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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.
The winter wheat crop continues to grow well. The cool temperatures have slowed growth a little. The frost on the mornings of May 8 and 9 appear to have had little impact on the crop other than some minor damage to leaf tips. Fortunately, the wheat was not in head. Some fields in the Niagara and Haldimand regions still require a nitrogen application but will have to wait until the fields are fit. A number of fields with split applications of nitrogen still require the second application as well. Red clover under seeded in the wheat is doing well as there has been adequate moisture for germination and early growth. At this point in time there is marginal benefit to applying herbicides to the wheat crop. Winter annuals have already impacted the crop and most perennial weeds (sow thistle) are not fully emerged. Late planted fields that are thinner may still benefit from a herbicide application.
Septoria leaf spot and powdery mildew continue to be the most common diseases present in the lower canopy. Wheat streak mosaic virus was confirmed in Huron County. With the rapid growth of the crop and favourable weather conditions, it is important to continue scouting to determine if fungal disease infection is progressing up the plant (especially on susceptible varieties) and is critical to determine if a fungicide application is needed and at what timing (flag leaf/T2 or flowering/T3).
Stripe rust was also found in one field in Oxford County as well as another in Stoney Point (Essex County). As mentioned last week, there are large differences in variety susceptibility to stripe rust and fields planted with susceptible varieties should be scouted and targeted first. Trace amounts of stripe rust was detected when the field was sprayed on May 3, 2017. In a week, the disease went from less than 1 per cent to 100 per cent incidence and 30-60 per cent severity where a fungicide was not applied. Fields planted to tolerant or resistant varieties need to be regularly assessed from now until heading to assess stripe rust risk. Remember strobilurin based fungicides should not be applied on wheat from the boot stage and later.
Spring cereal acreage will likely be lower this year as it has been difficult to get the crop planted. If it is still desired to plant a spring cereal for feed a good option would be oats or adding peas to the oat crop to increase crude protein. Spring cereals that are planted have sprouted but not yet emerged.
The number of corn acres in the ground has changed very little in the last week as significant rainfall occurred across the province May 4 to 6. Much of the province received about 50mm (2 inches) with some areas receiving more and others less than that. In most areas the fields are draining well. Fields with less than adequate drainage or fields with poor crop rotations and lots of tillage are draining more slowly. A few days after the rain fertilizer spreaders, sprayers and some planters were getting back on the sandier soils. As planting is further delayed the temptation will be to plant in less than ideal conditions. Keep in mind what happened last year when corn was planted wet and the rain stopped. Roots couldn’t penetrate the side wall compaction and the slot opened up exposing the seed. The ideal corn planting depth is 1.5” to 2” (3.5 to 5 cm).
Chickweed and other prostrate plants are attractive for egg laying by black cutworm moths arriving on winds blowing up from the US. Trapping networks in the U.S. and Ontario are reporting a higher and earlier than normal black cutworm flight this spring. Preventative measures include delaying planting by two to three weeks after a burn down which causes the young cutworm larvae to starve, prior to the crop emerging. Prolonged wet weather like this year, reduces the chance for these preventative measures to be put in place. Take note of those fields planted shortly after burn down and plan to scout for leaf feeding and cutting injury every three to four days, once the crop emerges until it is safely past the V4 stage.
Armyworm moths are being caught in traps earlier and more abundant this year. Scouting cereals, mixed forages and emerging corn fields will need to take priority in the last two weeks of May.
A small percentage of the canola crop has been planted due to wet field conditions. Early planting of the crop is recommended to avoid Swede Midge infestations. Early planting may be a challenge this year. Ideally the crop should be planted by May 20th. Crop insurance planting deadlines range from May 31 to June 10 depending on location.
Forage and Pasture
Hay and pasture growth has been good due to adequate moisture conditions. Excess moisture has made it difficult to get livestock on the pastures and some are pulling livestock off as it is no longer fit.
Based on this re-evaluation, Health Canada will continue the registration of products that contain glyphosate, but will require updates to product labels. By April 2019, manufacturers will be required to ensure that all commercial labels on pesticides containing glyphosate include the following:
· A statement indicating that re-entry into the sprayed areas should be restricted to 12 hours after application in agricultural areas where glyphosate products were used.
