Legend Seeds Blog

Weed Control After a Prevent Plant Season

Many areas within the corn belt experienced a wet growing season and, in some cases, there were many acres that did not get planted. Managing these “idle” acres is as important as managing an actual crop. Weed management is an important step in this process as we head into the upcoming growing season.

Factors to Consider:

  • Emerging Corn FieldThe overall effectiveness of weed control in the year that prevent plant was taken.
  • Did weeds go to seed?
  • The weed spectrum in fields where prevent plant was taken.
  • The crop grown following prevent plant will dictate which herbicides will be effective.

Action Plan:

The year following prevent plant is going to require multiple applications of herbicide to
control weeds. [1] A one pass herbicide program will likely not be enough to get desired weed control, especially in row crops such as corn and soybeans. An effective weed control program for corn and soybeans should include the following:

  • Pre-Emergent Herbicide:  Apply a pre-emergent herbicide and/or burndown before
    or after planting. Do not cut rates on pre-emergent herbicides. Use supplier and retail recommendations to apply the proper herbicide rates to get the longest residual possible.
  • Scouting:  Scout intensively before making a post-emergent herbicide application.
    Depending on what cover crop was used the prior year and where it came from, there is a possibility of inheriting new, noxious weeds into the field. Some examples of noxious weeds are:
    • Roundup Ready® canola seeds, which are extremely hard to control in corn and
    • Palmer Amaranth is a well-known weed that has over time migrated up into the
      northern states. Cover crops/CRP mixes from the south have been known to carry Palmer Amaranth seeds and can be overlooked until the problem arises in area fields.
  • Post-Emergent Herbicide:  Be timely with post-emergent herbicide application. Do not let any weeds get larger than six inches tall. Larger weeds are tougher to control with any class of herbicide. For best control of most broadleaves, dicamba and HPPD’s are known to be solid options in corn. Broadleaf control in soybeans is trickier, depending on what traits are in the soybeans. Dicamba is the best option in Roundup Ready® Xtend soybeans, and approved 2,4-D formulations are the best option in Enlist E3™ soybeans. [3]
  • Residual Herbicides:  Adding an overlapping residual herbicide when spraying post-emergent [2] is a sound practice. This method adds approximately three to four weeks of extended soil herbicide activity to keep weed seeds from even germinating. Acetochlor and metalochor based herbicides provide good weed control and soil residual, while providing in season crop safety to corn and soybeans.


There are many challenges to managing prevent plant acres. Weed control in the following crop grown should be a multiple step program. The prior year's weed control will play a large role in how effective the current year’s weed program will work. Weeds can be the ultimate yield robber in most row crops. Having a detailed plan and executing different modes of action site herbicides is the best way to attain clean fields following a prevented planting year.