Weed Management in Rice: The Whole Season Plan for Clean Palay

Control weeds from planting until the rice canopy closes. The usual steps cover the first 40 days, so weed management in rice is won or lost early.

Know your rice weeds first

Weeds in Tagalog are damo, but the word alone will not tell you how to kill one. Rice weeds fall into three groups that need different herbicides. Grasses have round, hollow, jointed stems. Sedges have solid, three sided stems, and broadleaves have wide leaves with a net of veins. Perennials such as purple nutsedge, or mutha, also regrow from tubers and creeping stems.

See our guide to the types of weeds, the common weeds in the Philippines with local names, and the full weed catalogue. If a plant puzzles you, photograph it and ask Anee, the smart farm technician in anee.io.

Weed management in rice starts with prevention

The cheapest weed never reaches your paddy. An old saying goes: one year of seeds, seven years of weeds. So keep each door shut.

• Clean seed. Pure, full and uniform seed carries no weed seed and gives 85 percent germination or better.
• A clean punlaan (seedbed). Weeds there ride to the field with the seedlings.
• Clean canals and bunds. Weeds on the pilapil drop seeds into the irrigation water.
• Clean tools and machines. Mud on a hand tractor or harvester carries weed seed from farm to farm.
• A clean fallow. Stop weeds from flowering after harvest, so fewer seeds wait in the soil.

Prepare the land to kill weeds

Good land preparation buries weeds, tears shoots from roots and makes dormant seeds sprout so you can kill them. It also drains the food stored in perennial weeds. Follow this sequence.

Use water as a weed control

Water is the best weed control, because most grasses and some sedges cannot sprout or grow under a flood. Keep about 2 to 5 cm of water in the field. If water allows, keep it flooded from transplanting until the canopy covers the soil. Still, wet land weeds such as gabi gabi thrive in flooded paddies, and dry land weeds take over rainfed fields that dry out.

Water also finishes a post emergence spray. Bring it back 1 to 3 days after spraying, 3 to 5 cm deep, and hold it for 4 to 5 days to keep the weeds under but the young rice above it.

Hand weeding and the rotary weeder

Hand weeding with a sickle or bolo is slow but thorough. Pull the whole plant or cut off the seed head before it ripens, so a weed that survived a spray leaves no seed. Start within two weeks of planting. Pile pulled weeds on the bund, since some survive in standing water.

A rotary weeder works faster but needs straight rows. It cuts, tramples and buries the weeds between them. Run it when weeds have three to four leaves, with 2 to 3 cm of water, then hand pull the weeds near the hills.

Biological control: let nature help

Biological control uses insects, microbes and plants to keep weeds below the level that cuts yield. It matters most in organic rice, where the rules ban synthetic pesticides.

• Azolla. This freshwater fern fixes nitrogen with blue green algae. It can cut weed growth by up to 80 percent in transplanted and direct seeded rice.
• The Altica beetle. This small black beetle eats the leaves of Ludwigia weeds, the kahoy kahoy of the paddies. Spare it from needless insecticide sprays.
• Two fungi. Alternaria alternata f.sp. sphenocleae blights gooseweed, and the rust Puccinia philippinensis attacks purple nutsedge.

Herbicides: the last tool, not the first

Careless herbicide use harms people, animals and water. Spraying one kind again and again, at the wrong dose or time, also breeds weeds it cannot kill. So spray only when prevention, water and weeding fall behind.

A pre plant spray hits weeds before you plant, never once rice is up. Pre emergence herbicides go on the soil before weeds come up, and post emergence ones hit weeds with leaves. Choices vary by region, so ask your local agricultural officer and read our guide to herbicides for rice weeds.

Weed control in rice by crop age

These steps go by days after planting, for lipat tanim and sabog tanim. Broadcast rice has no rows, so a rotary weeder does not fit it.

The direct seeded steps stop at day 30, so the last cell follows one rule: never let weeds set seed. After any post emergence spray, follow the water rule above. The weed control helper in anee.io lists the active ingredients for each window and weed group.

Let anee.io keep the weeding days

In anee.io, the cropping calendar dates every task from each lot's own day zero. So each weeding lands on the right day, even when you planted your lots a week apart. Anee also reads your weather, so you can ask if today suits a spray.

Weedy rice: prevention is the only cure

Weedy rice, or halo, lahok and sabag, is rice too. So no selective herbicide can kill it inside a rice crop. Prevention is the whole fight. Plant certified seed, clean the harvester before it enters your field, and pull off types early, before their grain drops. Each harrowing in land preparation also kills a flush of sprouted seed.

Herbicide resistance and barnyard grass

Some barnyard grass, or bayakibok, in direct seeded areas of the Philippines now resists butachlor and propanil. Resistance builds when one herbicide group goes on again and again, at the wrong dose or time, until only survivors seed the next crop.

Check the group number on each label and switch groups between seasons. For example, butachlor is group 15 and propanil group 5 in the HRAC numbering. Also pull any grass that survives a spray before it flowers.

Questions farmers ask about weeds in rice