Managing Weed Seed Banks

By Keana Boere, Student, North Battleford

The weed seed bank is the reserve of viable weed seeds present throughout the soil profile. Seeds are added to the seed bank by seed rain, when mature weed seeds fall from the mother plant, or by other factors such as equipment, people, wind or animals bringing weed seeds from nearby locations. Seeds in the bank are either non-dormant and ready to germinate or they are dormant and waiting for favorable environmental conditions for germination. Of the many seeds in the bank, few will actually germinate. Many are eaten by birds or insects, decay or die before they have the opportunity to germinate. Seeds that do survive will germinate and grow into adult plants which will produce mature seeds that contribute back to the seed bank through seed rain.

Preventing weed seeds from entering the bank is the best way to control and deplete the bank. If new weed seeds are not added to the bank, eventually reserves in the soil become depleted. Several management techniques can be used to control weed seed banks.

  • Herbicides are an effective weed control option, especially when used on young weed seedlings. Preventing weeds from flowering and releasing seed ensures that their seeds are not added to the seed bank.
  • Physical impact mill attachments on combines provide harvest weed seed control (HWSC). A well-known piece of HWSC equipment is the Integrated Harrington Seed Destructor. There are a few other models in production, including the Seed Terminator, the Saskatchewan produced Redekop Seed Control Unit and TecFarm’s WeedHOG. Impact mills crush and destroy weed seeds before they exit the combine with chaff and other residues. Most impact mills are over 95 per cent effective at destroying weed seeds that enter the mill. Crushed seeds are no longer viable and will not germinate and therefore, do not contribute to the seed bank.
  • Diversifying crop rotations helps to break weed cycles that have formed over time. Annual weeds are usually a problem in annual cropping systems, while perennial weeds are usually a problem in perennial crop systems. Switching to a perennial crop can help deplete the seed bank of annual weed species.
  • Strategic tillage can be used to control a weed problem in a specific area and to promote weed seed germination from the seed bank. Tillage exposes weed seeds to warmer temperatures and more light, which promotes germination. Weed seeds that germinate due to the tillage pass can then be controlled as seedlings before seeds are set.

For more information on weed seed banks or weed control, contact your local crops extension specialist or call the Agriculture Knowledge Center at 1-866-457-2377.

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