Soybean traits can help with herbicide selection03/05/2019 | Crop Production Research, Economics, Weed Issues
By Scott Nelson, On-Farm Network® Director
Because of the lack of development in new herbicide modes of action, the seed industry has focused on developing herbicide resistance traits to better manage weeds and weed resistance. To date, FMC is the only company that has announced discovery of a new herbicide mode of action for soybeans. It is expected that this new product will take 10 years to reach the market as it works its way through regulatory hurdles.
This means that farmers will have to make do with existing herbicides for at least a decade before a new herbicide mode of action is available for use. Several products, either on the market or coming soon, can help provide relief from herbicide-resistant weeds.
RoundUp Ready 2 Xtend® Soybeans: Introduced three years ago, this product continues to grow in popularity with farmers. Its trait system provides soybean resistance to glyphosate and dicamba herbicides. Reports of weed control from this product have been surprisingly good, especially when paired with a pre-emergence herbicide. The major drawback has been complaints of off-target movement of approved products containing dicamba into sensitive crops. To combat incidences of off-target loss, the EPA made significant label restrictions and training requirements for applicators.
Practices to reduce off-target loss of dicamba products are well documented, but two lesser-known practices could help alleviate dicamba drift:
- Using hooded sprayers. Research conducted by universities and Bayer have confirmed in published studies that the use of hooded sprayers significantly reduces herbicide drift up to 85 percent. Hooded sprayers can improve weed control by directing more product into the canopy. The downside of hooded sprayers is that a smaller boom size is necessary. Farmers that do much spraying near sensitive areas could consider using hooded sprayers to reduce risk.
- Reducing boom heights to 24 inches above the target. This simple and inexpensive practice has been shown to reduce off-target movement.
XTENDFLEX® Soybeans: While not yet available in 2019, farmers should be aware of Bayer’s intention to market this product soon. XTENDFLEX soybeans provide herbicide resistance to three modes of action: glyphosate, glufosinate (Liberty) and dicamba. This product may offer farmers some significant options for managing herbicide-resistant weeds as well as managing off-target injury to sensitive crops. A farmer may choose to use an approved dicamba product early post-emergence to control weeds when sensitive crops are at a lesser risk of injury. A second post-emergence pass of a glufosinate product provides another mode of action with good activity on surviving weeds.
Enlist E3™ Soybeans: This trait system provides soybean herbicide resistance to three modes of action: glyphosate, glufosinate and 2,4-D. The 2,4-D component of this technology must be the low volatile formulation provided by Corteva. Stewardship and attention to off-target loss of this herbicide system is required, like dicamba programs. This product will be available in limited quantities in 2019. Farmers are encouraged to take the necessary time to evaluate this product at various trainings and field days this summer.
LibertyLink® GT27™ Soybeans: GT27 soybeans provide resistance to glyphosate, glufosinate and isoxaflutole (Balance). Currently, there is no label registration for isoxaflutole. Developers of this system claim the trait protects soybeans from carryover of Group 27 herbicides (Calisto, Laudis). While isoxaflutole has potential to improve weed management in soybeans, over-reliance on this mode of action could shorten the timeline for resistance to develop. The use of isoxaflutole chemistry in corn following use on soybeans in the previous season is not recommended. Tank mixes of glufosinate and glyphosate have received conflicting reviews. Some studies report antagonism between glyphosate and glufosinate when applied together, while other studies have shown greater efficacy, but this is weed-specific. As the technology evolves, more evaluation will be needed on the merits of glyphosate and glufosinate tank mixes.
The University of Missouri recently conducted a study comparing weed control for the various herbicide trait systems. In Figure 1, note that waterhemp control was nearly equal for all the various trait systems, significantly greater than when glyphosate was used alone. This is important to farmers because it allows greater flexibility with their chosen herbicide trait system. Farmers should look for the best herbicide packages among the various trait systems for yield, disease resistance and price.
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