The number of acres planted to soybean in southwest North Dakota are increasing each year. Controlling weeds in these soybeans will be critical to successful production. As these soybeans will be planted under no-till, selection of appropriate pre-plant or at-planting herbicides will be necessary to reduce weed interference and maximize yield, especially considering the low rainfall environment where yield is already limited. As many of the acres planted in southwest
North Dakota will be with glyphosate-resistant varieties developed through the NDSU Soybean Breeding Program, pre-emergence weed control will be extremely important for controlling difficult weeds as postemergence options will be limited. Weeds such as kochia and wild buckwheat are difficult to control with glyphosate alone, especially if they exceed 2 to 3 inches in height. Thus, it is essential that these weeds be controlled as much as possible through pre-plant burndown and preemergence herbicide applications. Trials will be conducted to evaluate timing of preplant herbicides for control of weeds and for soybean tolerance, Herbicide treatments will be applied 0, 1, and 2 weeks prior to planting. These treatments will be followed by glyphosate application in-crop at 2 weeks after crop emergence. Trials will be -visually evaluated for weed control and soybean injury at 1, 3, and 5 weeks after emergence. Soybean density will be measured at 3 weeks after emergence and soybean height will be measured at 5 weeks after emergence. Soybean yield will be measured by harvesting with a plot combine upon crop maturity.

1) Evaluate pre-plant and preemergence herbicides for control kochia and wild buckwheat in soybean
2) Evaluate response of soybean to pre-plant and preemergence herbicides
3) Evaluate soybean yield in response to herbicide applications for kochia and wild buckwheat control

Research results will be presented at crops day and county extension meetings. Research will also be published in annual reports and as journal articles in peer-review journals.

Update:
A trial was conducted at the Hettinger Research Extension Center to evaluate timing of herbicide application as well as different herbicide combinations for weed control in soybean. Treatment timings were 2 weeks before planting, 1 week before planting, and at planting. For these treatment timings the following preemergence herbicide treatments were evaluated: 1) Valor (flumioxazin) at 3 oz/A (0.75 lb ai/A), 2) Valor (flumioxazin) + Zidua (pyroxasulfone) at 3 + 5 oz/A (0.75 + 0.163 lb ai/A), 3) BroadAxe XC (sulfentrazone + metolachlor) at 32 oz/A (0.175 + 1.58 lb ai/A), and Authority Supreme (sulfentrazone + pyroxasulfone) at 9.8 oz/A (0.16 + 0.16 lb ai/A). These preemergence treatments were all tank mixed with glyphosate (Roundup Powermax 3) at 20 oz/A (0.75 lb ae/A) plus ammonium sulfate (AMS) at 8.5 lb per 100 gallons spray solution, plus adjuvant (Dynast HSOC) at 1% v/v. These treatments were compared with an untreated control and some other standard treatments; dicamba (Xtendimax) at 22 oz/A (0.5 lb ae/A) plus glyphosate (Roundup PowerMax 3) at 20 oz/a (0.75 lb/a) applied at planting, dicamba plus glyphosate at the same rates applied at the V1 growth stage, glyphosate at the same rate applied both at planting and at the V1 growth stage, and glyphosate plus BroadAxe at the same previous rates at planting followed by glyphosate at the V1 growth stage. AMS was not included in treatments containing dicamba. All treatments, including the controls were treated with glyphosate (Roundup PowerMax 3) at 20 oz/A on August 2, after all evaluations had been taken. Soybean were planted on May 27, 2022 in 30-inch row spacings using a John Deere planter at a seeding rate of 100,000 seeds/A at a depth of 2 inches. Soybean inoculant was included with the seed. In the seven days following treatment application, there was 1.24 inches of rain following the 1st application timing, 0.5 inches following the 2nd application timing, 0.36 inches following the 3rd application timing, and 0.02 inches following the postemergence treatment timing (V1).
Valor alone provided poor control of kochia, regardless of application timing. The addition of Zidua slightly increased kochia control at all application timings, but these increases were not statistically significant. BroadAxe also provided poor control of kochia, regardless of application timing. This was somewhat surprising as this treatment typically provides good to excellent control of kochia. The best control of kochia was through application of Authority MTZ, with 78 to 85% control of kochia. Xtendimax applied at planting provided poor control of kochia, however, delaying application until the V1 stage controlled kochia 83%. A split application of glyphosate at planting and at V1 provided fair control of kochia (78%). Glyphosate plus BroadAxe at planting, followed by a second glyphosate application at the V1 growth stage resulted in 87% control of kochia. Control of common mallow with Valor was inconsistent. The addition of Zidua to Valor provided better and more consistent control of common mallow. Broadaxe provided only fair control of common mallow. Authority Supreme and Authority MTZ provided good control of common mallow (80 to 92%), Xtendimax at planting provided poor control of common mallow, but delaying treatment to the V1 growth stage improved control. Split application of glyphosate, with and without Broadaxe provided the best control of common mallow. Annual grasses (green foxtail and barnyardgrass) were controlled best with treatments that included pyroxasulfone and were generally improved at the at-planting timing compared with earlier timings. The V1 application of Xtendimax and the split applications of glyphosate, with and without Broadaxe, also provided good to excellent control of these annual grasses.
Nearly all treatments improved yield compared to the untreated control (the lone exception being Valor applied 1 week prior to planting). The treatment with the highest soybean yield was the at planting application of Authority MTZ, although yield was statistically similar to earlier applications of Authority MTZ, the split application of glyphosate, Authority Supreme applied 1 week before planting, and Valor plus Zidua applied 1 week before planting.
The primary focus of this trial was to evaluate kochia control in no-till soybean in western North Dakota. The cool and wet spring of 2022 made it difficult to control this weed which remained small over an extended period with multiple emergences during the early growing season. Best control was found using combinations of sulfentrazone with either metribuzin or pyroxasulfone, or with split applications of glyphosate or with the V1 application of dicamba. The late application of glyphosate (on August 1st) over all treatments was successful at controlling weeds (including kochia) that had escaped previous herbicide applications. Without this application, soybean yield would have been further reduced. This trial is being repeated in 2023 to further evaluate the response of weeds and soybean to these herbicide treatments.

