Managing volunteer canola in tight rotations

The benefits of alternating herbicide-tolerant systems

By: Colleen Redlick

Maximizing canola production in tighter canola rotations requires planning that includes managing volunteer canola. A volunteer is any canola plant that grows from the seed of a previous crop. They can be viable for a couple of years in soil and a single volunteer can produce over 500 seeds.

Left unmanaged, volunteer canola can reduce a crop’s yield potential and have negative effects on both quality and integrity.

Decreased yield potential

  • Volunteers do not have the same genetic yield potential. Second generation seed can yield as much as 13% less that the original hybrids.
  • Volunteers compete with the crop for nutrients, water and light, reducing the crops yield potential during early development.
  • Emerged canola volunteers can provide a refuge for flea beetles, which can damage a seeded crop regardless of whether a seed treatment was used.
  • Volunteer seed that has been sitting in the soil can harbour diseases (blackleg, clubroot and sclerotinia), subsequently infecting the crop.

Quality and integrity

In addition to consequences in yield potential, volunteers can also introduce undesirable traits through cross pollination and seed contamination (Canadian Seed Trade Association, Fact Sheet). Left unmanaged, the persistence of canola volunteers that are not from the crop can also impact marketability of the harvested seed. (Canola Council, Canola Export Ready program)

Source: Canola Council of Canada, Canola Grower’s Manual, 2011.

Using wild mustard (a similar species to canola) as a stand-in for volunteers gives an idea of yield reduction based on volunteer density. At 5 wild mustard plants per m2, canola can lose 15% of its yield.

Volunteers can be introduced to a field in a number of ways:

  • Losses of seed through the combine at harvest can be up to 20 times the seeding rate for a crop.
  • Pod shatter during swathing and heavy wind or hail impact on a standing crop can add seed to a field.
  • Full tillage and the burying surface seed left after harvest can keep volunteer seed viable for years (dormancy).
  • Volunteer seed can also be transported field-to-field via equipment.

Scouting for volunteer canola.

It’s always recommended to scout early before seeding the crop to look for early germinating volunteers. Look for seedlings that are emerging between the rows; these will likely be volunteers. An easy way to confirm is to dig it up and look at the seed. If there is no coloured seed coat it means it’s untreated and therefore a volunteer.

Volunteer canola emerges early and can harbour flea beetle and seedling diseases.

Source: BASF video, Scouting for volunteer canola

Integrated management plan for volunteer canola

There are several things you can do to reduce the presence of canola volunteers in your field:

  • Keep records of the herbicides used, including years when canola is not being grown.
  • Manage your harvest, especially with respect to swathing timing and combine settings. Aim to reduce any canola seed returned to the field.
  • Promote the germination of any seed left on the soil after harvest. Germinated seed will not survive.

Rotating your HT canola system

If you have volunteer canola or anticipate having it in a canola sequence, the best recommendation is to rotate to a canola system that uses an alternative-mode-of-action system herbicide. The three main herbicide-tolerant (HT) canola systems use herbicides from three different group chemistries.

  • glyphosate (Group 9)
  • glufosinate (Group 10)
  • imidazolinones (Group 2)

Rotating between these three systems will help ensure volunteer canola can be controlled by the alternative in-crop system herbicide.

Including Clearfield® in your rotation

The Clearfield Production System for canola with Ares® herbicide provides an alternative mode of action for control of volunteer canola from the Group 9 and Group 10 herbicide-tolerant canola systems. Including it in the rotation can provide other benefits as well:

  • High-performance hybrids designed for competitive yields
  • Superior standability and harvestability for straight-cutting ease
  • Different maturities, resistance to disease and lodging along with other agronomic traits suitable for your operation
  • Pod-shatter resistance for better straight-cutting performance with newer varieties being developed
  • Consistent, reliable post-emergent weed control, including subsequent flushes of weeds like cleavers and wild mustard
  • Improved control of wild buckwheat, wild oats and lamb’s quarters

Tightened canola rotations require all growers to have an integrated management plan for reducing the losses in yield due to volunteers. Scouting early to keep a handle on any problems that may be present in your fields and planning to include all possible HT systems in your sequence can go a long way to helping maximize the success of your canola crops.

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