Herbicide-resistant rice

  • About

  • Risks and benefits

  • Management and stewardship guidelines

  • Related items

rice field

Herbicide-resistant rice is a type of rice that is resistant to a particular herbicide or herbicides, which would otherwise damage the rice crop. These herbicides can be sprayed on the herbicide-resistant rice and they won’t affect the rice - they only kill weeds in the crop.

Herbicide-resistant rice was developed to help with weed control, particularly where rice is direct-seeded.

When rice is direct-seeded, seed is spread directly onto the field. In direct-seeded systems, rice competes with emerging weeds to get established. This is unlike transplanted rice seedlings which have a “head-start” on the weeds. Weeds are therefore more of a problem when rice is direct-seeded.

To control weeds, selective herbicides can be used in rice that affect the weeds, yet do not harm rice. Weedy rice and wild rices however are so closely related to “domestic rice” that these selective herbicides are not effective on them. This makes weedy and wild rice a more challenging problem to address. Herbicide-resistant rice can make weed management easier where unwanted weedy and wild rices infest rice fields.

Weedy rices are a serious problem in Malaysia, Vietnam, Sri Lanka, Thailand, and the Philippines. Heavy infestation with weedy rice may result in complete failure of rice crop. In addition, weedy rice reduces the value of the harvested rice crop by staining the grains an undesirable color.

As at April 2012, Clearfield® rice was the only herbicide-resistant rice available for farmers in some countries to grow. It was originally developed to help rice farmers in the US address a weedy rice called “red rice”.

Clearfield rice was first grown in the USA in 2002 and is now reported to be grown on more than 60% of the rice-growing area in the southern United States. It was released in Malaysia in 2010 and it may be introduced in other Asian countries in the coming years.

In addition to Clearfield rice, there are other types of herbicide-resistant rice including Liberty Link® and Roundup Ready® rice, but as at April 2012, they were not commercially available.

IRRI is not developing any herbicide-resistant rice varieties.

rice field

The use of herbicide-resistant rice can help improve control of weeds, including weedy and wild rices, and reduce weed control costs and the labor associated with manual removal of weeds.

However, without proper stewardship measures, weed problems are very likely to become more serious with the use of herbicide-resistant rice, especially in rice monoculture systems.

The risks of introducing herbicide-resistant rice include:

  • Herbicide-resistance can spread to the weedy and wild rices (via cross pollination), thus making their control more difficult.
  • Increased use of one herbicide type can facilitate the development of resistance to similar herbicides in a range of weeds, and thereby reduce the effectiveness of current herbicides for farmers.
  • Drift of herbicides from one field to another may damage adjacent crops.
  • Seeds of herbicide-resistant rice in the soil may turn into weeds in subsequent years when different rice varieties are grown.

farmer in rice field

Effective management strategies related to introducing herbicide-resistant rice include:

  • Do not grow herbicide-resistant rice in consecutive years in the same field.
  • Rotate herbicides and use of herbicide mixtures to ensure complete control of weeds.
  • Do not allow escaped weeds to go to seed by pulling out the escaped weeds.
  • Use integrated weed management programs that include effective cultural practices (land preparation, tillage practices, water management, etc.) and rotation of crop establishment methods.

In the USA, stewardship guidelines are recommended in conjunction with growing Clearfield rice. As herbicide-resistant rice gets released in Asia – where 90% of the world’s rice is grown – it is even more important stewardship guidelines are simultaneously adopted.

Joint efforts to develop stewardship guidelines

IRRI is currently calling on government and non-government organizations, research institutes, and the private sector to join forces to develop and implement good stewardship guidelines for herbicide-resistant rice in Asia.

Specifically, government institutes need to develop, regulate, and monitor guidelines on the use of herbicide-resistant rice in areas infested with weedy and wild rices and herbicide-resistant weeds. The private sector needs to take co-responsibility and assist in implementing stewardship guidelines.

IRRI also undertakes research into weed management in rice and our best practices are shared on the Rice Knowledge Bank.