Spiny Amaranth: How to Spot and Control It in Rice Fields
Spiny amaranth is a broadleaf weed with sharp spines that grows in rainfed lowland rice fields across the Philippines. One plant can make a huge amount of seed, and it also hosts a nematode that harms rice roots. This page shows how to spot it, why it matters to your palay, and how to remove it safely.
What Is Spiny Amaranth?
This damo belongs to the amaranth family, and farmers know it by many local names. Depending on the region, people call it alayon, ayang lalaki, ayantoto, baoan, bayambang, harum, gitingiting, kalitis, kalunai, kuanton, kudiapa, kulitis, taikada or uray. Spiny amaranth grows in rainfed lowland rice fields, where the soil stays dry for part of the season.
As an annual, it lives through one season and then dies. But it leaves plenty behind, because it spreads by seed and one plant can drop more than a hundred thousand of them. The seeds come tiny, round and shiny black, so you hardly notice them on the soil. They wait there until the field dries out enough for them to sprout.
| Name | Spiny amaranth |
|---|---|
| Scientific name | Amaranthus spinosus |
| Family | Amaranthaceae |
| Weed group | Broadleaves (see the three groups) |
| Local names | Alayon, ayang lalaki, ayantoto, baoan, bayambang, harum, gitingiting, kalitis, kalunai, kuanton, kudiapa, kulitis, taikada, uray |
| Life cycle | Annual |
| Spreads by | Seeds |
| Where it grows | Rainfed lowland rice fields |
How to Identify Spiny Amaranth
Run your eye along the stem before you touch it. This weed has branched, pale green stems with a pair of thin, sharp spines where each leaf and branch joins the stem. The leaves grow one at a time, oval to broadly lance shaped, and narrow down into a leaf stalk at the base. As a broadleaf weed, it has wide leaves with netted veins. At the tips and in the leaf angles, look for packed spikes of small green flowers.
- Pairs of thin, sharp spines where the leaves and branches meet the stem.
- Pale green, branched stems that prick your hands when you grab them carelessly.
- Simple oval to broadly lance shaped leaves, set one at a time along the stem.
- Leaf blades that narrow down into a clear leaf stalk at the base.
- Dense spikes and clusters of tiny green flowers at the tips and leaf angles.
- Look alike tip: slender amaranth looks similar but has no spines, so check the leaf joints.
Why It Hurts Your Palay
Spiny amaranth is a C4 weed. That means it uses strong sun and heat very well, so it can grow fast in open, dry patches of the field. Each plant can produce 117,000 seeds, which is why a few plants today can turn into a thick stand next season. So far, researchers have not reported how strongly it competes with rice for yield.
The bigger hidden danger lies underground. This weed is another plant that Meloidogyne graminicola, the rice root knot nematode, can live on. These tiny worms cause galls, or swellings, on rice roots. When this weed grows in or around the field, the nematodes can live on it even while no rice stands in the paddy.
How to Control Spiny Amaranth
- Always wear thick gloves when you pull it. Grip the stem low, below the spines, and pull out the whole root.
- Remove plants before the flower spikes ripen. One plant can drop 117,000 seeds, so even a few missed plants restock the soil.
- Clear it from levees and fallow fields too, since it can keep the rice root knot nematode alive between crops.
- Do not leave pulled plants with ripe spikes on the levee. Pile them away from the field where seeds cannot fall back into the paddy.
What to Do at Each Age of Your Rice
- 0 to 5 days: keep the soil saturated. Use a pre emergence herbicide only if the field had many weeds last season.
- 6 to 10 days: hand weed in transplanted rice. In direct seeded rice, this is the window for an early post emergence spray.
- 11 to 20 days: keep water in the field, weed by hand or with a rotary weeder, and let Azolla and the Altica beetle help. Spray only if those fail.
- 21 to 30 days: top up the water and keep weeding. Spray only if weeding fails.
- 31 to 40 days (transplanted rice): hand weed. A spray this late is only a rescue.
- After any post emergence spray, bring the water back within 1 to 3 days at 3 to 5 cm and hold it for 4 to 5 days. Keep young rice above it.
Active Ingredients That Work on Broadleaves
If water and weeding cannot hold spiny amaranth down, choose an active ingredient that works on broadleaves at the age of your rice. Each active ingredient in it is in a herbicide registered in the Philippines for rice. Shop by the ingredient on the label, never by the brand. If your field also has other kinds of weeds, the weed control helper in anee.io finds the ingredients that cover all of them.
