Spiny amaranth

About

A pigweed armed with a pair of sharp spines where each leaf meets the stem, common in pastures, gardens and fields, especially in the Southeast. It makes enormous numbers of seeds, the spines hurt bare hands, and it can build up nitrates that sicken livestock.

Also called spiny pigweed, spiny carelessweed, stickerweed, hogweed

How to identify it

Look for

An upright to bushy plant 1-4 feet tall (sometimes 5) with smooth, hairless stems that are often red. Leaves are alternate and oval to egg-shaped, about 1-2.5 inches long. Look for two stiff spines, up to about 1/2 inch, at each leaf joint; male flowers form slender spikes at the tips and female flowers cluster along the stem.

Look-alikes

Other pigweeds, such as redroot, smooth and Palmer amaranth, have no spines at the leaf joints.

Where it grows

Overgrazed or bare spots in pastures (such as around hay feeders), gardens, crop fields and waste areas.

When

Seedlings come up in late spring and early summer and grow through the hot months; seeds sprout best in warm soil at or near the surface.

How it spreads

By seed; plants make roughly 110,000-235,000 seeds, most of which sprout from the soil surface.

Most common in

What to do, gentlest first

Start at the top. Weed killers are a last step; always read and follow the label.

1. Keep grass thick Prevent

   A dense, healthy lawn or pasture (right pH, enough fertility, no overgrazing) leaves little bare soil for it. Move hay feeders or other heavy-use spots around.

2. Hoe small plants, dig bigger ones before they flower By hand

   Hoe seedlings while they are under about an inch tall. Dig out larger plants with a spade or dandelion fork before flower spikes appear; mowed plants can still make some seed.

   Wear sturdy gloves; the spines are sharp.

3. Mulch thickly Barrier

   A 3-4 inch layer of straw or hay cuts pigweed emergence by about 90 percent.

4. Treat seedlings in lawns or pasture Conventional spray

   Dicamba or 2,4-D, applied while plants are small seedlings, controls it in grass areas.

   Read and follow the label. Many lawn weed killers also kill vegetables and flowers, and glyphosate harms any plant it touches.

Uses, wildlife and pets

Pets

Not listed by the ASPCA. It can store high levels of nitrate, and cattle, goats, sheep and pigs that eat it (usually only when other forage is short) risk nitrate poisoning and heart or kidney damage. The spines can also hurt animals.