Rice is the staple food for more than half the world. In 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. Rice-based production systems and the operations processing the grain for food employ nearly one billion people in rural areas of developing countries. About 80% of the world's rice is grown by smallholders in these places. In Asia, women are often left to conduct many of the rice farming tasks 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. For thousands of years, cultivating rice has meant that people have had to work together, and the need for standing water in rice farming has shaped the landscape. Festivals are dedicated to rice and the crop was considered divine by many ancient Asian emperors and kings. Even today, the Japanese refer to rice as their ‘mother’ and regard rice farmers as the guardians of their culture and countryside. The UN Food and Agriculture Organisation declared 2004 as the International Year of Rice. There were nine themes running through the activities in the International Year of Rice: culture, nutrition, agro-biodiversityBefore the introduction of paraquat, weed control in rice depended on plowing to bury weeds. In some regions this is still the case and the several rounds of plowing needed, with intervals between them, are time consuming, costly and labor intensive. As a broad spectrum herbicide, paraquat allowed the development of no-tillage (‘no-till’) systems. These systems do not rely on plowing 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. Glyphosate is the main alternative non-selective herbicide, but its intensive use has caused new weed problems as species less well controlled have ‘shifted’ to become more dominant and troublesome. Some species have evolved biotypes which are resistant to glyphosate. Using paraquat as an alternative non-selective herbicide, with a different mode of action, in integrated weed management systems is helping to avoid problems of weed shifts
A vast number of insect pests can cause enormous damage to rice crops if not controlled. The general types are described here, but for further details visit the International Rice Research Institute (IRRI) webpages: Nematodes can also be significant pests. These includes species of Meloidogyne, Aphelenchoides and Ditylenchus
DescriptionThe variety of life in all its forms, levels and combinations. Includes ecosystem diversity, species diversity, and genetic diversity (IUCN, UNEP and WWF, 1991).
Authoritative On-line References and Resourceshttp://earthtrends.wri.org/ EarthTrends is a comprehensive online database, maintained by the World Resources Institute, that focuses on environmental, social, and economic trends. Statistics on biodiversity indicators are available., environment, livelihood, post-harvest processing, gender, science and economics. Science has provided improved technologies which enable farmers to grow more rice on limited land with less water, labor and inputs, thereby reducing damage to the environment. Improved plant breeding, weed and pest control, water management and fertilization increase productivity and reduce costs of production. Protecting rice from weeds, pests and diseases is essential to avoiding heavy losses in yield and quality of grain. Weed control is usually most important. Paraquat is a non-selective
DescriptionA chemical product used for eliminating all types of weeds (annual and perennial grasses and broadleaved weeds).
Authoritative On-line References and Resourceshttp://www.weeds.iastate.edu/ An invaluable source of contemporary information about herbicides and weeds from Iowa State University. herbicide which, by its use in integrated weed management
DescriptionA decision support system for crop protection which focuses on long-term prevention or suppression of pest problems with minimum impact on human health, the environment, and non-target organisms. IPM takes into consideration all available pest control techniques and tactics (cultural, mechanical, biological, chemical). IPM emphasizes the growth of healthy crops for better productivity with the least possible disruption to agroecosystems.
Authoritative On-line References and Resourceshttp://www.ipmcenters.org "The USDA's National Site for the Regional IPM Centers' Information System provides information about US commodities, pests and pest management practices, people and issues." systems, can provide solutions to these weed control issues.
Paraquat is an essential tool for rice farmersParaquat is used to prepare the land for cultivating rice and on the bunds (levies) which surround paddy fields to retain the flood water. Paraquat is a broad spectrum, non-selective herbicide because its mode of action is to inhibit photosynthesis. This process is essential to plants and means that paraquat destroys all green tissue. A video showing paraquat’s unsurpassed speed of action can be viewed here. However, paraquat is immobilised and deactivated on contact with the soil meaning that there are no leaching
DescriptionThe natural process by which water soluble substances are carried downward through the soil into groundwater. or root uptake problems to restrict its use. It can be sprayed to burndown weeds before planting a rice crop without risking damage to that crop or indeed subsequent crops in the rotation. You can read more about paraquat’s unique soil properties here.
CASE STUDY: Long-Term Paddy Rice Trials in JapanOfficially monitored long-term research in Japan has showed that paraquat does not enter crops and does not continually accumulate in the soil with repeated applications. The Japanese Association of PhytoRegulators (JAPR) oversaw field experiments with paraquat in Japan on three typical types of rice growing soil, lasting for up to 30 years. A normal rate of paraquat was applied every year to control weeds before planting rice and compared with traditional methods of mechanical weed control. After ten years the paraquat treatment in half of the treated area was stopped so that effects on soil residues could be monitored. No paraquat was taken up in to the rice crops and yields were the same regardless of weed control method. After paraquat application stopped, residues of the chemical in the soil declined significantly, showing that paraquat is degraded even under the anaerobic conditions in paddy soils for much of the growing season.
DescriptionA change in the weed community within a field i.e. relative abundance or type of weeds. This can be the result of a management practice like herbicide use or any other phenomenon that brings about a change in weed species composition. Species or biotypes adapted to current weed management practices increase, whereas weeds susceptible to those practices decrease.
Authoritative On-line References and Resourceshttp://www.weeds.iastate.edu/mgmt/qtr00-1/popdyn.htm A classic article on weed population dynamics on the Iowa State University Weed Science website. and resistance
DescriptionThe inherited ability of a plant/weed to survive a dose of a herbicide normally lethal to that species.