· A statement indicating that the product is to be applied only when the potential to spread to areas of human activity, such as houses, cottages, schools and recreational areas, is minimal.
· Instructions for spray buffer zones to protect non-targeted areas and aquatic habitats from unintended exposure.
· Precautionary statements to reduce the potential for runoff of glyphosate into aquatic areas.
Health Canada will continue monitoring research on potential impacts of glyphosate products to ensure the safety and security of Canadians and the environment. The department also says they are committed to working closely with its international counterparts on evidence-based approaches to pesticide regulations.
Don't forget, the Pesticide Label Search App can help you find the latest detailed instructions, first aid statements and warnings on the label.
1. Pre-seed or pre-emergent burndown: both ensure the crop is off to a clean start. An effective strategy is tank-mixing glyphosate with a pre-seed or pre-emergent burndown of a Group 14 herbicide to provide early season weed control and can target weeds that cannot be controlled in-crop. Using multiple modes of action can also delay glyphosate resistance and manage existing Group 2- and glyphosate-resistant weeds.
2. In-season herbicide application: this manages weeds that may have emerged later.
3. Pre-harvest application: improves crop uniformity, harvestability and perennial weed control.
Research by University of Guelph weed scientist Dr. Clarence Swanton shows that soybean plants can sense the presence of weeds in the soil, and will change their physiology and growth patterns if they detect above-ground weed competition.
Swanton and his team are conducting ongoing research to determine whether these cellular-level changes impact yield, or if the plant can repair itself or compensate for any injury.
In earlier research, Swanton’s team also determined that the critical weed- free period for soybeans is from the first to the third-trifoliate leaf stage, and weeds that emerge with or after the soybean crop have an impact on yield.
Bryce Geisel, technical marketing specialist for herbicides at BASF Canada, says it’s important to choose products that use a different mode of action than the burndown. “This can control a wider spectrum of weeds and help delay herbicide resistance,” he says. “Doing a pre-seed application can help growers properly time an in-crop application, and ensures that weeds are more manageable for that second pass.”
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.
About a year ago, a group of researchers discovered Palmer is resistant to the herbicide class known as PPO-inhibitors, due to a mutation —known as the glycine 210 deletion — on the PPX2 gene.
“We were using a quick test that we originally developed for waterhemp to determine PPO-resistance based on that mutation. A lot of times, the test worked. But people were bringing in samples that they were fairly confident were resistant, and the mutation wasn’t showing up. We started to suspect there was another mechanism out there,” says University of Illinois molecular weed scientist Patrick Tranel.
Tranel and his colleagues decided to sequence the PPX2 gene in plants from Tennessee and Arkansas to see if they could find additional mutations. Sure enough, they found not one, but two, located on the R98 region of the gene.
“Almost all of the PPO-resistant plants we tested had either the glycine 210 deletion or one of the two new R98 mutations. None of the mutations were found in the sensitive plants we tested,” Tranel says.
Furthermore, some of the resistant plants had both the glycine 210 deletion and one of the new R98 mutations. Tranel says it is too early to say what that could mean for those plants. In fact, there is a lot left to learn about this resistance mechanism.
“We don’t know what level of resistance the new mutations confer relative to glycine 210,” Tranel says. “There are a lot of different PPO-inhibiting herbicides. Glycine 210 causes resistance to all of them, but we don’t know yet if the R98 mutations do.”
The team is now growing plants to use in follow-up experiments. Tranel hopes they will be able to determine how common the three mutations are in any given population. “That way,” he says, “when a farmer sends us a resistant plant and it doesn’t come back with the glycine 210 deletion, we will be able to tell him how likely it is that he’s dealing with another one of these mutations.”
In the meantime, other research groups or plant testing facilities could use the new genetic assay to detect the mutations in Palmer samples. Tranel hopes they will. “The more labs testing for this, the more we learn about how widespread the mutation is,” he says.
The article, “Two new PPX2 mutations associated with resistance to PPO-inhibiting herbicides in Amaranthus palmeri,” is published in Pest Management Science. The work was supported by a grant from the USDA’s National Institute of Food and Agriculture.
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
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SeedMaster Crop TourWed Jul 26, 2017
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