Amaranthus / chaulai (pigweed)
A fast-growing summer broadleaf weed that shoots up quickly, competes hard, and produces huge numbers of tiny long-lived seeds.
- Type
- Broadleaf weed (annual, summer)
- Life cycle
- Annual; huge long-lived seed
- Spreads by
- Seed (very prolific, tiny, long-lived)
- Main harm
- Fast competition with young crop; big seed bank
Overview
Amaranthus (chaulai, pigweed) is a group of fast-growing annual broadleaf weeds — including Amaranthus viridis and related species, and close relatives like Digera and Celosia — that are common in maize, cotton, sugarcane, groundnut and vegetables in the warm season. They have oval to lance-shaped leaves on an erect, often reddish-tinged stem, and dense green (sometimes reddish) spike-like flower/seed heads. Some, like chaulai, are also grown and eaten as a leafy vegetable, but in a crop they are aggressive weeds.
They germinate and shoot up very quickly with the crop and compete strongly for nitrogen, light, water and space, especially before the crop closes its canopy. Their biggest weedy trait is prolific seeding — a single plant produces huge numbers of tiny seeds that are long-lived in the soil and build a big seed bank. Management is about controlling them early, before they compete and seed: inter-cultivation, a competitive canopy-closing crop, mulch, and timely herbicides.
How to identify it
- Fast-growing annual broadleaf weeds with oval to lance-shaped leaves on an erect, often reddish-tinged stem.
- Dense green (sometimes reddish) spike-like flower/seed heads.
- Shoots up quickly with the crop, often taller than other broadleaf weeds early on.
- Common in warm-season crops — maize, cotton, sugarcane, groundnut, vegetables.
Why it is a problem
- Germinates and grows very fast, competing strongly with the young crop for nitrogen, light, water and space.
- A single plant produces huge numbers of tiny seeds that build a big, long-lived soil seed bank.
- Competes hardest before the crop closes its canopy, at the crucial early stage.
- Some species can also host pests/diseases and contaminate produce.
Cultural & preventive control
- Inter-cultivate/hoe early to remove pigweed while the crop is young, before it competes and seeds.
- Grow a competitive, well-fertilised, properly-spaced crop that closes the canopy quickly and shades it out.
- Mulch the inter-row to suppress germination, and use clean seed.
- Prevent seed set — with such prolific seeding, stopping seed is essential to run down the seed bank.
Herbicide control
- Use recommended pre-emergence herbicides (e.g. atrazine in maize, pendimethalin) and timely post-emergence broadleaf herbicides for the crop.
- Apply at the correct early stage and dose, when the weeds are small, and rotate herbicide groups.
- Combine herbicides with early inter-cultivation and a competitive crop for reliable control.
- Confirm the current herbicide, dose and timing for your crop with your local KVK.
Integrated management
- Combine early inter-cultivation, a competitive canopy-closing crop, mulch and timely herbicides.
- Prevent seed set every season to shrink the large seed bank over time.
- Focus on the early weeks, when pigweed competes hardest and is easiest to control.
Crops most at risk
Where this problem is called out in our crop guides — open a crop for the full package of practices.
Frequently asked questions
Which fast-growing reddish-stemmed broadleaf weed is shooting up in my maize/cotton?
A fast-growing broadleaf weed with oval to lance-shaped leaves on an erect, often reddish-tinged stem and dense spike-like green/reddish seed heads is Amaranthus (chaulai / pigweed). It competes strongly with the young crop and seeds prolifically. Control it early: inter-cultivate/hoe while the crop is young, grow a competitive canopy-closing crop, mulch, and use a recommended herbicide (e.g. atrazine in maize) at the right early stage — and prevent it setting seed.
Why is Amaranthus so hard to keep out year after year?
Because a single plant produces a huge number of tiny seeds that are long-lived in the soil, so even one season of escapes builds a large seed bank that keeps supplying new plants. The seeds germinate readily in the warm season. To reduce it over time you have to stop it setting seed — remove escapes before they seed — alongside clean seed, early inter-cultivation, a competitive crop and timely herbicides, which together gradually run the seed bank down.
Chaulai is a vegetable — should I still control it in my crop?
Yes. Although some Amaranthus (chaulai) is grown and eaten as a leafy vegetable, as a weed in maize, cotton or sugarcane it competes strongly with the crop for nitrogen and light and seeds prolifically, costing yield and building the seed bank. So even if you pick a little for the kitchen, do not let it grow freely in the crop — control it early with inter-cultivation, a competitive canopy and timely herbicides, and prevent it setting seed.
Symptoms and control measures follow ICAR, KVK and state agricultural-university package-of-practices; any named chemical is a registered use. Always read the product label and confirm the dose for your crop and zone. editorial policy.