Integrated Pest Management
Redroot Pigweed
Amaranthus retroflexus
Redroot pigweed (Howard F. Schwartz, Colorado State University, Bugwood.org)
Redroot pigweed flowers (Joseph M. DiTomaso, Bugwood.org)
Description
- upright plant 1 – 6 feet tall with thick stems and a taproot
- lower stems are often reddish or red striped
- leaves are oval with a tapering point, occasionally tinted red
- densely clustered flowers appear on a spike at the tip of branches
- flowers are green with a pinkish tint
Location
- gardens, cropland and open spaces
Life Cycle
- summer annual; germinates primarily in summer, and anytime when soil moisture is sufficient
- plants produce tens of thousands of seeds that stay viable up to 10 years or more
IPM Recommendations
- Seed populations can be reduced by soil solarization.
- Competition for light from taller desired vegetation can help control weedy patches.
- Apply a mulch layer 3 inches deep on planting beds to reduce seed germination.
- Pre-emergent herbicides are not always effective since germination can take place year-round.
- Apply an appropriate post-emergent herbicide directly to target weeds.