Flax

Flax herbicide options are somewhat limited. Establishment of good uniform dense flax stand is a great way to begin a weed control program. Grass weed control is good with available grass herbicides used alone or in combination with broadleaf herbicides. Our biggest weed problems in flax weed control in the past years have been poor control of redroot pigweed and kochia. Bromoxynil plus MCPA does well on small weeds but gives poorer control on larger weeds and it does not control weeds that emerge after application. Spartan is a good solution for these weeds providing residual control for 3-4 weeks. Research during the past three years has shown greater than 90% control of pigweed and kochia with Spartan at times. Spartan is able to control kochia and redroot pigweed after emergence, apparently because of root uptake after rains have incorporated the chemical into the soil. This is important in a year when rainfall following application has been insufficient to incorporate the chemical before weed emergence. Spartan weed control is limited in spectrum and duration, resulting in grass and broadleaf weed emergence that will likely require additional weed control practices. Poast or Select/Arrow /Prism can be applied for grass control, often along with bromoxynil + MCPA herbicide to provide complete weed control. The above scenario is similar with fall trifluralin. Trifluralin will give better broad spectrum weed control generally because of better grass control but is weaker on kochia than Spartan. Trifluralin is weak on volunteer grains and wild oat and has no control of resistant green foxtail. The result is usually the additional need for post emergence herbicide application to have acceptable weed control.

A total post emergence program in flax has limited herbicide choices but can be effective. A major dilemma is timing of the application(s). Flax is not competitive with weeds and because a mature flax canopy does not completely shade the ground, weeds germinating after application can reduce yields and cause harvest problems. Grass control is generally very good even on larger grasses so timing isn=t as critical for good control with the available grass herbicides but later application allows weeds to compete and may result in lower yields than an earlier application. When weed pressure is light, application on 3-4 leaf grasses is acceptable. Earlier application is preferred under intense weed pressure (more than 5 wild oat or volunteer grain plants per square foot) and will increase yield compared to a later application.

Broadleaf weed control is more problematic because the herbicides MCPA and bromoxynil applied alone or in combination perform best when applied to weeds smaller than one inch in height. Under intense broadleaf weed pressure, application to small weeds(less than one inch tall in two inch tall flax) will result in better control of emerged weeds, have less flax injury and enable better flax yield than a later application to taller weeds. However, weeds like wild buckwheat, kochia and redroot pigweed can germinate and emerge after an application to 2-3 inch tall flax resulting in harvest problems and reduced yields. Soil applied herbicides can help with this problem by preventing early weed emergence and allowing a later application of post herbicides.

Growers have asked about using split application to control early and late weeds. Research is limited on use of split applications. Research using from one half to three fourths of full label with each application has shown split application of bromoxynil plus MCPA to improve weed control. Increased flax injury usually occurs and may be a problem, although the limited research with splits shows good flax recovery and yields. Some labels like Bronate Advanced have a seasonal limit on amount applied where other labels like Bison and Bronate do not have limits. Check label language to be certain of limits. Application in later afternoon and evening, using reduced rates and increasing the time interval between splits will help reduce injury risk from split application. Labels generally prohibit application to flax that is blooming.

Curtail M is also labeled for flax. Curtail M will not adequately control kochia and may require a separate application for kochia control or the addition of bromoxynil at a 0.25 lb a.i. per acre to improve kochia control. Research in one study at Langdon showed kochia control improving from 41 percent to 79 percent with the addition of Bromoxynil. Use of Bromoxynil combinations are not necessary in combination with Curtail M as adequate MCPA is present in labeled rates of Curtail M.

A final weed control option to help with harvest involves the use of glyphosate or sodium chlorate to clean up escaped weeds at 70 -80 percent brown boll stage. Glyphosate should not be applied to flax intended for seed production as reduced seed germination is a possibility.