Giant Salvinia in Rice Fields: How to Spot and Remove It
Giant salvinia is a hairy floating fern that covers the water of irrigated lowland rice fields with thick green mats. It spread into rice fields because farmers mistook it for azolla. This page shows you how to spot it, how to tell it from azolla, and how to clear it from your field and canals before it spreads.
What Is Giant Salvinia?
Giant salvinia, or Salvinia molesta, is a floating fern from the family Salviniaceae. It has no common local name, so it goes by its English name or simply salvinia. It floats on still or slow water. In the Philippines, it is a weed of irrigated lowland rice fields, where water stays in the field for most of the season.
It is a perennial and keeps growing as long as it has water. As a fern, it never flowers or makes seeds. Instead, it spreads mainly by broken pieces of stem, and it also forms spores. Moving water and farm tools carry these pieces to new spots. In fact, farmers brought it into rice fields by mistake, thinking it was azolla, the small fern they use as green manure.
| Name | Giant salvinia |
|---|---|
| Scientific name | Salvinia molesta |
| Family | Salviniaceae |
| Weed group | Broadleaves (see the three groups) |
| Local names | None recorded |
| Life cycle | Perennial |
| Spreads by | Cut fragments and spores |
| Where it grows | Irrigated lowland rice fields |
How to Identify Giant Salvinia
Look for a hairy, green mat floating on the water. This plant is a floating fern, not a flowering broadleaf, but its wide, round leaves set it apart from grasses and sedges. Young leaves lie flat and oval. Older leaves turn heart shaped and fold upward. Stiff, spine like hairs cover the top of each leaf. At each node, it carries two green floating leaves and one brown, root like leaf that hangs below.
- Thick, hairy green mats spreading across still water in the field and canals.
- Young leaves flat and oval, older leaves heart shaped and folded upward.
- Stiff, spine like hairs on the upper side of each leaf that shed water.
- Two green floating leaves and one brown, root like hanging leaf at each node.
- Look alike tip: azolla is much smaller, with tiny overlapping scales, and often turns reddish.
Why It Hurts Your Palay
Giant salvinia can reduce rice yield by 12.5 percent. It does this by covering the water with wide, thick mats. These mats block sunlight, crowd young rice and take nutrients from the water.
Mats also clog canals and drains, so water moves slowly into and out of your field. The worst part is how it got in. It spread into rice fields because farmers mistook it for azolla and moved it on purpose. So check every batch of azolla before you bring it to your field.
How to Control Giant Salvinia
- Scoop out mats with a net or basket while they are small. Leave no pieces behind, since each fragment can grow into a new plant.
- Check any azolla before you bring it in. Real azolla is tiny and scaly, while salvinia has bigger, hairy, folded leaves.
- Clean canals and inlets, and set a net or screen where water enters your field to catch drifting pieces.
- Pile removed plants on high, dry ground far from water so they dry out completely.
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 giant salvinia 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 Giant Salvinia 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 Giant Salvinia?
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 Giant Salvinia
What is giant salvinia commonly called?
How do I get rid of salvinia in my rice field?
How can I tell salvinia from azolla?
Get Giant Salvinia out of your field
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