Research trials in the U.S., and more recently at the University of Saskatchewan, are proving what’s old is new again. In this case, the use of “old” herbicides such as Avadex, Fortress and Edge are making a comeback of sorts in a weed management system that’s been dubbed “herbicide layering.”
According to Clark Brenzil, who coined the term, herbicide layering is simply utilizing two to three herbicides in sequence to tackle tough-to-control weeds and to stave off weed resistance.
Indeed, herbicide tank mixtures and/or a program that utilizes a residual product in a sequential program are now the recommended practice for delayed herbicide resistance.
“It’s a good management tool for controlling some of those weeds that may not necessarily be that responsive to one herbicide,” Brenzil notes. “Wild oats and cleavers are two great examples of this.”
But even simply switching one herbicide out for another, ie. rotating herbicides, while perhaps delaying the onset of herbicide resistance, still results in selection pressure. Today, many in the industry are starting to stress the importance of using multiple modes of action and tank mixing.
“The extension message is to use multiple modes of action together in weed control programs,” says Mike Grenier, Canadian development manager with Gowan. “But it’s not only using tank mixes – it’s using products in sequence, for instance to look at the soil residual herbicides as part of this management program.”
The idea is simple: apply different modes of action within a season – layering – and rotate chemistries through the crop rotation. As it turns out, Avadex, Edge and Fortress herbicides fit very well into this strategy.
“In our scenario, you would have Group 8, Avadex or Fortress, being soil applied either in the fall or in the early spring followed with a post-emergent program during the growing season,” Grenier notes. “So in this case of Group 1 or Group 2 product use, Avadex is the pre-emergent layer providing resistance management against wild oats.”
In trials, Gowan maintains that Avadex and Fortress can provide about 90 per cent control of wild oat, while Edge (Group 3) provides 70 to 80 per cent suppression. “Then you have a post-emergent program working on a much lower level of [weed] population, so lower selection pressure. So now we have the control level approaching close to 100 per cent.”
Studies find an added bonus
Led by Christian Willenborg, weed scientists at the University of Saskatchewan (U of S) have been conducting research to determine if herbicide layering proves beneficial. “We have some good information in peas and some really good information in canola,” says Eric Johnson, U of S research assistant. “Graduate student Ian Epp’s research in canola showed some benefits, even with Roundup Ready canola, to be using clomazone pre-emergent to improve cleavers control.”
In the studies on cleavers weed control in canola, the researchers used three different modes of action – applying clomazone pre-emergent, then followed by either Clearfield, Roundup or Liberty tank mixed with quinclorac. “Even with the Roundup system, which is already pretty effective on cleavers, we found that using three different modes of action provided weed control benefits, and some yield benefits which totally surprised us,” Johnson notes. (See Fig. 1.)
The team also did studies on managing Group 2 resistant cleavers in field pea. “What we found was that if we put a pre-emergent down, that suppressed the cleavers somewhat. But then we came in and followed with a post-emergent, and we ended up with better than 80 per cent control.” (See Fig. 2.)
Going forward, the U of S is starting some work on managing Group 2-resistant wild mustard and Group 2-resistant kochia in lentil.
The big picture
Brenzil says herbicide layering has some merit for everyone. “What the U of S research has found is that if you have control taking place right at the point where the weed is germinating [with the pre-emergent], you’re going to get better yield response out of your crop, rather than waiting for the three- or four-leaf stage when there’s already been some competitive effect of that weed on that crop,” he notes.
“By having a soil active, even if it’s not doing a fantastic job of controlling the weeds, it’s suppressing the influence of those weeds on that crop, and you’re getting a bit of a yield bump by having herbicide in the soil along with your foliar product that’s coming a little later.”
An added bonus, Brenzil adds, is that by using a herbicide layering program, you’re making a pre-emptive strike against herbicide resistance. “It’s a good management tool for controlling some of those weeds that may not necessarily be that responsive to one herbicide for effective management, such as wild oats and cleavers.”
At the Herbicide Resistance Summit held March 2 in Saskatoon, Jason Norsworthy made a comment about the “treadmill” of using one weed chemistry and the very real threat of developing herbicide resistance as a result. Brenzil explains: “If you use one chemistry to death and then you allow your weed populations to get very high again, then you’re just starting from square one to select for the next Group that you’ll overuse, and so on and so on, until you paint yourself into a corner and there are no herbicide options left. At this point, the only management option left will be seeding the field to a forage crop and cut for hay until the seedbank is exhausted.”
