In the US, average sugar consumption is currently twice the maximum of 10% of daily calories recommended by the World Health Organization. However, as sugarcane is grown in 102 countries, and for a dozen of these it accounts for 25% of their cropland, its cultivation and processing provides livelihoods for tens of millions, and its export supports many national economies.
About 70% of all sugar comes from sugarcane, the rest from sugar beet. These crops grow in tropical to sub-tropical and temperate zones, respectively.
Significant environmental issues surround sugarcane. On the one hand, sugarcane is the biofuelDescription Fuel derived from biomass. Authoritative On-line References and Resources http://www.biofuelstp.eu/ The European Biofuels Technology Platform is upportd by the European Commission and aims to help develop cost-competitive, world class biofuel technology, contribute to the creation of a European biofuels industry and to identify the research needed to achieve this. feedstock which gives the best net energy gain and has the lowest carbon footprint. In Brazil, where bioethanolDescription Bioethanol is ethanol of biological origin. Crops containing sugar or starch grown for energy use include sugar beet, sugar cane, maize and wheat. "2nd generation" bioethanol will be made from cellulose from, e.g. waste straw and stover, willow and popular trees, sawdust, reed canary grass, switchgrass, Miscanthus. Authoritative On-line References and Resources http://www.eere.energy.gov/afdc/fuels/ethanol.html The US Department of Energy's Office of Energy Efficiency and Renewable Energy has am Alternative Fuels and Advanced Vehicles Data Center containing key information on all biofuels. has been made from sugarcane on a large scale since the oil crisis of the early 1970s, 55% of the crop is now used for this purpose. On the other hand, WWF considers that major environmental issues in sugarcane production include effluents; loss of habitats as land is cleared for cropping; and the consequences of various agronomic practices, especially:
- Soil erosionDescription Displacement of solids (soil, mud, rock and other particles) usually by the agents of currents such as, wind, water, or ice by downward or down-slope movement. Authoritative On-line References and Resources http://soilerosion.net/ This site brings together reliable information on soil erosion from a wide range of disciplines and sources. It aims to be the definitive internet source for those wishing to find out more about soil loss and soil conservation.
- Water contamination by run-offDescription The occurrence of surplus liquid (like rain) which originates up-slope and is collected beyond the ability of the soil to absorb it. The surplus liquid then flows away over the surface to reach the nearest surface water (pond, lake, river). Authoritative On-line References and Resources US Geological Survey's Water Science School and leachingDescription The natural process by which water soluble substances are carried downward through the soil into groundwater. of agrochemicals
- ResistanceDescription 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. arising in weeds, pests and diseases
Paraquat is a non-selectiveDescription A chemical product used for eliminating all types of weeds (annual and perennial grasses and broadleaved weeds). Authoritative On-line References and Resources http://www.weeds.iastate.edu/ An invaluable source of contemporary information about herbicides and weeds from Iowa State University. herbicide which when used to control weeds in conjunction with other practices can help mitigate these threats.
Paraquat is an essential tool for sugarcane farmers
Paraquat disrupts photosynthesis and quickly destroys all green tissue.
A video showing paraquat’s unsurpassed speed of action can be viewed here.
Weed control is unaffected even if rain falls 15-30 minutes after spraying. As such, it has been essential to the development of cultivation systems like no-tillDescription
Also known as conservation tillage or zero tillage is a way of growing crops from year to year without disturbing the soil through tillage ie cultivating the soil usually with tractor-drawn implements.
Authoritative On-line References and Resources
No-till.com: A portal for on-line information about no-till farming. which do not rely on plowing for weed control. The less the soil is disturbed, the more erosion is avoided.
Paraquat is deactivated immediately on contact with the soil. There are no run-off, leaching, persistence or root uptake problems to restrict its use. Unlike many other herbicides which have ‘residual’ properties it can be sprayed to burndown weeds before planting without risking damage to the crop.
You can read more about paraquat’s unique soil properties here.
Paraquat has a very robust environmental profile. Details of paraquat’s safety to the environment, spray operators and consumers can be found by referring to the Paraquat Fact Sheet.
