1. Introduction
Rice is cultivated in India in a very wide range of ecosystems. Weeds are a major impediment in rice production. Weeds compete with the crop for nutrients and water adversely affecting production, quality and quantity.
Adoption of proper weed management technologies can optimize rice production. Holistic multi-disciplinary integrated approach is necessary to manage weeds. Such a combination of various weed manaegement methods together is called integrated weed management (IWM).

2. Impact of Weeds
Weeds reduce yields by 12 to 98 %, depending on method of rice cultivation.
Threshold levels for a few weed species:
Species Economic Threshold Level
Cyperus iria / m2
Echinochloa crus-galli 20 / m2.
E. glabrescens / m2
Losses in grain yield due to infection of weeds:
Species Loss in Yield
Cyperus iria %
Echinochloa crus-galli 25 %.
E. glabrescens %

3. Integrated Weed Management (IWM)
IWM is aimed to reduce weed population to the level at which there would be no economical losses of crop. Weeds can be reduced by combination of appropriate weed management practices.
IWM is science-based decision-making process that uses environmental information, weed biology and ecology and all available technologies to control weeds while posing the least possible risk to man and environment.
Effective IWM combines preventive, cultural, mechanical and biological weed management methods in an effective, economical and ecologically safe manner.

4. Some Weed Species
Cyperus iria
Ischaemum rugosum
Leptochloa chinensis

5. Fimbristylis miliacea
Some Weed Species
Echinochloa colona
Eclipta prostrata
Fimbristylis miliacea
Sphenoclea zeylanica

6. Weed Control in Rice
Thorough land preparation month before planting destroys all existing weed seeds and vegetative parts of weeds. Weeds are allowed to emerge and are then killed during tillage operations.
First weeding should be done between 15 to 21 days after germination. Second weeding is done 30 to 45 days after first weeding. Hirsch – Manniella spinicaudata is a rice root nematode which controls many rice weeds
Application of mulch reduces weed growth and conserve moisture and fertilizers. Use of weed free seed material is recommended for better weed management.

7. Weed Management in Rice
Maintaining 5–7 cm water depth and avoiding drainage prevents germination of weed seeds. Azolla can suppress the weed growth by reducing sunlight and aeration.
Application of pendimethalin 1.0kg/ha on 5 days after sowing or Pretilachlor + Safener (Sofit) 0.45kg/ha on the day of receipt of soaking rain followed by one hand weeding on 30 to 35 days after sowing effectively controls weeds in kharif season.
Herbicide should be applied when there is a thin film of water in the field and then allow it to disappear. 

8. Advantages of Weed Control
Increase in yield and Purity of seed
maintained.
Conservation of soil moisture
through reduced competition for
sunlight, nutrients and water.
Reduced incidences of pest and disease
attack as weeds act as alternative hosts for them.
Hand weeding in Rice