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United States Department of Agriculture

Agricultural Research Service

Weed Physiology
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Weed Suppressive Rice Cultivars

• Weeds are the most costly pest of rice production

• Herbicides are applied to most rice fields each year to control weeds

• Weed-suppressive rice can reduce herbicide use and benefit the environment

• Weed suppression may be due to rice root growth, height and tillering, or natural herbicides produced by the rice roots (allelochemicals)




 Under low weed populations,

rice varieties show dramatic

differences in suppression.



Rice plots planted in barnyardgrass-infested field. Weed-suppressive rice varieties (two photos at right) dramatically reduce weed population and growth when plants are young. This suppression can continue through maturity.

Red Rice Outcrossing

  • Red rice is a Crop 'mimic' that reduces yield, and produces undesirable red seeds. Both are the species Oryza sativa.



Strawhull Red Rice  
Awned Red Rice  
  • Red rice can be controlled in herbicide-resistant rice ( Clearfield™ ) but outcrossing forms herbicide-resistant red rice hybrids.
Long-grain Rice
Medium-grain Red Rice
Rice X Red Rice Hybrid (medium-grain)





  Year 1: Rice (dark green) and red rice (light green) are grown together to allow plants to outcross as they would in a farm field.

  Year 2: Rice X awned blackhull red rice hybrids produce pink awns.   Year 2: Rice X awnless strawhull red rice hybrids flower very late (or not at all) and are awnless.


Year 2: Clearfield rice crosses at low rates with red rice. This produces small numbers of Herbicide-resistant hybrids that we confirm using DNA fingerprinting.
In this photo you can see remnants of the dead non-hybrids below the water's surface. These were killed with herbicide.

Research Support Staff:

Dr. David Gealy, USDA ARS, Research Plant Physiologist

Howard Black, USDA ARS, Plant Physiologist, Support Scientist

Bill Luebke, Biological Science Aid

Major Cooperators:

Nilda Burgos, University of Arkansas, Fayetteville

Karen Moldenhauer, University of Arkansas, Stuttgart

Merle Anders, University of Arkansas, Stuttgart

Brad Watkins, University of Arkansas, Stuttgart

Lew Ziska, USDA-ARS, Beltsville, MD

Mo Way, Texas A&M University, Beaumont



February-August, 2012, DBNRRC has hosted a visiting scientist from Egypt, Essam ElShamey for training in chemical separation techniques such as HPLC, and to investigate the effects of nutrient stress on release of weed-suppressive products (allelochemicals) from rice roots.

July 2012 - August 2013, we plan to host Carlos Nohatto at DBNRRC for a one-year project for training and research in rice weed physiology.  He is a Ph.D. student from the Federal University of Pelotas, RS, Brazil.

Last Modified: 9/26/2013
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