Four Reasons To Consider Soil-Applied Herbicides This Fall – for Sep. 6, 2010

Soil-incorporated herbicides like Edge and Avadex used to be an important weed control option on many farms. The adoption of zero till means many farmers no longer use soil-incorporated herbicides, but some of these herbicides can now be used without incorporation on lands under a zero-tillage management system, so they still have a fit. Here are four reasons why these products should be considered — especially this fall.


Brian Wintonyk, western crops agronomy lead with Dow AgroSciences, says Edge provides a fall application option for farmers looking to control a broad spectrum of broadleaf and grassy weeds in next years canola, pea, yellow mustard, beans, lentil, soybean and sunflower fields. “Edge provides growers with cropping flexibility.”

“There is a significant reliance by growers on Group 1 and 2 herbicides and since Edge is a Group 3 product it provides a great herbicide rotation option. As a Group 3 product, Edge not only reduces the risk of the development of herbicide resistance, it also controls a number of problem weeds which have already developed resistance to chemistries, such as Group 2 resistant kochia,” says Wintonyk.

Avadex, another fall-applied granular herbicide, is a Group 8 herbicide and will kill Group 1-and Group 2-resistant wild oats, as well.


Yield robbing wild oats are still the number one weed problem most farmers face. Tim Kunkel, Avadex product manager, Gowan Company, says, “When you control wild oats with Avadex there is no wild oat competition for moisture or crop nutrients because wild oats are controlled before they emerge from the ground.”

According to Gowan Canada, just two wild oats per square foot can cut spring wheat yield by 15 per cent and four per square foot can cut yields by 24 per cent. Furthermore, the company says waiting until the two-to three-leaf stage of wild oats to control the can result in a drop in crop yields of 11 per cent. Waiting until the four to five leaf stage drops yields by 23 per cent.

To maximize wild oat control when using Avadex, Kunkel urges farmers to apply Avadex in the fall. “Avadex applied in standing stubble in the fall works exceedingly well. Growers need to wait until late in the fall when the average soil temperature at two inches (five centimetres) is less than 4 C. Avadex will not activate below (that temperature).”

“No incorporation is required. If there is heavy straw, a light harrowing may help to shake the Avadex down to the soil surface. Simply leaving the Avadex on the surface over winter and then seeding directly into the stubble gives the best control of wild oats, ” he says.

Avadex can be fall applied to chemfallow fields as well, and is registered for use in spring wheat, durum wheat, barley, canary grass, canola, mustard, sugar beets, flax (not in low-linolenic varieties) and dry peas (Extra Strength Avadex BW formulation only).

Kunkel points out Fortress can also be fall applied with no incorporation required. This product combines triallate, the active ingredient found in Avadex, with granular trifluralin to control not only wild oats but also green and yellow foxtail. It also provides suppression of kochia, lamb’s quarters, redroot pigweed, Russian thistle, and wild buckwheat. “This is a very interesting product, especially for canola growers, because it provides early season weed control which can result in substantial yield increases.”

Most farmers are familiar with both Avadex and Fortress and remember these as Monsanto products. In 2004 Monsanto sold the formulation, trademarks, and registration for triallate to Gowan, a provider of crop protection products headquartered in Yuma, Arizona. Gowan distributes Avadex and Fortress through UAP Canada.


Steve Larocque, agronomist, independent consultant and farmer from Three Hills, Alta., says, “nonincorporated, fall-applied Avadex, Fortress and Edge works really well and the addition of Group 8 and 3 herbicides in your herbicide rotation is a great way to address the development of herbicide resistant wild oats.”

Larocque points out the late fall application timing of these products is also an advantage as it reduces workload in the busy spring season. According to Larocque, you should wait until just before freeze-up to make sure the granules are activated as the soil warms in the spring instead of activating in the fall.

“It is important that the wild oats germinate in the treated Avadex layer. Growers who have been direct seeding for five to 10 years will find most of the weed seeds are now on the soil surface, so that is where the herbicide should be placed.”

He adds that the granular formulation of Avadex is a better fit for fall versus the liquid formulation. “Liquid Avadex can bind to the straw,” he says. “Make sure you seed below the treated Avadex layer to prevent crop damage. I have checked over 2,000 acres of direct seeded land that had Avadex applied in the fall without incorporation and have not seen any crop damage,” says Larocque.


Since Avadex, Edge and Fortress have been on the market for many years, there is very little recent performance data on these products. However, there were a number of studies done in the early 90s to determine the effectiveness of these products when applied without incorporation to lands under zero-tillage management

A three-year study at the Scott Research Station from 1989-1991 found wild oat control using Avadex with no incorporation was equal to that when using a single fall incorporation. It also found nonincorporated Avadex performed just as well as when it was incorporated twice (in the fall and spring). Wheat and barley yields were found to be higher from the non-incorporated trials. This was likely due to moisture conservation from not having to incorporate the herbicide.

A 1992 trial at Scott found wild oat control using both Avadex and Fortress was superior under zero tillage management than under minimum-or conventional tillage systems, and in 1994 and 1995 Dow Elanco (now Dow AgroSciences) evaluated non-incorporated, fall applied Edge and Treflan. In direct seeding applications, non-incorporated Edge averaged 91 per cent control of wild oats and eight other problem weeds listed on the label. Treflan gave an average 85 per cent control of these same nine weeds. However weed control dropped by seven to eight per cent in spring non-incorporated Edge and Treflan trials.

2010 will not only be remembered for the record rainfall in many areas, but also for a bumper crop of weeds. The cool wet weather of 2010 resulted in higher than normal weed populations. Many fields did not get seeded, some fields did not get sprayed, other fields have uncontrolled second flushes of weeds. As a result, the increase in weed seeds in the soil seed bank means 2011 weed pressures will likely be high. Maybe this is the fall when farmers should be looking at using a Group 8 or Group 3 fall-applied herbicide to try to get a handle on next year’s weeds before they become a problem.


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