Farmer’s interest in planting dicamba-tolerant soybeans continues. There are a number of reasons a farmer may choose to plant dicamba-tolerant soybeans, but a primary one is to potentially be part of their 2017 weed management plan to help in the control of glyphosate-resistant weeds. However, a word of caution, dicamba is currently NOT labeled for application to soybeans at planting or postemergence (read more below).
In an effort to help answer some of these questions, a yield performance trial was planted near Rochester, MN, in a Port Byron silt loam. The study included 14 dicamba-tolerant entries and four glyphosate-tolerant standards for comparison. Trials were planted on May 5, 2016 with a 4-row John Deere 7000 planter equipped with cone units. The seeding rate was 150,000 seeds per acre with seed planted at a depth of 1.5 inches in 30 inch rows. Plots were four rows wide by 22 feet in length and the center two rows of each plot were machine harvested on October 4, 2016.
Soybean yield results
Tables 1 and 2 provide the yield for the dicamba-tolerant soybeans entries at 13% moisture by entry and yield rank, respectively. The dicamba-tolerant soybean entries averaged 72.8 bu/a, ranging from 64.4 – 80.2 bu/a, while the glyphosate-tolerant entries averaged 75.1 bu/a, ranging from 70.0 – 80.8 bu/a.
Considerations when planting dicamba tolerant soybeans in 2017
Label concerns
Monsanto’s Roundup Ready 2 Xtend™ soybean, which is tolerant to both glyphosate and dicamba, is currently available for purchase. While this technology will eventually offer another option for controlling glyphosate-resistant and other tough-to-control weeds, there are still label concerns for the 2017 growing season.
Dicamba is NOT currently labeled for application on these soybeans at-planting or postemergence. Dicamba is currently labeled ONLY for burndown applications prior to planting, with a required wait time of 14 to 30 days before planting, even if the variety is dicamba-tolerant. Any other applications to soybean are in violation of federal and state law and may result in enforcement actions, and additional liability to the producer for off-target movement. One only needs to look at what happened in more southern states during the 2016 growing season, where older formulations of dicamba were illegally applied to dicamba-tolerant soybeans, and drift onto non-tolerant crops occurred. Thousands of acres have been affected, leading to litigation, fines, and proposals for further regulation.
Low-volatility dicamba formulations developed for use with tolerant soybeans are still awaiting approval. It is unknown when this label will be granted approval and if it will be granted in time for the 2017 growing season.
Use an integrated approach and start with a solid foundation
Due to uncertainty with the herbicide labeling, growers planning to utilize the dicamba system in the control of glyphosate-resistant weeds in soybean might want to consider alternative strategies. Options might include rotating to a different crop or planting a LibertyLink variety and applying glufosinate to control the problem weeds.
As always, an integrated approach that includes both chemical and non-chemical strategies is essential for managing difficult weeds, seedbanks and herbicide resistance. A diversified program is also a key component of an effective weed management – overreliance on any one technology is never recommended for effective, long-term weed control. (University of Minnesota Extension Regional Office, Rochester, and Southern Research and Outreach Center, Waseca, MN).
Table 1. Soybean yield (13% moisture) by entry of dicamba-tolerant compared to glyphosate-tolerant standards at Lawler farm, Rochester, MN, harvested October 4, 2016.