| Rice age (days after planting) | Transplanted rice (lipat tanim) | Direct seeded rice (sabog tanim) |
|---|---|---|
| 0 to 5 days | Pretilachlor, Oxadiazon, Butachlor plus 2,4 D IBE, Pyrazosulfuron ethyl plus pretilachlor, Imazosulfuron, Penoxsulam plus butachlor, Tefuryltrione plus triafamone, Thiobencarb plus 2,4 D IBE | Pretilachlor, Oxadiazon, Pretilachlor plus butachlor, Butachlor plus 2,4 D IBE, Pendimethalin, Pyrazosulfuron ethyl plus pretilachlor, Butachlor with safener |
| 6 to 10 days | Butachlor plus propanil, Cyhalofop butyl plus bispyribac sodium, Bispyribac sodium, Penoxsulam plus cyhalofop butyl, Pendimethalin, Cyhalofop butyl plus propanil, Imazosulfuron, Propyrisulfuron, Clomazone plus propanil, Thiobencarb plus propanil, Flucetosulfuron, Cyhalofop butyl plus florpyrauxifen benzyl | Butachlor plus propanil, Cyhalofop butyl plus bispyribac sodium, Bispyribac sodium, Pyribenzoxim plus cyhalofop butyl, Penoxsulam plus cyhalofop butyl, Cyhalofop butyl plus propanil, Pyrazosulfuron ethyl plus pretilachlor, Pendimethalin, Propyrisulfuron, Clomazone plus propanil, Thiobencarb plus propanil, Pretilachlor plus pyribenzoxim, Penoxsulam, Flucetosulfuron, Cyhalofop butyl plus florpyrauxifen benzyl |
| 11 to 20 days | Cyhalofop butyl plus bispyribac sodium, Bispyribac sodium, Pyribenzoxim plus cyhalofop butyl, Penoxsulam plus cyhalofop butyl, Metamifop plus bispyribac sodium, Bentazone, Cyhalofop butyl plus ethoxysulfuron, Propyrisulfuron, Fenoxaprop P ethyl plus ethoxysulfuron, Flucetosulfuron, Carfentrazone ethyl, Florpyrauxifen benzyl, Cyhalofop butyl plus florpyrauxifen benzyl | Cyhalofop butyl plus bispyribac sodium, Bispyribac sodium, Pyribenzoxim plus cyhalofop butyl, Penoxsulam plus cyhalofop butyl, Metamifop plus bispyribac sodium, Bentazone, Pyribenzoxim, Cyhalofop butyl plus ethoxysulfuron, Propyrisulfuron, Fenoxaprop P ethyl plus ethoxysulfuron, Flucetosulfuron, Carfentrazone ethyl, Florpyrauxifen benzyl, Cyhalofop butyl plus florpyrauxifen benzyl |
| 21 to 30 days | 2,4 D amine, 2,4 D IBE, MCPA, Metamifop plus bispyribac sodium, Bentazone, Metsulfuron methyl plus chlorimuron ethyl, Fenoxaprop P ethyl plus ethoxysulfuron, Carfentrazone ethyl | 2,4 D amine, 2,4 D IBE, Cyhalofop butyl plus bispyribac sodium, Pyribenzoxim plus cyhalofop butyl, MCPA, Metamifop plus bispyribac sodium, Bentazone, Metsulfuron methyl plus chlorimuron ethyl, Pyribenzoxim, Carfentrazone ethyl |
| 31 to 40 days | Metsulfuron methyl plus chlorimuron ethyl | Not listed for direct seeded rice |
Spray Safely
Use only herbicides registered with the Fertilizer and Pesticide Authority, and follow the label on the pack: the rate, the timing, the water and the protective clothing. Switch herbicide groups between seasons so the weeds do not learn to survive them. Our guide to herbicides for rice explains the groups.
Keep Spiny Amaranth Out Next Season
- Plant clean, certified seed. Weed seeds mixed into the punla are the easiest way in.
- Keep the seedbed, the canals and the bunds free of weeds, so seed does not wash or blow into the paddy.
- Prepare the land well: flood, plow, let the weed seeds sprout, then kill them when you harrow. Level the field so water covers it evenly.
- Pull escapes before they flower and set seed, and carry them out of the paddy instead of leaving them on the bund.
- Keep the field clean after harvest and through the fallow, so fewer seeds build up in the soil for next season.
These steps work for every broadleaf weed in the paddy, not only this one. The weed management guide puts them in order for a whole season.
Not Sure It Is Spiny Amaranth?
Take a clear photo of the leaf, the stem and the flower or seed head, then ask Anee, the smart farm technician in anee.io, in Tagalog or English. Anee tells you which weed it most likely is, its group, and what to do at the age of your rice. You can also put the weeding days on your cropping calendar, so the team knows when to go in.
anee.io keeps your weeding, spraying and water on one calendar, and Anee answers when a plant looks wrong.
- Weeding days on the season calendar
- Photos and notes for every lot
- Anee, the smart farm technician, in Tagalog or English
Questions Farmers Ask About Spiny Amaranth
What is spiny amaranth called in Tagalog?
How do I control it in my rice field?
Is this weed harmful to rice besides the spines?
Get Spiny Amaranth out of your field
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