pigweedBiological information:

  • Common name: Pigweed
  • Scientific name: Amaranthus retroflexus
  • Family or class: Amaranthaceae

Symptoms and/or signs to watch out for:

  • Rapidly over topping shorter crops.
  • Increasing stem growth and deploying leaves.
  • Tall, erect to bushy plants with simple oval to diamond shaped alternate leaves with small greenish flowers.

Life cycle:

  • Emerges after spring frost date.
  • Grows rapidly.
  • Competes vigorously with cash crops.
  • Reproduces by seed.
  • Dies with fall frost.
  • Seeds become dormant .
  • Have multiple dormancy mechanisms to germinate at different times the next year.

Mode of reproduction:

  • Reproduces asexually by seed.
  • Seeds are spread primarily by wind.

Vectors for the pest:

  • Pest Nematodes (meloidogynes spp.)

Overwintering habit:

  • Plants die after frost, seeds go dormant for the winter.

Alternate hosts:

  • Many crop pathogens including fungi
    • early blight in tomatoes and potatoes
    • lettuce drop
    • southern blight
  • Viral pathogens
    • cucumber mosaic virus
    • tomato spoiled wilt virus

Horticultural production information:

Preventative strategies:

  • Cultivate at cotyledon stage or before 1’’
  • Use dust mulch to deter additional pigweed germination
  • Avoid recompacting soil

Threshold levels:

  • There is no threshold level for pigweed because it is so highly prolific.
  • One female plant can produce 150,000 seeds per year.
  • If 99% percent were killed, 150 still survive cause the same problem.

Control options:

Physical controls:

  • Removing weeds in early fall can reduce pigweed seed rain.
  • Mulch – 3-4’’ straw/hay or black plastic after cultivation.
  • Use of in row drip irrigation directly on crop.

Biological controls:

  • Cover cropping with rye to release allelochemicals, suppressing pigweed.
  • Stale seedbeds.
  • Use of competitive cover cropping.

Chemical controls:

  • Most pre-emergence herbicides for broadleaved weeds.
  • Post-emergence application of: 2,4-D, dicamba, mecoprop, bromcynil, or atrazine.

Historical notes from Farm to YoU NH:

Date/circumstances observed (Pictures)

Control method used, efficacy of control method

  • manual removal (broadfork, by hand)
  • works effectively on small scale




Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s