View uploaded report

Update:

View uploaded report

A trial was conducted to compare different herbicide treatment along with different herbicide timings for week control in soybean in southwest North Dakota. Trials were conducted under no-till farming practices. Several timings of application were compared to evaluate crop safety and levels of weed control. These herbicides compared in this trial included active ingredients that would control existing weeds as well as provide residual control of weeds that had not emerged at time of application. These timings included two weeks before planting, one week before planting, or at planting. The herbicides that were compared included flumioxazin (Valor EZ), flumioxazin plus pyroxasulfone (Valor plus Zidua SC), sulfentrazone plus metolachlor (BroadAxe/Spartan Elite), sulfentrazone plus pyroxasulfone (Authority Supreme), and sulfentrazone plus metribuzin (Authority MTZ). All of these treatments were tank-mixed with glyphosate. These treatments were compared with two applications of glyphosate (at planting and at the V1 growth stage of soybean (when the first trifoliate leaf is fully expanded), along with dicamba (XtendiMax) plus glyphosate applied either at planting or at the V1 growth stage. These treatments were also compare to an untreated control where no herbicide was applied and with a weed free control where weeds were controlled throughout the growing season. Glyphosate was applied across all treatments in this trial at the R1 soybean growth stage (first stage of flowering).
There was no measurable difference in weed control due to the timing of herbicide application. Kochia control was best with application of Authority Supreme, or Authority MTZ, regardless of timing, or with the V1 application of XtendiMax plus glyphosate, or with two application of glyphosate (at planting and at V1). These treatments also resulted in the highest soybean yield, except the Xtendimax treatment where yield was reduced perhaps due to weed competition prior to herbicide application. Valor alone provided poor control of kochia and resulted in reduced soybean yield due to wee competition. The key take-away from this trial is that there was a benefit to tank-mixing residual herbicides whether at planting or when applied one or two weeks before planting. This advantage was greatest when weeds, especially kochia, was controlled. Although soybean yield resulting from two applications of glyphosate was similar to results of using soil residual herbicides, there is an increased risk of weed control failure due to the increasing occurrence of glyphosate resistant weeds, including kochia, that are becoming more common. Tank-mixes that include both residual herbicides that control weeds before they emerge and postemergence herbicides, that control weeds that are already present in a field reduces risk of weed control failure and reduces risk of developing herbicide resistant weed populations.

The expansion of soybean acres into southwest North Dakota will require increased knowledge of weed control under environment conditions and no-till cropping system of southwest North Dakota. Identifying herbicides programs that will effectively control difficult weeds in no-till soybean will help to increase profitability of growing soybeans in a difficult environment for soybean.