The list of herbicide-tolerant soybean traits is growing as seed companies continue adding herbicide site of action resistance in an effort to control herbicide-resistant weeds and increase options to reduce the risk of off-target injury to nearby sensitive crops.

Doctors Travis Legleiter and J.D. Green, University of Kentucky Extension weeds specialists, prepared this article explaining soybean herbicide traits to consider when ordering seed for 2020.

The LLGT27 soybean has been available two years and has resistance to glufosinate and glyphosate, and contains an HPPD­inhibitor (Group 27) resistance event. These varieties have essentially only been available as a glufosinate- and glyphosate-resistant soybean because the HPPD herbicide, Alite 27, has yet to be registered by the EPA. Alite 27 will hopefully receive EPA approval by the 2020 season and be offered as a pre­emergence herbicide for use on LLGT27 soybean fields.

The LLGT27 varieties are best suited for fields that contain glyphosate-resistant marestail, Palmer amaranth, or waterhemp and heavy grass weed pressure. The strength of this trait package is the option to apply both glyphosate to control grass species and glufosinate to control the glyphosate­resistant weeds. The pending approval of Alite 27 will allow farmers to place another herbicide Mode of Action group on those fields with heavy Palmer amaranth and waterhemp pressure. These LLGT27 varieties are a great fit for fields with nearby specialty broadleaf crops or tobacco. LLGT27 are sensitive to dicamba, so injury from off target dicamba drift is possible.

Enlist E3 varieties became more widely available in 2019 and offer resistance to glyphosate, glufosinate, and 2,4-D. We expect acreages of these varieties to increase in the coming seasons. These varieties have a great fit on fields that are infested with glyphosate­resistant marestail, Palmer amaranth, or waterhemp, as well as heavy grass weed pressure. These varieties are also well suited for fields that are in close proximity to sensitive broadleaf crops as producers have the option to apply glufosinate and glyphosate, without 2,4-D, post-emergence.

2,4-D use on Enlist E3 soybean should be limited in fields that are in close proximity to crops sensitive to 2,4-D. Enlist E3 are sensitive to dicamba, so injury from off-target dicamba drift is possible.

The Roundup Ready 2 Xtend trait has been available since 2017 and has rapidly become the most popular herbicide resistance package despite some issues concerning its use. This technology has caused some division among the agriculture community due to off-target movement of dicamba during post-emergence applications to these soybean varieties. The Roundup Ready 2 Xtend trait package offers resistance to glyphosate and certain dicamba products.

Roundup Ready 2 Xtend varieties are best suited for those fields with heavy infestations of marestail, Palmer amaranth, and waterhemp that are glyphosate-resistant. Fields that contain widespread and other heavy winter annual weed pressure will greatly benefit from the ability to apply dicamba as the burndown treatment and plant without any delayed timing restriction.

Roundup Ready 2 Xtend varieties should be avoided in fields that are near specialty broadleaf crops, grapes, tobacco, and sensitive soybean varieties. Use caution when planting Roundup Ready 2 Xtend varieties into fields with heavy grass pressure. Researchers in Tennessee have observed significantly reduced control of grassy weed species with glyphosate when tank-mixed with dicamba due to suspected antagonism.

Approval is still pending for the Roundup Ready 2 Xtend Flex technology. It is the next generation of the Xtend

Portfolio and offers glyphosate, dicamba, and glufosinate resistance. These soybean varieties need approval from the European countries before being released for commercial use. The UK Weed Science program has had the benefit of evaluating this soybean event the last two seasons and believe they offer a very versatile package to Kentucky farmers. These soybeans have a good fit on fields with heavy infestations of glyphosate-resistant marestail, Palmer amaranth, or waterhemp. The XtendFlex offers much more flexibility with the addition of glufosinate as a herbicide option. The addition of glufosinate allows for these varieties to be planted in closer proximity of sensitive soybean and tobacco fields and still allow for a viable post-emergence herbicide option with glufosinate and reduced risk of off-target movement.

Clint Hardy is the Daviess County Cooperative Extension Service agent for agriculture and natural resources. His column runs weekly in the Agriculture section.

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