Spiny amaranth, or spiny pigweed, (Amaranthus spinosus) is an annual pigweed species that’s critical to control as it has been linked to nitrate toxicity in livestock.
It has rough, erect stems and grows up to 6 feet tall. Leaves alternate and are a dull green. Its small green flowers are in dense spikes at stem tips and upper leaf axils. Each flower is surrounded by three shiny bracts. Its seeds are small, black and shiny.
Spiny amaranth is one of the more common amaranth species and can be found throughout the United States but is found mostly in the Southeast. It thrives in hot weather, tolerates drought and responds to high levels of available nutrients, which is why you often find it near feeding or other disturbed areas. Infestations often occur in pastures that have been heavily grazed or maintained with minimum inputs.
Controlling spiny amaranth can be especially difficult, because it can germinate almost any time of year. Controlling existing infestations is possible, but you may find a newly established patch, after controlling an existing patch, from a different seed source. Because of this, it’s important to use a good, residual herbicide to provide pre- and postemergence control. We recommend treating it with 12 to 16 fluid ounces of DuraCor® herbicide per acre. Use lower rates when weeds are small and actively growing. Increase rate as the season progresses and plants become more mature.
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