| No. | Entry name | Maturity | Moisture | Yield | ||
|---|---|---|---|---|---|---|
| percent (%) | bu/a | |||||
| 1 | Asgrow AG12X6 | 1.2 | 12.1 | cd | 72.8 | b-e |
| 2 | Asgrow AG17X6 | 1.7 | 12.0 | efg | 64.4 | f |
| 3 | Asgrow AG20X7 | 2.0 | 12.0 | efg | 70.3 | cde |
| 4 | Asgrow AG21X7 | 2.1 | 11.9 | fg | 80.2 | a |
| 5 | Croplan RX1466 | 1.4 | 12.1 | c-f | 68.4 | ef |
| 6 | Croplan RX1836 | 1.8 | 12.0 | c-g | 73.3 | bcd |
| 7 | Dahlman 6713XN | 1.3 | 12.0 | efg | 71.4 | cde |
| 8 | Dahlman 6717XN | 1.7 | 12.0 | c-g | 70.8 | cde |
| 9 | Dahlman 6721XN | 2.1 | 12.0 | efg | 76.7 | ab |
| 10 | Gold Country 2026X | 2.0 | 11.9 | g | 77.4 | ab |
| 11 | Pioneer P19T55X | 1.9 | 12.3 | ab | 74.2 | bcd |
| 12 | Pioneer P21T89X | 2.1 | 12.1 | c-f | 73.8 | bcd |
| 13 | Pioneer P22T24X | 2.2 | 12.3 | a | 73.4 | bcd |
| 14 | Producers Hybrids 2115NRX | 2.1 | 12.0 | efg | 71.8 | cde |
| 15 | Croplan R2C1950 | 1.9 Standard | 12.1 | cde | 80.8 | a |
| 16 | Asgrow AG1733 | 1.7 Standard | 11.9 | fg | 74.9 | bc |
| 17 | Pioneer P15T46R2 | 1.5 Standard | 12.2 | bc | 70.0 | de |
| 18 | Stine 20RD20 | 2.0 Standard | 12.0 | d-g | 74.8 | bc |
| LSD (p=0.10) | 0.1 | 4.6 | ||||
| Mean yield dicamba entries (1-14) | 12.1 | 72.8 | ||||
| Mean yield glyphosate tolerant entries (15-18, standard) | 12.1 | 75.1 | ||||
| Means followed by the same letter are not significantly different at the p=0.10 level | ||||||
Table 2. Ranked soybean yields (13% moisture) of dicamba-tolerant compared to glyphosate-tolerant standards at Lawler farm, Rochester, MN, harvested October 4, 2016.
| No. | Entry name | Maturity | Moisture | Yield | ||
|---|---|---|---|---|---|---|
| percent (%) | bu/a | |||||
| 4 | Asgrow AG21X7 | 2.1 | 11.9 | fg | 80.2 | a |
| 10 | Gold Country 2026X | 2.0 | 11.9 | g | 77.4 | ab |
| 9 | Dahlman 6721XN | 2.1 | 12.0 | efg | 76.7 | ab |
| 11 | Pioneer P19T55X | 1.9 | 12.3 | ab | 74.2 | bcd |
| 12 | Pioneer P21T89X | 2.1 | 12.1 | c-f | 73.8 | bcd |
| 13 | Pioneer P22T24X | 2.2 | 12.3 | a | 73.4 | bcd |
| 6 | Croplan RX1836 | 1.8 | 12.0 | c-g | 73.3 | bcd |
| 1 | Asgrow AG12X6 | 1.2 | 12.1 | cd | 72.8 | b-e |
| 14 | Producers Hybrids 2115NRX | 2.1 | 12.0 | efg | 71.8 | cde |
| 7 | Dahlman 6713XN | 1.3 | 12.0 | efg | 71.4 | cde |
| 8 | Dahlman 6717XN | 1.7 | 12.0 | c-g | 70.8 | cde |
| 3 | Asgrow AG20X7 | 2.0 | 12.0 | efg | 70.3 | cde |
| 5 | Croplan RX1466 | 1.4 | 12.1 | c-f | 68.4 | ef |
| 2 | Asgrow AG17X6 | 1.7 | 12.0 | efg | 64.4 | f |
| 15 | Croplan R2C1950 | 1.9 Standard | 12.1 | cde | 80.8 | a |
| 18 | Stine 20RD20 | 2.0 Standard | 12.0 | d-g | 74.8 | bc |
| 16 | Asgrow AG1733 | 1.7 Standard | 11.9 | fg | 74.9 | bc |
| 17 | Pioneer P15T46R2 | 1.5 Standard | 12.2 | bc | 70.0 | de |
| LSD (p=0.10) | 0.1 | 4.6 | ||||
| Mean yield dicamba entries (1-14) | 12.1 | 72.8 | ||||
| Mean yield glyphosate tolerant entries (15-18, standard) | 12.1 | 75.1 | ||||
| Means followed by the same letter are not significantly different at the p=0.10 level | ||||||
Source: University of Minnesota, Extension