With herbicide layering, “If you’ve got your soil active products on the ground, then you come in with your foliar and you’ve got a mix of two foliars that could still control that same weed – now you have three active in there of different families,” he adds. “You avoid that overuse and you don’t allow selection pressure to accumulate.”
This story originally appeared in the June 2016 issue of Top Crop Manager West.
An herbicide that offers multiple modes of action to help manage a variety of broadleaf weeds that can also be used in various tank-mixes to control glyphosate-resistant species will help address the challenges of weed resistance in both the current and future growing seasons.
For example, last year, a group of growers in Eastern Canada tested Armezon PRO, a new Group 15 and Group 27 herbicide. With a wide application window from early post-emergence to the eight-leaf stage in glyphosate-tolerant corn and the ability to easily tank-mix with additional products, growers were able to customize their weed management to meet their needs. When tank-mixed with atrazine in glyphosate-tolerant corn, Armezon PRO provides four modes of action.
Customizing weed management strategies is especially useful when weather prevents getting into the field for a pre-emergent application.
Managing problem weeds with multiple modes of action provides residual activity, reducing the weed seedbank and setting up fields for the next season.
Over nearly ten years, the federal department invested millions of dollars in research on this fungus and its compounds (macrocidins), which can eliminate broadleaved weeds, particularly dandelions. This breakthrough discovery has been patented in several countries and is commercially registered in the U.S. and Canada.
To assist farmers in what will likely be a more challenging spring battle with weeds, Dow AgroSciences has announced that the Diamond Rewards herbicide offer that was previously only available to Nexera customers will be open to all growers seeding any Roundup Ready and Clearfield canola varieties this spring.
Effectively immediately, with a minimum purchase of 240 acres (6 cases) of Eclipse, any Roundup Ready canola grower can qualify for the $2.00 per acre rebate. Similarly, with a minimum purchase of 240 acres (6 cases) of Salute, any Clearfield canola grower can qualify for the $2.00 per acre rebate.
Nexera canola growers will continue to receive the rebate with no minimum purchase requirement. Farmers must be registered for the Dow AgroSciences Diamond Rewards program and purchases must be made between December 1, 2016 and November 30, 2017 to qualify.
Click for more information on Eclipse and Salute.
Permit is registered for pre-emergent and post-emergent use in dry beans, and post-emergent use only in corn. Data generated by independent contract researchers has consistently shown high levels of extended residual control of volunteer canola from both pre and post-emergent applications.
For more information on Permit for volunteer canola, growers are urged to contact their local retailer.
Destra IS is a post-emergence corn herbicide with one-pass broad-spectrum knockdown and residual control, and adds two additional modes-of-action to a glyphosate tolerant system – there’s also residual control and multiple modes of action. The herbicide will allow growers to control hard-to-kill broadleaf and grassy weeds and to keep corn weed-free during the critical weed-free period.
Destra IS has a wide window of application, allowing growers to apply up to the eight-leaf stage, with excellent crop safety and a broader geography, including short season areas. It offers a smaller, easy-to-handle package and compact dry formulation, and is the only dry mesotrione formulation on the market. It offers a faster pour and bottle cleanout.
Fore more information visit Dupont.ca
DuPont Sortan IS herbicide will allow growers to control tough, yield robbing weeds, such as volunteer Roundup Ready canola, wild buckwheat, redroot pigweed (including triazine-resistant biotypes), lamb's-quarters, green foxtail, barnyard grass, and quackgrass, to keep corn weed-free to maximize yield and profits.
An additional mode of action to glyphosate, Sortan IS offers application flexibility – it can be applied pre-emergent or post-emergent, and provides extended control throughout the critical weed free period. For optimum weed control, it is recommended that Sortan IS be tank-mixed with glyphosate herbicide at 900 g ai/ha for control of additional weeds.
Sortan IS will be available at local retailers in Western Canada for the 2017 season.
For more information, visit dupont.ca
Valtera (Group 14) is a distinct mode of action that can be used as part of a fall burndown program for residual weed control where lentils will be planted the following crop season. Valtera controls a range of broadleaf weeds including pigweed, lamb’s-quarters, seedling dandelion, kochia and chickweed, and suppression of green foxtail and volunteer canola. Valtera re-activates with moisture to deliver residual control that lasts for four to six weeks in the spring. Valtera is also registered for spring or fall pre-seed burndown and residual control in chickpeas, field peas, soybeans and spring wheat. Visit nufarm.ca for more info.
CropBooster 2.0 in the herbicide tank mix produced an average yield increase of 3.3 bushels of wheat per acre in multiple field trials. In these same experiments, CropBooster 2.0 performed better than the original CropBooster with a higher yield increase.
