There are some good options for controlling glyphosate resistant weeds in soybeans. But do you know which herbicides to consider?
The following are specific recommendations from the 2020 South Dakota Pest Management Guide — Soybeans, published by South Dakota State University Extension Service.
Options include rotating to Liberty Link or dicamba-tolerant technology or using conventional herbicides. In Roundup Ready soybeans, consider using a full rate of a preemergence herbicide containing flumioxazin (Valor, Fierce, Afforia, etc) or sulfentrazone (Authority products, Sonic, etc.).
In no-till, burndown options may include Cobra (lactofen), dicamba-tolerant Liberty (glufosinate), or Gramoxone (paraquat). Cobra (lactofen) may be the most effective post-emergence option, but it should not be applied during stressful growing conditions.
Plan on scouting fields closely after soybean emergence and making any postemergence herbicide applications prior to the third soybean trifoliate.
The best management option may be to use preemergence herbicides such as flumioxazin products (Valor, Fierce, Surveil) or sulfentrazone products (Authority products or Sonic). Flexstar/Reflex (fomesafen), Avalanche Ultra/Ultra Blazer (acifluorfen), and Cobra (lactofen) may be the most effective postemergence tank-mix partners.
Glufosinate (Liberty/Cheetah) will control glyphosate-resistant waterhemp in Liberty Link soybeans, but applications must be made to small (less than 4 inches) waterhemp plants.
The Enlist (2,4-D) system works well on waterhemp but again waterhemp should be small, ideally no more than 4 inches tall. Labeled dicamba products will control glyphosate resistant waterhemp in Xtendimax soybeans, but applications must be made to small (less than 4 inches tall) waterhemp plants.
In Roundup Ready soybeans, consider using a preemergence herbicide that contains cloransulam (Authority First/Sonic or Surveil), metribuzin (Authority MTZ), fomesafen (Prefix), or flumioxazin (Valor, Afforia, Surveil) followed by a glyphosate tank-mix partner such as FirstRate (cloransulam) or Flexstar (fomesafen).
Do not apply Flexstar postemergence if Prefix was applied preemergence. Consider rotating to Liberty Link, dicamba tolerant or using conventional soybean herbicides.
In Roundup Ready soybeans, use 2,4-D ester in the burndown application before planting or use a preemergence herbicide that also has foliar activity such as saflufenacil (Sharpen or OpTill) or cloransulam (Authority First/Sonic or Surveil).
In Xtendimax soybeans, labeled dicamba products will provide control. For postemergence, consider tank-mixing FirstRate (cloransulam) with glyphosate.
Lambsquarter may be tolerant of glyphosate during adverse conditions, but resistance has not been confirmed in SDSU trials.
The best management option may be to use preemergence herbicides containing flumioxazin (Valor, Fierce, Afforia, etc.), sulfentrazone (Authority products, Sonic, etc.), or saflufenacil (Sharpen, Optill, etc.).
Thifensulfuron (Harmony, etc.) may be the most effective postemergence tank-mix partner, but it may stunt soybeans during periods of rapid growth. Cadet (fluthiacet) or Resource (flumiclorac) may be moderately effective.
The Enlist (2,4-D) system works well on lambsquarters but plants should be small, ideally less than 4 inches tall.