- 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.
- 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.)
- Plants die after frost, seeds go dormant for the winter.
- 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:
- Cultivate at cotyledon stage or before 1’’
- Use dust mulch to deter additional pigweed germination
- Avoid recompacting soil
- 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.
- 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.
- Cover cropping with rye to release allelochemicals, suppressing pigweed.
- Stale seedbeds.
- Use of competitive cover cropping.
- 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