Authoritative On-line References and Resourceshttp://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.. The importance of paraquat in fighting weed resistance to glyphosate and maintaining farmers’ options to use conservation tillage
DescriptionAny tillage and planting system that covers 30 percent or more of the soil surface with crop residue after planting to reduce soil erosion by water.
Authoritative On-line References and ResourcesPurdue University-based Conservation Technology Information Centre. systems is discussed here. Further details of paraquat’s safety to the environment, spray operators and consumers can be found by referring to the Paraquat Fact Sheet. You can read more about the benefits of using paraquat here.
What is Rice?Rice is an annual grass typically growing 1-1.8 m tall. Shorter, higher yielding ‘semi-dwarf’ varieties were introduced during the ‘Green Revolution’ in the 1960s. The main species of cultivated rice is Oryza sativa. It is one of 23 species in the genus Oryza. Plants in this genus are tolerant to desert, hot, humid, flooded, dry and cool conditions, and grow in saline, alkaline and acidic soils. Oryza sativa originated in the humid tropics of Asia. One other member of the genus Oryza glaberrima, from West Africa, is the only other cultivated rice species. Asian rice has evolved into three eco-geographic races - indica, japonica and javanica. Within each of these races are distinctive varieties of rice which can be classified by their grain shape and texture. 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. ‘Golden Rice’ is a new type of variety being developed which is genetically modified to produce more beta carotene which is needed in the diet as a precursor to viatmin A. In some regions of SE Asia and Africa vitamin A deficiency is a serious problem, responsible for over a million deaths and half a million cases of blindness each year, particularly in children and pregnant women.
Where is Rice Grown?Rice is one of the world’s top three most widely grown crops. At 165 million ha harvested in 2013, it is third to wheat (218 million ha) and maize (184 million ha) in area. In terms of grain production, at 746 million tonnes it exeeds wheat (713 million tonnes) and follows only maize (1016 million tonnes). Rice is grown in warm, wet climates, or ones with rainy seasons, all around the world, but the vast majority is grown in Asia. India and China grow far more hectares of rice than any other countries. Areas under rice have been growing fastest in SE Asia. Some harvest data for main producing countries are shown below. The area of rice harvested in the world over the past decade has increased by 11%. However, global production in 2013 was 27% more than in 1999 as the average yield of rice over the world increased by 29%.
Table 1. Rice production in leading countries in 2013 (FAO data).
How is rice grown?The systems used for growing rice are perhaps more diverse than for any other crop. Some more sophisticated systems, such as in Japan where growing is technologically advanced, but on a small scale by part-time farmers, are quite complex. In more temperate areas, only one crop can be grown each year, being planted in the spring and harvested in early autumn. In tropical regions, two or more crops can be grown every year. For example, in the Mekong Delta in Vietnam, three crops are grown and in China four harvests have been gathered. Two main systems are based on whether the crop is submerged in a flooded field, or paddy, or grown like other cereals on dry land. The latter is often known as upland rice and confined to less developed regions, especially in Africa and Latin America. Paddy rice accounts for over 85% of the area grown and over 95% of rice production. Flooded rice depends on rain or irrigation. Soils are usually clays and often compacted to retain water. In some systems the soil is cultivated when wet, in others the fields are not flooded until the rice is well established. In Bangladesh, deep water rice is grown where the ears, or panicles, float on the top of stems which may be up to 5 m long. Rice is adapted to grow submerged by having a specialised tissue which allows air to reach the roots. Flooded rice is higher yielding because the crop transpires a lot of water in hot climates; because the pH of a flooded soil makes some mineral nutrients more available; and because many weeds are controlled by flooding. Aquatic weeds, however, can be problematic. Another key difference between growing systems is how the crop is established. In most of Asia, rice seedlings are transplanted in to paddies when they have two or three leaves. The transplants are raised from seed in nurseries. In larger scale systems, the crop is direct seeded by drilling as any other cereal into dry land before flooding; or seed, often pre-germinated, is scattered on to the flooded paddy. In California, for example, flooded fields are seeded by air. On smaller scales in the Eastern Hemisphere, preparing rice paddies is very labor intensive. Fields have to be cultivated to kill weeds and ensure the soil will allow water to percolate only slowly; the levies, or bunds, bordering the fields to retain the water have to be maintained; and the fields have to be irrigated and the rice transplanted. Often paddies are flooded and drained several times before a final draining before harvest. This is to manage the growth of the crop, eg to encourage tillering or discourage excessive stem elongation.
Protecting Rice CropsRice crops need protecting from weeds, pests and diseases to produce the best yields and quality of grain.
Insect pests of rice
- Defoliators lay eggs on rice leaves which are eaten by larvae when they hatch. Various flies (Diptera) and butterflies and moths (Lepidoptera) are defoliators. Later in development, adults and nymphs of beetles (Coleoptera) and thrips (Thysanoptera) feed on leaves. Grasshoppers (Orthoptera) can also be a problem.
- Sap feeders have needle-like mouth parts which they use to suck sap from rice shoots. Leafhoppers and planthoppers (Hemiptera) are widespread pests.
- Stem borers are the destructive larvae of otherwise harmless butterflies and moths. They burrow in stems causing ‘dead heart’ symptoms in younger shoots and ‘whiteheads’ in older plants in which the ears have failed to fill with grain.
- Root feeders live in the soil and include crickets (Orthoptera) and beetles.