Wrinkle grass (Ischaemum rugosum)
A rice grass weed that looks like young rice at first but has a twisted, wrinkled leaf — and in some areas no longer responds to the usual herbicide.
- Type
- Grassy weed (annual)
- Life cycle
- Annual, seed-propagated
- Spreads by
- Seed; carried in irrigation water and with rice seed
- Main harm
- Competes strongly with rice; some populations resist common herbicides
Overview
Wrinkle grass (Ischaemum rugosum) is a grassy weed of rice fields. When young, it looks a lot like rice seedlings or barnyard grass, which is why it is often missed during the first weeding. Its leaf blade has a twisted, wrinkled surface, and its leaf sheath (the part wrapping the stem) is hairy near the base with a purplish tinge. It grows thickest in wet, poorly drained, low-lying parts of a rice field.
It competes strongly with rice for nutrients, light and space, since it grows at a similar height and speed. In several rice-growing areas, some populations of this grass no longer die from herbicides that used to control them well, so spraying the same product every year can fail. Combining water management, land levelling and rotated herbicides works better than relying on one spray alone.
How to identify it
- Looks like young rice or barnyard grass at first glance, which is why it is often missed early.
- Leaf blade has a twisted, wrinkled (rough) surface — this is where the name "wrinkle grass" comes from.
- Leaf sheath (the part wrapping the stem) is hairy near the base, with a purplish tinge.
- Produces a flat, comb-like seed head with short bristly awns (hair-like points) when mature.
- Grows thickest in wet, poorly drained, low-lying parts of rice fields.
Why it is a problem
- Competes strongly with rice for nutrients, light and space, since it grows at a similar height and speed.
- Because it looks like rice or barnyard grass when young, it is often missed during early weeding.
- In several rice-growing tracts, some populations no longer die from herbicides that used to control them well, so relying on the same spray every year can fail.
- Heavy infestation lowers grain yield noticeably if left uncontrolled through the season.
Cultural & preventive control
- Level the field well and keep a shallow standing water layer (around 5 cm) after transplanting — this alone suppresses germination of many grassy weeds, including this one.
- Use healthy, weed-free seedlings and clean equipment to avoid carrying its seed between fields.
- In direct-seeded rice, good early water management matters even more, since there is no standing-water head start.
- Hand-remove any grass that looks slightly different from rice as soon as you notice it, rather than waiting.
Herbicide control
- A pre-emergence herbicide such as pretilachlor or butachlor, applied within 3 days of transplanting (or sowing in direct-seeded rice), checks the first flush.
- A post-emergence herbicide such as bispyribac-sodium controls many populations, but since resistance has been reported in some tracts, do not use the same herbicide group year after year.
- Rotate to a different herbicide mode of action periodically, and follow up with hand weeding on any survivors so they do not set seed.
- Ask your local KVK which herbicide is currently working well against this weed in your area, since resistance patterns differ by region.
Integrated management
- Combine good land levelling, water management, a pre-emergence herbicide, and a rotated post-emergence herbicide rather than depending on one spray.
- Never let survivors set seed — hand-pull or hand-cut any plant that escaped the spray before it flowers.
- Because this weed can resist herbicides, cultural control (water depth, clean seedlings, land levelling) matters more here than for most rice weeds.
Crops most at risk
Where this problem is called out in our crop guides — open a crop for the full package of practices.
Frequently asked questions
How do I tell this grass apart from young rice or barnyard grass?
Look closely at the leaf and stem base. Ischaemum rugosum (wrinkle grass) has a leaf blade with a twisted, rough, wrinkled surface, and its leaf sheath (the part wrapping the stem) is hairy near the base with a purplish tinge — young rice and barnyard grass do not have this wrinkled, hairy look. It grows fastest in wet, poorly drained, low-lying patches of the rice field.
Why doesn't my usual herbicide kill this grass anymore?
In several rice-growing areas, some wrinkle grass populations have stopped responding to herbicides that used to control them, especially when the same herbicide is sprayed year after year. If your usual spray is not working, ask your local KVK which herbicide currently works in your area, and avoid using the same one repeatedly — rotate between different herbicide types and combine spraying with water management and hand weeding.
What is the single most useful step against this weed?
Keeping a shallow layer of standing water (around 5 cm) in the field after transplanting suppresses germination of wrinkle grass and several other grassy weeds together, with no extra cost. Combine this with good land levelling, a pre-emergence herbicide, and hand-removal of any escapee that looks slightly different from rice, and do not rely on the same post-emergence herbicide every single year.
Symptoms and control measures follow ICAR, KVK and state agricultural-university package-of-practices; any named chemical is a registered use. Always read the product label and confirm the dose for your crop and zone. editorial policy.