By allowing crop plants to restart growth or to continue growing more quickly, CropBooster 2.0 is also proven to increase yields without reducing weed control.
Click here for more information.
FMC of Canada has announced a new expanded label for Authority 480 herbicide. The new label features more registered weeds and additional crops, according to a press release.
The weeds include eastern black nightshade, a particularly troublesome weed for identity preserved (IP) soybeans, and common waterhemp – the newest glyphosate-resistant weed in Eastern Canada. There are 13 weeds on the new expanded label, such as red root pigweed, lamb’s-quarters, wild buckwheat, eastern black nightshade, common waterhemp, yellow woodsorrel, common groundsel, cleavers (suppression), Powell pigweed and common purslane.
Authority offers a new group 14 weed control option for group 2 and glyphosate resistant weeds.
Several new specialty horticulture crops have also been added to the Authority herbicide label, including chickpeas, field pea, flax and sunflowers.
Command is a Group 13 pre-emergent herbicide that will provide canola growers with residual control of cleavers and will be an integral part of an overall cleaver management program in canola. It is a liquid formulation that can be tank-mixed with glyphosate for a one pass pre-seed application.
Command can be used with any canola herbicide system.
The first known report of herbicide-resistance came in 1957 when a spreading dayflower (Commelina diffusa)growing in a Hawaiian sugarcane field was found to be resistant to a synthetic auxin herbicide. One biotype of spreading dayflower was able to withstand five times the normal treatment dosage. That same year wild carrot (Daucus carota) growing on roadsides in Ontario, Canada, was found to be resistant to some of the same synthetic auxin herbicides.
Since then, 250 species of weeds have evolved resistance to 160 different herbicides that span 23 of the 26 known herbicide mechanisms of action. They are found in 86 crops in 66 countries, making herbicide resistance a truly global problem.
“Given all the media attention paid to glyphosate, you would think it would have the greatest number of resistant weed species,” says David Shaw, PhD, a Mississippi State University weed scientist. “Though there are currently 35 weed species resistant to the amino acid synthesis inhibitor glyphosate, there are four times as many weed species resistant to ALS inhibitors and three times as many resistant to PS II inhibitors.”
Scientists say what is unique about glyphosate resistance is the severity of selection pressure for resistance development. More than 90 per cent of soybean, corn, cotton and sugar beet acres in the U.S. are glyphosate tolerant and receive glyphosate treatments – often multiple times per year.
“The sheer size of the crop acreage impacted by glyphosate-resistant weeds has made glyphosate the public face for the pervasive problem of resistance,” says Shaw. “But resistance issues are far broader than a single herbicide and were around long before glyphosate-resistant, genetically engineered crops were even introduced.”
Research shows that resistant weeds can evolve whenever a single approach to weed management is used repeatedly to the exclusion of other chemical and cultural controls – making a diverse, integrated approach to weed management the first line of defense. Many growers have had great success fighting resistance by adopting a broader range of controls.
One example is found in the experiences of U.S. cotton growers in the southern U.S. After years of relying on glyphosate for weed control, resistant Palmer amaranth (Amaranthus palmeri) began to overrun crops and caused yields to plummet. Today integrated weed management programs that use a diverse range of controls have become commonplace in cotton, despite the higher cost. Growers are using cover crops, hand-weeding, tillage, weed seed removal and herbicides with different mechanisms of action in order to keep Palmer amaranth at bay.
There have been tradeoffs. Additional herbicides, labor and fuel have tripled the cost of weed control in cotton. In addition, increased tillage has raised concerns about soil erosion from water and wind. But for now, the crop has been preserved.
“Although diversification is critical to crop sustainability, it can be difficult to make a decision to spend more on integrated weed control strategies,” says Stanley Culpepper, PhD, a weed scientist at the University of Georgia. “As a result, many of the most successful diversification efforts can be found in crops like cotton where change became an imperative.”
Culpepper says that in addition to costs, another barrier to adoption of integrated weed management is the belief by some that new types of herbicides will be invented to take the place of those no longer effective on resistant weeds. But the HPPD-inhibitors discovered in the late 1980s for use in corn crops are the last new mechanism of action to make its way out of the lab and into the market.
“It would be naïve to think we are going to spray our way out of resistance problems,” Culpepper says. “Although herbicides are a critical component for large-scale weed management, it is paramount that we surround these herbicides with diverse weed control methods in order to preserve their usefulness – not sit back and wait for something better to come along.”
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Food and Beverage Ontario Annual ConferenceWed May 31, 2017
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