Hedyotis diffusa: How to Spot and Control It in Rice Fields
Hedyotis diffusa, known in English as snake needle grass, is a slender broadleaf weed. It is not a grass, but it has thin leaves and tiny white to light purple flowers. It grows in rainfed lowland rice fields in the Philippines. This page shows you how to spot it among your palay and how it competes with the crop. Then it shows how to control it before it seeds.
What Is Hedyotis diffusa?
Hedyotis diffusa is a small annual herb in the coffee family, Rubiaceae. Its English name is snake needle grass, but do not let the name fool you. It is not a grass at all. Instead, it is a broadleaf weed and a cousin of the pisak plants. No Filipino local name is listed for it yet, so you may simply hear it called damo.
You will usually find it in rainfed lowland rice fields. This weed lives for one season. Within one crop it sprouts, grows, flowers, sets seed and dies. Seed is its only way to spread. The small seeds drop to the soil and wait there for the next planting. That is why a few plants this season can mean many more next season.
| Name | Hedyotis diffusa |
|---|---|
| English name | Snake needle grass |
| Family | Rubiaceae |
| Weed group | Broadleaves (see the three groups) |
| Local names | None recorded |
| Life cycle | Annual |
| Spreads by | Seeds |
| Where it grows | Rainfed lowland rice fields |
How to Identify Hedyotis diffusa
Look for a small herb with slender stems that branch out low among the rice. The leaves are thin and narrow, sometimes a bit wider, and they sit on the stem with little or no stalk. Its leaves look narrow, yet it is a broadleaf weed, not a grass or sedge. It has no leaf sheath, and the leaves grow in pairs. The tiny flowers are white to light purple, with four petals each.
- Slender, branching stems forming a small, loose plant among the rice hills.
- Thin, narrow leaves with no stalk or only a very short one.
- Leaves set in pairs on the stem, with no grass like sheath.
- Tiny flowers, white to light purple, each with four petals.
- Look alike tip: the name says grass, but its paired leaves and four petaled flowers mark a broadleaf.
Why It Hurts Your Palay
Small as it is, this weed still takes from your palay. It draws water and nutrients from the same soil as your rice. It also uses part of the fertilizer you apply. In rainfed fields, where water can run short, every drop it takes matters more. Young rice feels the competition most, before it can cover the ground.
Since it is an annual that spreads by seed, each plant that flowers adds to the seed supply in your soil. Next season, those seeds sprout with the new crop. Seeds can also get mixed into the harvested palay. Weedy patches give insects a hiding place near your rice as well.
How to Control Hedyotis diffusa
- Walk your rainfed field while the rice is young and pull these thin plants early. They are easy to miss among rice seedlings.
- Remove the plants before the small white to purple flowers turn to seed. Seeds that fall now sprout with your next crop.
- Hold rainwater in the paddy with well kept bunds when you can. Small seeded annual weeds sprout more easily on exposed soil than under water.
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 Hedyotis diffusa 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 Hedyotis diffusa 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 Hedyotis diffusa?
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 Hedyotis diffusa
What is Hedyotis diffusa commonly called?
How do I control snake needle grass in my rice field?
Will a herbicide for grasses kill snake needle grass?
Get Hedyotis diffusa 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.
The account is free, no credit card.
