NEWS for North Dakotans
Agriculture Communication, North Dakota State
University
7 Morrill Hall, Fargo, ND 58105-5665
April 30, 1998
Weeds could cause serious problems in the many flax acres to be planted in North Dakota this year, according to Duane Berglund, agronomist for the North Dakota State University Extension Service. Flax does not shade the ground as much as cereal grains, so weeds have an excellent chance to develop—and some weeds, like wild buckwheat and red root pigweed, are luxury users of nitrogen that will rob flax of needed soil nutrients.
"Delayed seeding of flax, with tillage prior to seeding, will control wild oat and reduce infestations of other early germinating weeds," says Berglund. "But delayed seeding generally reduces flax yields.
"A preemergence herbicide will control weeds before emergence, minimize early weed competition and maximize flax yields. Post-emergence herbicides, applied to small weeds and flax soon after weed emergence, will usually give better control and allow more time for flax recovery from possible herbicide injury than applications to larger weeds and flax."
Berglund says that herbicides registered for use on flax include trifluralin, MCPA, Bromoxynil, Poast and sodium chlorate (Defol) as a preharvest desiccant. Here's how to use these herbicides on flax:
n Trifluralin at 1 to 2 pints per acre or 10 to 20 pounds of granules per acre must be fall-applied for foxtail and broadleaf weed control on fields to be planted to flax. Granular formulations may be applied to standing stubble; use liquid or granular formulations when residue will not interfere with incorporation. Seed flax less than 1.5 inches deep into a moist seedbed at 25 to 40 pounds of seed per acre. Recommendations call for lower rates in western North Dakota and higher rates in the eastern and northern regions of the state.
n Bromoxynil at 1 pint per acre on 2 to 8inch flax controls wild buckwheat, volunteer sunflower and most broadleaf weeds. Some flaxleaf burn may occur at higher rates or if high temperatures follow application. Mixtures of Bromoxynil plus MCPA may cause flax injury if applied during hot, humid conditions.
n MCPA at 0.5 pint per acre on 2 to 6inch flax controls many broadleaf weeds. MCPA amine rates higher than 0.5 pint per acre or MCPA ester should be used in flax for improved kochia and Russian thistle control.
n Poast at 10 to 30 fluid ounces per acre plus an oil additive will control annual and perennial grasses. It would be useful to control volunteer grains in flax. Poast plus oil is less effective if the grasses are under drought stress. Poast must be applied 75 days or more before flax harvest. Poast plus oil can be tank mixed with either Bromoxynil at 1 pint per acre alone or with MCPA ester at a 0.5 pint per acre rate. Some leaf burn, retarded growth and delayed maturity can occur with the tank mixes. Also, reduced grass control can result.
Berglund says 2,4D should not be used in flax—it's not labeled, and excessive injury will occur.
"Weeds not only compete with the growing flax crops to reduce yields, but also cause losses from dockage in flax seed shipments," Berglund notes.
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Source: Duane Berglund (701) 231-8135
Editor: Barry Brissman (701) 231-7866