Weeds can be a serious problem in flax if left uncontrolled. Because flax does not shade the ground as much as cereal grains, weeds have an excellent chance to develop. Some weeds like wild buckwheat and red root pigweed are luxury users of nitrogen and will rob the flax crop of needed soil nutrients. Weeds not only compete with the growing flax crops to reduce yields, but also cause losses from dockage in seed shipments. Dockage amounts to thousands of tonnes annually and is charged directly against marketing costs.
Benefits of Early Treatment
Early removal of weeds is necessary to minimize crop losses caused by weed competition. Weeds in the seedling stage are more easily controlled by herbicides than at any other growth stage, and early treatment usually decreases the risk of injury to the flax crop. Risk of injury is also reduced by using correct water volumes, usually 110 l/ha (10 gal./ac.). The performance of many herbicides can also be affected by soil moisture conditions, air and soil temperatures, and other environmental factors.
Many herbicides are available for the control of weeds in flax. Herbicides approved for flax are not necessarily approved for solin. As of 2001, only a limited number of herbicides are registered for use on solin. Additional herbicides are currently being evaluated for possible future registration. Contact your local agricultural representative or chemical company agent for information.
Herbicide Application Periods
There are three different herbicide application periods for the control of weeds in flax.
Pre-emergent herbicides include pre-plant soil-incorporated herbicides, and herbicides applied to weeds that emerge before the crop.
Spring post-emergent herbicides (see provincial weed control guide for recommended product brands) are most effective when the weeds are in the seedling stage. These herbicides are applied after the weeds have emerged and the flax seedlings are 2 to 12 cm (1 to 5 in.) tall. Check the growth stages of both the crop and the weeds, and then follow recommended instructions on the herbicide label.
All post-emergent applications of herbicides must be applied within the pre-harvest interval indicated on the herbicide labels. This ensures that herbicide residues are reduced to acceptable levels when the crop is harvested.
Formulations of glyphosate registered (see provincial weed control guide for recommended product brands) for pre-harvest are applied when the flax is ripe, to control perennial weeds before the weed stems are cut when harvesting.
Weed Resistance to Herbicides
When choosing a product for weed control, records from previous years must be checked to ensure that the same herbicide (or members of the same herbicide group) is not used year after year on the same field. Frequent use of a herbicide group may lead to the development of resistance to that group of herbicides by a weed species.
Control of Volunteer Flax in Field Crops
Flax is not a strong competitor, so volunteer flax does not usually result in yield losses in competitive crops like cereals and canola. However, it can cause considerable difficulty at harvest time because it can remain green long after the crop is mature. This interferes with harvesting and can cause grain storage problems.
There is no herbicide that will provide sufficient control, or even suppression, of volunteer flax in broadleaf crops. However, quinclorac herbicide provides excellent control of volunteer flax in wheat. Quinclorac provides control of cleavers and a new mode of action for green foxtail control. Products or mixtures that contain dichlorprop (see provincial weed control guide for recommended product brands) will provide some suppression of volunteer flax in cereal crops. Use the maximum recommended rates. Products that include 2,4-D LV ester will have slightly more effect on the flax than 2,4-D amine or MCPA.
Because of the poor level of control likely to be achieved with herbicides, cultural practices are important in minimizing problems caused by volunteer flax. A competitive cereal crop managed for maximum competitiveness (early, shallow seeding; adequate, banded fertilizer; maximum seeding rate for the area) and treated with one of the herbicides mentioned above, should maximize the level of suppression.
Weed control recommendations for flax are published annually by provincial departments of agriculture. For these publications and for the latest information and specific recommendations for your area, consult your local agricultural representative or weed supervisor.
Always read and follow label instructions carefully when using herbicides.