Flax is a small, upright plant that does not branch out (tiller) extensively or produce much biomass. It develops a short, branched taproot that will extend up to 1 metre (39 inches) in depth and 30 cm (12 inches) across. As a result of the minimal ground cover that flax provides, it is a poor competitor with weeds that are more aggressive and they can thrive via access to sunshine, moisture and nutrients.

Weeds don’t only affect crop yield, they also contribute to losses via dockage in grain samples and shipments. Removal of weeds also improves quality factors like oil content and iodine levels.

To see best results for weed control in flax and to minimize losses most effectively, removal should occur prior to the crop reaching 6 inches in height. Weeds in the seedling stage are easiest to control and there is a decreased risk to injury of the crop at the early growing stages. Crop injury can also occur in herbicide applications with low water volume and/or in hot conditions.

Since flax is a reasonably weed-intolerant crop, it is best to take a long-term approach for weed control with both cultural and chemical controls, where applicable. In terms of chemical control, timely pre-emergent herbicide applications, preferably with residual control, are ideal to get the flax crop off to a strong start. Some farmers find that seeding the flax crop a little later gives them a window for pre-seed or pre-emergent applications on those hard-to-control weeds. Following emergence, keeping an eye on the crop staging and weed pressure is crucial so that herbicides can be applied at an appropriate time.

Flax has a good selection of herbicides for all application timings. Always refer to Manitoba’s Guide to Field Crop Protection for up to date options, or refer to MCA’s Quick Herbicide Reference Guide.

Important considerations when determining a herbicide program include:

Pre-emergent herbicides give the crop the best chance to thrive as early as germination, and to get ahead of weed populations. Minimizing competition at this very early stage is crucial for the crop.

Post-emergent herbicides are limited to Groups 1, 4 and 6, which is not uncommon for special crops and it is a hurdle when considering weed control, especially in the age of weed resistance. Specific planning needs to occur in previous crops for weed control and with fall-applied or pre-emergent herbicide use.

Pre-and post-harvest herbicides are a valuable resource for long-term weed control planning, in flax and all other crops. This is great opportunity to look at perennial weed populations and target control when they are preparing for seasonal dormancy.

For more information on growing flax on the Prairies, see Flax Production Resources on our website.