Common Preharvest Questions in Flax

What is the staging for a preharvest or desiccation in flax?

Flax is considered physiologically mature when 75% of the bolls (in the field or on a plant) are brown and the boll segments have begun to separate. This is a visual rating that corresponds to a grain moisture content of around 30% and is known as the 75% boll turn or 75% brown boll stage.

Flax Maturity Ratings Sask Flax

Figure 1: Flax Maturity Ratings. Credit: SaskFlax

What is the difference between a preharvest aid and a desiccant?

Two types of chemicals are available to assist with flax harvest management: pre-harvest herbicides (sometimes called harvest-aids) and desiccants.

  • Pre-harvest herbicides are non-selective systemic herbicides that provide late season perennial weed control and may improve the harvestability of the crop by reducing the amount of green material in the field.
  • Desiccants are non-selective herbicides that rapidly dry down the crop and weeds to allow for an earlier harvest.

Comparison between pre harvest herbicide and desiccant characteristics Sask Flax

Figure 2: Comparison between preharvest herbicide and desiccant characteristics. Credit: SaskFlax

Can we use glyphosate as a preharvest aid?

Since it does terminate the crop, preharvest glyphosate may assist with stem dry-down and harvestability, however it is expected that the effects of glyphosate applied alone on flax dry-down can be slow and potentially inconsistent depending on environmental conditions. This all being said, at this time, it is not a recommendation of Manitoba Crop Alliance to apply glyphosate as a preharvest aid due to inconsistent results with maximum residue limit (MRL) testing. If a producer must use glyphosate, it is strongly recommended to speak with their grain buyer to determine if a glyphosate application to their flax will be a marketing concern.

What are the current registered preharvest aids and desiccants for flax in Manitoba?

Preharvest chemicals registered for use on flax Sask Flax

Figure 3: Preharvest chemicals registered for use on flax. Credit: SaskFlax


SaskFlax: Preparing for Harvest, July 2018.

Indian Head Agricultural Research Foundation: Pre-harvest Weed Control and Desiccation Options for Flax, 2019.

SaskFlax: Flax Markets and Maximum Residue Limits, April 2022.

Article written by Morgan Cott, Agronomy Extension Specialist – Special Crops with Manitoba Crop Alliance