Flax TIPS: Planning for Harvest

August 23, 2016 0 Comments

Swath or straight-cut? Desiccant or pre-harvest herbicide? There are a number of factors to consider when selecting management practices for harvesting flax. The following is an overview of the benefits, challenges and ways to optimize harvesting flax.


Flax is well suited to straight-cutting due to low shattering risk (relative to canola) and seed bolls that develop high up on the plant. However, flax does cause some unique challenges due to the tough, fibrous nature of the straw. Cutter bars should be well maintained and sharp to prevent gumming up of the knife. Desiccation can be an alternative to waiting for natural dry down, such as when moist soil conditions result in stems staying green, or a hard killing frost. Straight-cutting should occur when mature seed is 10% or less seed moisture content, which is generally around 95-100% brown boll stage.


Swathing of flax has become less common, largely due to larger farm size and the availability of improved equipment which facilitates straight cutting, reduces labour and harvest time. However, swathing can still provide advantages over straight-cutting in some years. For example, swathing can be a good alternative to straight cutting if re-growth occurs in fall, such as when desiccation has not be used, there is a wet fall after a dry August or a lack of killing frost. Swathing should occur when bolls are 75 – 80 % brown (mature crop). Cutting prior to this stage can result in seed weathering, and reduced seed weights. Immature seeds can be damaged by frost at -3°C to -5°C range. To ensure drying and prevent movement by strong winds, stubble height should be 4 – 6 inches and rolling swaths is recommended.

Straight Cutting Swathing
  • Straight-cutting should occur when mature seed is 10% or less seed moisture content
  • Swath when bolls are 75 – 80 % brown (mature crop)
  • No risk of loss from flax rolling with strong fall winds
  • Good alternative to straight cutting if re-growth occurs
  • Facilitated bypre-harvest herbicides and desiccants
  • Maintain a stubble height of 4 to 6 inches
  • Maintain sharp knives on cutter bars to prevent gumming. Can cause wearing of equipment.
  • Roll swaths to prevent from rolling in high winds

Chemical Desiccation/ Preharvest Herbicides

Desiccants and preharvest herbicides can be a good option to facilitate crop dry down and ease harvest. However, it is important to note that both desiccants and preharvest herbicides do not speed maturity. Products should be applied only after the crop has reached physiological maturity (75% brown boll). Once dried down, the crop is at risk of boll shattering and should be combined as soon as possible after samples test 10% moisture.

If perennial weeds are a problem then glyphosate may be a good option to control weeds while also drying down the crop. This can also be beneficial to prevent green material from entering the combine. Glyphosate can also reduce plant re-growth because of the systemic mode of action of the product. Seed growers, or those planning on saving seed for the following year should not use glyphosate as it can reduce seed germination. Diquat does not cause any effects on germination.

Desiccants are generally faster acting, especially as temperatures have begun to drop which may cause reduced efficacy of glyphosate. If the plant has matured (brown bolls) but stems remain green, diquat may be advantageous since the product does not require an actively growing plant. However, benefits must be weighed against the higher costs associated with the product.

Product Glyphosate Diquat
Whatis it? Pre-harvest herbicide Desiccant
Mode of Action Systemic Contact
Effects of Growing Conditions Best results when plants/weeds are actively growing and daytime temperatures are around 20°C. Best results when conditions are cloudy or in the evening.
Application Timing 75% brown bolls 75% brown bolls
Pre-harvest Interval 7 to 14 days (Under ideal conditions) When sample tests dry
Pros and Cons
  • Slow acting
  • Kills crops and weeds, works on perennial weeds
  • Best on actively growing plants
  • Does not speed maturity
  • Negatively affects seed germination
  • Low cost
  • Fast acting
  • Desiccates top growth of crops and weeds
  • Best on senescing plants
  • Does not speed maturity
  • Does not affect seed germination
  • High cost

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