Pigweeds & Palmer Amaranth: How to Identify and Control It
Amaranthus spp. (incl. A. palmeri) · Summer annual broadleaf
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How to identify pigweeds & palmer amaranth
- Oval to diamond-shaped leaves on an upright, branching stem
- Redroot pigweed: hairy stems and a pink-red taproot
- Palmer amaranth: smooth stems, long leaf stalks (often longer than the leaf), and very long seed spikes
- Dense, bristly flower spikes from summer on
Why it shows up
Pigweeds thrive in hot, fertile, disturbed soil. Palmer amaranth grows extremely fast, makes huge seed numbers, and many populations resist several herbicide groups, so it's a serious farm weed spreading from the South and Plains into the Midwest and Northeast.
Where it's a problem
- Southeast (zones 7–10) — Palmer amaranth is a top cotton and soybean weed across the Southeast.
- Midwest (zones 4–7) — Palmer amaranth has been spreading north in contaminated seed, feed and equipment; several Midwestern states ask growers to report new finds.
- Great Plains & Texas (zones 3–9) — Palmer and waterhemp are major Plains crop weeds; resistance to several herbicide groups is widespread.
- Southwest & Mountain (zones 4–10)
Control methods
1. Cultural (prevention)
- Mulch gardens and keep soil covered
- Never let plants go to seed
- Clean tools, mowers and equipment moving between fields
2. Mechanical
- Pull or hoe while small (under 4 in.)
- Bag and remove plants with seed heads
3. Organic options
- Mulches, cover crops, and hand-weeding before seed set
4. Chemical options
Herbicide safety — always follow the label. The label is the law: use only products labeled for your site, turfgrass or crop, and follow rates, timing, weather limits and protective equipment directions exactly. Keep people and pets off treated areas as directed, and check state and local rules. Active ingredients named here are examples from extension guidance, not endorsements; availability varies by state.
- Pre-emergents labeled for the crop or site
- Herbicide resistance is common in Palmer amaranth — on farms, follow your state extension's resistance-management program. Suspected Palmer amaranth in a new area should be reported to your county extension office
When to treat pigweeds & palmer amaranth by USDA zone
| USDA zone | Typical timing (from NOAA frost-date medians) |
|---|---|
| Zone 3 | Pre-emergent around Apr 19–May 3 (2–4 weeks before the typical last frost, May 17); spot-treat or pull escapes in early summer |
| Zone 4 | Pre-emergent around Apr 12–Apr 26 (2–4 weeks before the typical last frost, May 10); spot-treat or pull escapes in early summer |
| Zone 5 | Pre-emergent around Apr 5–Apr 19 (2–4 weeks before the typical last frost, May 3); spot-treat or pull escapes in early summer |
| Zone 6 | Pre-emergent around Mar 29–Apr 12 (2–4 weeks before the typical last frost, Apr 26); spot-treat or pull escapes in early summer |
| Zone 7 | Pre-emergent around Mar 14–Mar 28 (2–4 weeks before the typical last frost, Apr 11); spot-treat or pull escapes in early summer |
| Zone 8 | Pre-emergent around Feb 24–Mar 10 (2–4 weeks before the typical last frost, Mar 24); spot-treat or pull escapes in early summer |
| Zone 9 | Pre-emergent around Jan 26–Feb 9 (2–4 weeks before the typical last frost, Feb 23); spot-treat or pull escapes in early summer |
Zones 10–11 (frost rare): follow germination flushes after rains; pre-emergents in late summer/fall for winter weeds and late winter for summer weeds. Find your exact frost dates with the ZIP planner. Soil temperature and the product label take priority over the calendar.
Frequently asked questions
How do I get rid of pigweeds & palmer amaranth naturally?
Start with cultural and mechanical controls: Mulch gardens and keep soil covered; Never let plants go to seed; Clean tools, mowers and equipment moving between fields; Pull or hoe while small (under 4 in.); Bag and remove plants with seed heads.
What does pigweeds & palmer amaranth look like?
Oval to diamond-shaped leaves on an upright, branching stem; Redroot pigweed: hairy stems and a pink-red taproot; Palmer amaranth: smooth stems, long leaf stalks (often longer than the leaf), and very long seed spikes; Dense, bristly flower spikes from summer on.
When is the best time to treat pigweeds & palmer amaranth?
Prevent it with a pre-emergent applied 2–4 weeks before your average last spring frost, when soil reaches about 55°F.
Where is pigweeds & palmer amaranth a problem in the US?
Pigweeds & Palmer Amaranth is common in: Southeast, Midwest, Great Plains & Texas, Southwest & Mountain.
Sources & further reading
- NC State Extension Gardener Plant Toolbox: Amaranthus palmeri
- UC IPM (University of California) weed gallery: weed photo gallery
- Steppig et al. (2025). Common target-site resistance mutations for PPO-inhibiting herbicides in waterhemp ( Amaranthus tuberculatus ) and Palmer amaranth ( Amaranthus palmeri ) do not confer cross-resistance to trifludimoxazin. Weed Science. doi:10.1017/wsc.2024.103
- Herbicide examples are typical active ingredients named in university extension guides; products and registrations vary by state. See your state Cooperative Extension weed-control guide.
Related weeds in the same regions
Crabgrass · Dandelion · White Clover · Field Bindweed · Yellow Nutsedge · Common Chickweed · Broadleaf Plantain · Creeping Charlie (Ground Ivy) · All 27 weeds
Planning a garden? See planting calendars by state & zone.