here to see more info.
Click Table to Enlarge.
Time of Day to Spray Pigweed?, Nochaway Ag Update, University of Georgia Extension
To see more data from the studies and download the abstracts, click here.
Palmer Amaranth: The Scourge of the South
Battling glyphosate resistant Palmer Amaranth has become a major focus of crop producers across the South, especially in cotton and soybeans.
Alan York, Professor Emeritus at North Carolina State University, is one of the leading researchers exploring ways to control glyphosate resistant Palmer Amaranth more effectively, and he says it’s a challenging job. We asked him about the weed and what makes it so tough to control.
“It has a number of characteristics about it,” he explains. “Over all you can say it’s a very vigorous growing plant – a very tough, competitive plant.
"There’s physiology inside the plant that helps it deal with drought conditions. Bottom line, it can be bone dry and the crop wilting and Palmer amaranth is happy. It grows fast. When it initially starts it’s not that fast but once it gets to 4 to 6 inches, it’ll easily grow one inch a day and under good conditions it’ll grow two inches a day. Also, it produces a lot of seeds. We’ve actually documented plants in North Carolina last year with 1.5 million seeds per plant.”
So what recommendations does York have for controlling Palmer amaranth successfully? Here are some pointers:
1- Apply at least one residual herbicide either prior to or right behind the planter.
2- Use more than one active
ingredient to get better weed control pre-emergence.
3- In conventional tillage
cotton, York recommends starting with a soil-incorporated herbicide.
4- For the conservation tillage
grower he strongly recommends a residual herbicide in the early burndown
3 or 4 weeks ahead of planting followed by a pre-emergent herbicide.
5- Add a residual herbicide to post-emergence sprays.
6- Consider a layby directed spray. “I think there’s a lot of value to a layby directed spray,” he says. “I know they’re a pain to put out but they really work and I really recommend them.”
1- York is seeing a trend in
full-season (i.e., not double-cropped) soybeans where growers are
applying a residual herbicide ahead of planting.
2- Again, using more than one active ingredient will give more complete control of weeds and help control resistant weeds more effectively.
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Georgia's Culpepper offers some timely tips and recommendations on Palmer amaranth control as well.
“It’s unfortunate that (commodity) prices are low, but you still have to control the Palmer amaranth,” he emphasizes. “You can’t cut corners with this weed. We have to be and remain aggressive. It’s not a one season battle. If you cut corners one year, all of the hard work we’ve done the last five years is down the drain.”
The most important recommendation from Culpepper is timeliness: “The timeliness of the sprays is critical,” he says. “The challenge is dealing with all of the curveballs that you get, like getting 8 inches of rain. Growers know what to do but getting the weed control out there in a timely fashion can be hard. But it’s critical.”
To see the entire interview with Alan York, click here. To download a recent study on Palmer amaranth control by York and Wesley Everman, a weed science Extension specialist at North Carolina State University, click here.
A New Definition of “Superweed”
The term "Superweed" is bandied about in a lot of headlines -- over used and often incorrectly applied. The continued confusion prompted the Weed Science Society of America (WSSA), in league with 6 other scientific organizations, to recommend a new definition for the term.
Why is this necessary? Because many normally respected sources have it wrong. For instance, The Oxford Dictionary defines superweeds as “a weed which is extremely resistant to herbicides, especially one created by the transfer of genes from genetically modified crops into wild plants.” Wrong.
And that is just one example, according to WSSA, of why a new definition is needed.
There’s no evidence that gene transfer from genetically modified crops to weeds is a major factor in the development of herbicide resistance issues faced by farmers ,” says Lee Van Wychen, Ph.D., and WSSA science policy director. “What’s causing herbicide resistance to develop in weed populations is the overreliance on herbicides with a single mechanism of action to control certain weeds. That leads to the selection of weeds resistant to that mechanism of action.”
The new definition of “superweed” proposed by WSSA is:
“Superweed: slang used to describe
a weed that has evolved characteristics that make it more difficult to manage,
due to the repeated use of the same management tactics. Over-dependence on a
single tactic as opposed to using diverse approaches can lead to such
According to the WSSA, the most common use of the slang “refers to a weed that has become resistant to one or more herbicide mechanisms of action due to their repeated use, in the absence of more diverse control measures. Dependence on a single mechanical, biological or cultural management tactic has led to similar adaptations.”
For more information about
superweeds and to download the new WSSA fact sheet on superweeds,
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Wild Spring Weather Leaves Growers
Needing Herbicide Options
Thanks to some wild weather, it’s been a wet, crazy spring. In some areas soybeans remain unplanted, pre-emergent herbicides may have broken, gotten too much or not enough moisture or just plain didn’t get put on the acre. Planting in key crops like cotton is far behind in parts of the Cotton Belt. You might find yourself in a wide variety of different scenarios right now. But you have herbicide options.
Especially in areas where there are glyphosate resistant weeds, a dual mode herbicide such as Cheetah Max (glufosinate and fomesafen) is the reliable way to control a wide variety of weeds. It can be applied in a variety of situations, such as:
Pre-plant burndown or preemergence on any conventional or transgenic variety of cotton or soybeans (see label for restrictions on planting cotton);
Postemergence for over-the-top use in LibertyLink soybeans; and
Post-directed applications with hooded spray equipment in any cotton variety.
Note: Cheetah Max should never be applied postemergence over the top to any type of cotton.
Cheetah Max is a unique combination of 2.0 lb glufosinate ammonium and 1 pound of fomesafen/gallon. This provides excellent burndown plus residual weed control, with two different modes of action.
NuFarm herbicide recommendations by region: Click here.
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