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Prevent and Eliminate the Infestation of


What is weedy rice?

Weedy rice, also known as red rice, is a plant that belongs to the same genus and species as cultivated rice. In other words, it is a very close relative of cultivated rice. Because of this, the herbicides we use in rice do not kill it.

Why is weedy rice a problem?

Weedy rice is one of the most damaging weeds of rice worldwide. It can affect yield and quality significantly. Reports from the southern US show that yields can be reduced by 60%.

How extensive is the weedy rice problem in California?

California was practically free of weedy rice for the past 50 years but the weed has recently resurfaced. By 2021, over 3000 acres have been found infested.

What should I do if I suspect I have weedy rice in my field?

Follow the identification guidelines in this handout to rule out weedy rice.


The following are the weedy rice types indentified in California so far:

Click the images to learn more

Type 1

Type 2

Type 3

Type 4

Type 5

Type 6

Prevention and Management

Weedy rice (aka red rice) is a major problem in rice production in many parts of the world, and is found infesting over 3000 acres, as of 2021. Once weedy rice is established in a field, it is very difficult to eradicate since weedy rice plants cannot be controlled with rice herbicides. Furthermore, weedy rice seeds can survive for a long time in the soil, meaning that eradication measures become more difficult if plants are allowed to produce seed. Yield reductions in the southern US are as high as 60% in weedy rice infested fields. If weedy rice contaminates other rice during drying and storage, extra milling and sorting is required, which increases costs and may cause cracking and reduce milling yields.

Weedy Rice Identification Guidelines

Once all watergrass herbicide applications have been made, inspect surviving watergrass-like plants to rule out weedy rice. Check the collar to see if there is a ligule and auricle.

If ligule and auricle are absent, then the plant is watergrass.

If ligule and auricle are present, then the plant is rice or weedy rice.

If a plant looks suspicious, contact a UCCE Farm Advisor to confirm the identification. If the identification is positive, follow the best management practices developed by UCCE.

Guidelines to prevent infestations


All equipment coming into California from areas known to have weedy rice infestations must be thoroughly cleaned and inspected by the County Agricultural Commissioner.


Only use certified seed or seed produced in the Quality Assurance Program.

Guidelines to manage weedy rice in your field

During the Season

  • Before heading, rogue weedy
 rice plants from the field, or cut the plants at the base below
 the water line. If plants have
 headed,cut off the seed heads
 into a bucket or bag to prevent
 seed shattering.
  • Bagged seed heads should be disposed of in a landfill. Do
 not leave them by the side of the field.
  • Keep water on the field with 
no drainage until harvest.

At Harvest

  • Do not use a stripper
 header, as it tends to
 drop a lot of seed onto
 the soil surface.
  • Harvest infested fields last.
 Make sure you do not
 contaminate other fields
 by moving equipment
 from an affected field to a clean field.

Winter Management

  • If possible, burn straw 
in affected field. Straw
 should be cut as low as
 possible to the ground to
 facilitate burning.
  • Do not perform fall tillage
 as this may bury weedy
 rice seed.
  • Flood infested fields for as long as possible.

Long Term Management

  • Fallow infested basins or fields. Apply flush irrigation in the spring and summer to geminate weedy rice seeds. Use a burn down herbicide or tillage to kill emerged plants.
  • Crop rotation, if possible,
 allows for the use of herbicide modes of action which are not available in rice.

Sample Collection

To minimize the movement of weedy rice seed, plant material and contaminated soil, the University of California, in coordination with the California Rice Research Board and California Rice Commission, will be implementing the following weedy rice sample collection protocol, effective 2017.


1) Detain Transportation

Suspected weedy rice seed, plant material and soil should not be transported out of the possibly contaminated field.

2) Contact UCCE Rice Farming Systems Advisors:

If a suspected plant is found, contact one of the UCCE Rice Farming Systems Advisors:

Sacramento Valley:
Whitney Brim-DeForest (530-822-7515)
Luis Espino (530-635-6234)

San Joaquin Valley:
Michelle Leinfelder-Miles (209-953-6120)

The Advisor will visit the field, and if necessary, take a leaf or seed sample, depending on the timing and maturity of the plants. Growers and Pest Control Advisers do not have to be present in the field for collection.

3) Submitter Recieves Status

The status of the sample (whether or not it is weedy rice) will be given to the submitter as soon as identification is confirmed.


Luis Espino

UCCE Rice Advisor
Butte and Glenn
(530) 635-6234

Michelle Leinfelder-Miles

UCCE Farm Advisor
San Joaquin
(209) 953-6120

Whitney Brim-DeForest

UCCE Rice Advisor
Sutter, Yuba, Placer,
Sacramento, Butte
(530) 822-7515

© 2017 Regents of the University of California