– Clif Little, OSU Extension Guernsey County
Spiny amaranth (Amaranthus spinosus), or often referred to as spiny pigweed, is becoming common throughout Ohio. As the name suggests, this plant is armed with two very sharp spines at the base of the leaves at each node. This summer annual species is most often found in livestock feeding areas and corral areas within pastures but it will also occupy hay fields. This weed does well in bare, highly compacted areas where it has little competition. If not controlled, spiny amaranth spreads throughout pastures and hay fields.
Animals avoid grazing around this plant because of the sharp spines. Like all pigweeds, this plant is an abundant seed producer. Seeds form this plant can germinate throughout the summer.
Mowing does little to control this plant and if done at the incorrect phase of growth may spread seeds. Since spiny amaranth is often found in heavily grazed areas where soil is exposed, when implementing a control strategy we must change our management of this area to affect any long term solution.
The OSU Weed Control Guide, Bulletin 789, available from your local OSU Extension office list several herbicide options for pigweeds. Since this plant has a tremendous ability to reseed and germinate a residual herbicide should be considered. Before purchasing an herbicide be sure and review the entire product label for all restrictions unique to your forage management. Telar, Milestone, Crossbow, Forefront and GrazonNext HL are examples of a few products which have been shown to provide residual control of this weed. There are additional products that will work effectively on spiny amaranth and no product endorsement is implied.