Water Lettuce in Rice Fields: How to Spot and Control Kiapo
Water lettuce is a floating broadleaf weed that farmers call kiapo or kiyapo. It forms small green rosettes on the water of irrigated lowland rice fields and canals. This page shows you how to spot it early, how much it can cut your palay yield, and how to clear it before it covers the water.
What Is Water Lettuce?
Water lettuce, or Pistia stratiotes, belongs to the aroid family, Araceae, the same family as gabi. Farmers know it as kiapo or kiyapo. It does not root in the soil. Instead, it floats on the water, with soft leaves in a rosette and fine roots hanging below. You find it in irrigated lowland rice fields, where water stays in the field and canals for long periods.
It is a perennial, so it keeps growing as long as there is water. It makes seeds, but its main way to multiply is through offshoots. Each mother plant sends out short runners called stolons, and a new small plant forms at the end. These young plants break off and drift with the water to new parts of the field.
| Name | Water lettuce |
|---|---|
| Scientific name | Pistia stratiotes |
| Family | Araceae |
| Weed group | Broadleaves (see the three groups) |
| Local names | Kiapo, kiyapo |
| Life cycle | Perennial |
| Spreads by | Seeds and vegetative offshoots connected stolons |
| Where it grows | Irrigated lowland rice fields |
How to Identify Water Lettuce
Look at the water surface between your rice hills. This weed floats in small rosettes that look like tiny heads of cabbage or lettuce. The leaves are thick, soft and yellowish green, with ridges running along them. Under the water, it carries feathery roots. Small daughter plants sit nearby, tied to the mother by short runners. It is a floating broadleaf with wide leaves, so it drifts on the water instead of rooting in the mud like grasses and sedges.
- Small floating rosettes on the water that look like little cabbage heads.
- Thick, soft, yellowish green leaves with ridges running from the base to the tip.
- Feathery roots hanging in the water under each floating plant.
- Young daughter plants joined to the mother plant by short runners.
- Thick floating mats in corners, drains and canals where the water slows down.
Why It Hurts Your Palay
Young plants do little harm. While the rosettes were still small, about 3 cm across, they had little or no effect on the grain yield of transplanted rice. Mature plants, about 10 cm across, are another story. Left to compete at the same density all season, they cut grain yield by 12 percent.
Large mats also cover the water and shade it. They clog canals and slow the flow of water into your field. So the longer you wait, the bigger the problem gets.
How to Control Water Lettuce
- Scoop out the plants with a net or a basket while they are still small, before their offshoots multiply across the field.
- Clean the canals and inlets too. Floating plants drift in with irrigation water, so a net or screen at the inlet helps stop them.
- Pile scooped plants on high ground far from water to dry out, and never throw them back into canals or drains.
- Check the field every week, because each missed plant can send out new daughter plants.
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 water lettuce 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 Water Lettuce 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.
- Plow and harrow well, and rake out the runners, roots or pieces you turn up. A small piece left in wet soil can grow a new plant.
- 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 Water Lettuce?
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 Water Lettuce
What is water lettuce called in Tagalog?
How do I get rid of water lettuce in my rice field?
How does kiapo spread so fast?
Get Water Lettuce out of your field
With Libre + Anee, read the whole guide: how to tell it from your crop, and what to do and spray at every age of your crop.
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