How to Control Waterhemp in Corn and Soybeans

/_uploads/images/ts-waterhemp.jpgWaterhemp is an aggressive annual broadleaf weed that is one of the most common weeds in the Midwestern United States and is quickly becoming one of the most troublesome weeds for corn and soybean growers in southern Ontario and western Quebec. Waterhemp is highly competitive with a rapid growth rate of most weeds and crops, and has developed resistance to multiple herbicides. Produced seed can remain viable in the soil for over four years and therefore, population density can be extremely high. Waterhemp can also be devastating to yields, causing losses of up to 38% in corn and 73% in soybeans.1 No matter which trait system you’re using, make sure two or more effective sites of action are part of your weed management strategy this season.




Early season weed management is critical for waterhemp management in corn and soybeans. Growers should use overlapping applications of the best pre-emergent residual herbicides, followed by the best post-emergent herbicide with multiple sites of action in both applications.

In Roundup Ready 2 Xtend® soybeans, start with a pre-application of Bifecta™ herbicide, then follow up with an early to postemergent application of Roundup Xtend® herbicide with VaporGrip® Technology. Bifecta™ contains metribuzin (Group 5) and flumioxazin (Group 14), and it can be used pre-emergent in all soybean varieties.

In Genuity® Roundup Ready 2 Yield® soybeans, the best way to control waterhemp is through prevention. The best method is with pre-applications of herbicides with multiple effective sites of action for good residual control, making Bifecta™ both a safe and effective option.

Here are a few tips to help maximize the performance of soil-applied pre-plant/pre-emergent herbicides:

  • If waterhemp is present at burndown, tank mix dicamba or 2,4-D with Roundup WeatherMAX® or Roundup Transorb® HC herbicides. Be sure to consult product labels for planting interval restrictions.
  • Select pre-plant/pre-emergent herbicides based on the weed spectrum in each field.
  • Use full-labelled rates of pre-plant/pre-emergent herbicides.
  • Consult each product label to identify precautions and restrictions for premix products that have chlorimuron as an active ingredient.
  • Scout each field regularly to determine in-crop application timing and to identify waterhemp that may have escaped the previous application or emerged late.




Waterhemp can rapidly grow and reproduce and the opportunity to have multiple generations within a given season is increased. In any weed management program, no one herbicide should be utilized as the sole mechanism used to control weeds. A single female pigweed plant can produce anywhere from 35,000 to 1,200,000 seeds. And because waterhemp species are dioecious, two waterhemp plants, one male and one female, will always mix genes during reproduction, increasing its potential to spread resistance.2 Protect crop yield and the efficacy of herbicide program, by tank mixing herbicides with multiple effective sites of action. Here are tank-mix options to consider:

Roundup Ready 2 Xtend® Soybeans
PP/PRE (conventional tillage) Bifecta™, Boundary® LQD, Fierce® or Focus®
PP/PRE (no tillage) Roundup Xtend® with VaporGrip® Technology + Bifecta™, Boundary® LQD, Fierce®, Focus®
POST (conventional or no tillage) Roundup WeatherMAX® + XtendiMax® with VaporGrip® Technology, or Roundup Xtend® with VaporGrip® Technology as needed
Genuity® Roundup Ready 2 Yield® Soybeans
PP/PRE (tank mixed with Roundup Transorb® HC) Boundary® LQD, Fierce®, Focus®
POST (tank mixed with Roundup WeatherMAX®) Reflex®
Corn Hybrids with Roundup Ready® 2 Technology
PP/PRE (tank mixed with Roundup Transorb® HC) Focus®, Primextra® II Magnum®, Converge® XT, Lumax® EZ, Callisto® + atrazine
POST (tank mixed with Roundup WeatherMAX®) Marksman®, Distinct®, Banvel® II, Armezon®, Callisto® + atrazine


Scout early and often this season to keep a close eye on the waterhemp situation in your fields. And be sure to not confuse it with other pigweed species which look very similar, especially in the seedling stage; knowing the species present on any given field can help to further tailor your weed management program. Like any tough-to-control weed, following good agronomic practices is key to preserving the efficacy of the best crop protection tools available. Agronomic practices, like row spacing and planting rate, will enhance the competitiveness of your crop and improve the consistency of your herbicide program.


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