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2019 Weed Watch: Reduce the Weed Seed Bank

January 4, 2019
This agronomic image shows young marestail

Marestail often overwinters and can prevent you from starting 2019 with a low weed seed bank. Apply a burndown herbicide to start managing marestail now.

Harvest may be over, but managing resistant weeds remains key. If resistant weeds go to seed, weather, machinery, livestock and wild animals can spread them farther. Managing your weed seed bank now is a critical component to next year’s weed management plan.

Overwintering Weeds to Watch

Seeds of several problematic weeds can remain viable in the soil for years, including:

Marestail (horseweed):

  • Marestail can produce up to 200,000 seeds per plant, which are highly mobile and easily spread to new areas.
  • According to one study, 59 – 91% of fall-emerging marestail plants survive winter.
  • Controlling marestail with a burndown herbicide mixed with a residual herbicide is critical.
  • Marestail has shown resistance to ALS inhibitors (Group 2) and glyphosate (Group 9), and is especially troublesome in no-tillage crop production systems.


  • Not only can waterhemp produce up to 1 million seeds per plant, its seeds can also survive in the soil for 7 to 10 years.
  • Six-way resistant waterhemp was found for the first time in Missouri in 2018.
  • Waterhemp has known resistance to glyphosate, photosystem II inhibitors (Group 5), ALS inhibitors, PPO inhibitors (Group 14), auxins (Group 4) and HPPD inhibitors (Group 27).

Palmer amaranth:

  • Capable of producing up to 600,000 seeds per plant, Palmer amaranth remains viable in the seed bank for up to 6 years.
  • This weed has shown resistance to ALS inhibitors, HPPD inhibitors when applied post-emergence, glyphosate, PPO inhibitors and photosystem II inhibitors.

Start Preparing for 2019 Weed Management

Syngenta recommends the following practices to start the new season with a low seed bank:

  • Plan ahead for your 2019 weed management program.
  • Scout fields to identify weeds that may have overwintered.
  • Apply a burndown herbicide to reduce the weed seed bank.
  • Apply a pre-emergence herbicide before crops emerge.
  • Don’t let weeds grow past 4” or grow to seed – they’ll become harder to manage.

It’s also important to keep in mind that new herbicide technologies should not be treated as a silver bullet for resistant weed management. Instead, new herbicides should be used as an additional tool in an integrated, comprehensive weed management program.

Diversify weed management strategies and use multiple effective sites of action (SOAs) to increase 2019 yield potential. As you make herbicide decisions for the year ahead, plan a full-season herbicide program to keep fields clean next year and into the future. Our Resistance Fighter® program provides local recommendations for efficiently managing weeds and weed resistance in your area.

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