Paraquat for rice

RiceIn Asia alone, more than two billion people obtain over 60% of their calories from rice. It is the most rapidly growing source of food in Africa and is critical to food security. Long grain rices are typically of the indica race and include the fragrant Jasmine rice from Thailand and Basmati rice from India. Short grain rice, typically japonica, is usually more sticky than long grain and is favoured in Japan. Saki rice is grown in Japan to make rice wine, and in Indonesia there are red and black grained varieties. About 80% of the world's rice is grown by smallholders in these places. In Asia, women are often responsible for rice farming as men have moved to work in the cities. Efficient and productive rice-based production systems are essential for economic development and for improved quality of life for much of the world's population. Plant breeding, crop protection, water management and fertilization have increased productivity and reduced the costs of production. Weeds can reduce the yield and quality of rice by competing with the crop for light, nutrients and space; and their seeds can contaminate the harvested grain. Some of the most widespread and aggressive weeds are the Echinochloa species (barnyardgrass). Infestations of only ten of these weeds per square metre have been recorded to reduce yields by 25%. Also difficult to control is red rice which is the same species as commercial varieties. Cyperus rotundus is a sedge which has been called ‘the world’s worst weed’.

Rice fact file

  • 1 billion people have jobs associated with rice
  • 746 million tonnes were harvested in 2013
  • 85% of rice is grown in paddies
  • 4 crops per year can be grown in some areas
  • 2 main types of growing system: flooded (paddy) and dry (upland)
Using paraquat for weed control enables savings in time, cost and labor by reducing or eliminating the need for plowing in preparing fields for rice. As a broad spectrum herbicide, paraquat allowed the development of no-tillage (‘no-till’) systems. These systems do not rely on plow to control weeds. Not disturbing the soil helps prevent erosion and maintains a healthy soil. Recent work suggests that the production of methane (a greenhouse gas more damaging than carbon dioxide) from plant material decaying in anaerobic conditions after burial is significantly reduced under no-till. Controlling weeds can cost a lot of money, time and effort. Competitive weeds must not be permitted to set seed as this will contaminate the land for years to come. Apart from directly affecting the crop, weeds can block irrigation channels making water management difficult. Allowing weeds to grow unchecked in and around rice fields (ie on paddy bunds) can attract insect pests and rodents, and act as hosts for diseases. However, a managed vegetative cover is important to give structure and stability to the soil, helping to prevent erosion, and providing a habitat for Rice grains developing in paniclesbeneficial flora and fauna. Herbicides like paraquat and glyphosate have no residual activity in the soil and do not affect the rice crop. Glyphosate gives good control of perennial weeds

Description

Weeds that return year after year. Some die back in the winter but their roots remain alive and shoots reappear in spring; some don't die back and grow in size and stature the next season.

Authoritative On-line References and Resources

The International Weed Science Society represents individual associations around the world.
, but its intensive use can lead to adverse changes in the weed flora towards more aggressive broadleaved weeds

Description

The leaves are "broad" as opposed to the "narrow" leaves of grasses. Also called 'dicots' having two seed leaves, while grasses are 'monocots' having one seed leaf.

Authoritative On-line References and Resources

http://www.iwss.info The International Weed Science Society.
, and even cases of weed resistance

Description

The inherited ability of a plant/weed to survive a dose of a herbicide normally lethal to that species.

Authoritative On-line References and Resources

http://www.weedscience.org/in.asp The International Survey of Herbicide Resistant Weeds monitors the evolution of resistant species and assesses their impact. All confirmed instances of new cases are listed.
to glyphosate are arising. Paraquat can provide the alternative means of effective and sustainable weed control.