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Cooperative Extension Fact Sheet FS1350

Redroot and Smooth Pigweed Life Cycle Disruptions for Effective Control in Specialty Crops

  • Meredith Melendez, Agriculture and Natural Resources Agent, Mercer County
  • Thierry Besancon, Extension Specialist in Weed Science, Plant Biology

Redroot (Amaranthus retroflexus) and smooth pigweed (Amaranthus hybridus) are annual broadleaf weeds commonly found in field and vegetable crops in New Jersey. Both species are very similar and are difficult to separate from each other in the field, especially at the seedling stage. Seeds of all pigweed species are easily transported across farms when moving soil or agricultural equipment, such as mowers or combines. Awareness of the life cycle and biology of pigweed are key to figuring out the best options for control in your fields.

Plant Description and Growth Habit

Both smooth and redroot pigweed have hairy stems in contrast with other pigweed species (Powell amaranth, Palmer amaranth, or waterhemp). Smooth pigweed can be differentiated from redroot pigweed when in bloom primarily from its many branched flower heads, and branches that are thinner and longer than redroot. Mature pigweeds have a short taproot, can reach up to six feet tall, and produce small green flowers in clusters that form in leaf stem joints and branch ends.

Zoom in Redroot pigweed seedling.
Fig. 1: Redroot pigweed seedling.
Zoom in Redroot pigweed axillary inflorescence.
Fig. 2: Redroot pigweed axillary inflorescence.
Zoom in Redroot pigweed leaves.
Fig. 3: Redroot pigweed leaves.

 

Zoom in Redroot pigweed plant.
Fig. 4: Redroot pigweed plant.
Zoom in Redroot pigweed pubescence.
Fig. 5: Redroot pigweed pubescence.
Zoom in Smooth vs redroot pigweed seedhead.
Fig. 6: Smooth vs redroot pigweed seedhead.

 

Management Strategies

Control of pigweed can be a multi-year process that involves several strategies for control. Organic and no-spray farming operations will need to rely on well-timed cultivation and strategic planting to compete with the weed infestation.

Pigweed Field Locations
Field Size of Population Suspected Introduction
Example: Field 4 Patchy throughout Equipment borrowed
     
     
     
     
     
     
     

Farm Decision Tool

Pigweed management is a multi-year process. Identifying existing pigweed populations on the farm and reflecting on your activities and how they impact these populations are the first steps to developing a management plan. Use the charts below to identify your pigweed populations and your current management methods, and develop a plan of action to eradicate pigweed from your production areas.

Zoom in Figure 7.

Figure 7. Seasonal decisions to make.

Field Current Strategies Timeframe
Field 4 Example: hand weeding Late summer
     
     
     
     
     
     
Field Potential Future Strategies Timeframe
Field 4 Clean equipment between fields Throughout 2022
     
     
     
     
     
     
     
     

References

  1. Grubinger, V. (2004). Flaming Stale Seedbeds for Weed Control.
  2. Lounsbury, N., Birthisel, S., Lilley, J., Maher, R. (2022). Tarping in the Northeast: A Guide for Small Farms (PDF). University of Maine.
  3. Mohler, C., Teasdale, J., DeTommaso, A. (2021). Manage Weeds on Your Farm: A Guide to Ecological Strategies. USDA Sustainable Agriculture.
  4. Mohler, C., Johnson, S. (2009). Crop Rotation on Organic Farms. USDA Sustainable Agriculture Research and Education.
  5. Uva, R., Neal, J., DiTomasso, J. (1997). Weeds of the Northeast. Cornell University Press.

September 2022