Paraquat is not systemic like the alternative non-selective herbicide glyphosate so it can be applied up to the four leaf stage of sugarcane without lasting damage. In some situations the temporary scorching of the crop is even beneficial and stimulates the growth of side-shoots (tillers). Later, paraquat can be used to desiccate the crop by spraying by air 3-14 days before harvest.
Intensive use of glyphosate 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. Paraquat has a different mode of action, so when used in integrated weed managementDescription A 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 Resources http://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, helps to avoid problems of weed shiftsDescription A 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 Resources http://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.
The importance of paraquat in fighting weed resistance to glyphosate and maintaining farmers’ options to use conservation tillageDescription Any 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 Resources Purdue University-based Conservation Technology Information Centre. systems is discussed here.
You can read more about the benefits of using paraquat here.
What is sugarcane?
Sugarcane is a grass with a thick fibrous stem, growing up to 6m tall. Commercial varieties of sugarcane are complex hybrids of several species within the genus Saccharum. The best known species is Saccharum officinarum.
Sugarcane plants store sucrose in the stem sap to fill seeds after flowering. However, it is important that sugarcane crops do not flower if they are to give high sugar yields. At harvest, cane contains about 10% sugar, varying with variety, season and location.
Extracting crystalline sugar involves milling freshly harvested cane to produce raw sugar and then purifying this to make refined white sugar which is 99% sucrose.
In milling, cane is washed, chopped and shredded, then repeatedly mixed with water and crushed through rollers. The juice collected (‘garapa’) contains up to 15% sucrose, while the remaining fibrous solids (‘bagasse’) are a useful energy source, animal feed or used in paper making. Adding lime neutralises the cane juice pH. This stops sucrose breaking down in to glucose and fructose, and precipitates some impurities. Suspended solids are allowed to settle before the juice is evaporated to make a syrup. The syrup is concentrated under vacuum and sugar crystallizes out from the liquid ‘molasses’ when seeded with crystalline sugar.
Raw sugar is refined by washing away the contaminated outer coating of the crystals. The remaining sugar is then dissolved to make a 70% sucrose syrup. Impurities filtered out and further rounds of concentration and crystallization result in white refined sugar. Sugar crystals are again separated from the molasses in a centrifuge. Additional sugar is recovered as brown sugar. When no more sugar can be economically recovered, the final molasses still contains 20–30% sucrose, as well as 15–25% glucose and fructose. Granulated sugar is made by drying the sugar in a hot rotary dryer after which it is conditioned by blowing cool air through for several days.
Where is sugarcane grown?
Around 20 million ha of sugarcane are grown around the world (Fig 1). As a tropical crop, most is grown in Latin America, India and the Far East. Many countries in Africa individually grow small areas. Brazil, India, China, Thailand and Pakistan all grow more than one million ha. The area in Brazil has increased by 40% over the past decade.
Areas in India, Pakistan and the US have been fairly stable, but Cuba’s sugarcane area has decreased dramatically in recent years and in 2007 was down 66% on that in 1997.
The demise of the sugarcane industry in Cuba followed the collapse of the USSR and the guaranteed market it provided. Cane sugar is a major export for many Caribbean islands, but it is expected to collapse with the removal of the current system of preferred suppliers in the EU.
Over the past ten years, world production of sugarcane has increased by 25% to over 1.5 billion tonnes. This can be attributed to a 13% increase in harvested area and a 9% improvement in yield. Amongst leading countries, production of sugarcane has been increasing most in Brazil, China and Columbia. Some harvest data are shown in Table 1.
Table 1. Sugarcane production in leading countries (by area harvested) in 2008 (FAO forecasts).
|Country Area Harvested
| Average Yield
How is sugarcane grown?
Sugarcane is propagated from cuttings or ‘setts’ up to 1m long, planted in furrows. Shoots grow from buds on these stem sections. In Brazil, five or six harvests may be taken before replanting. ‘Plant cane’ is the new crop harvested about one year after planting (harvest is at the beginning of the rainy season – September to November) or more commonly 18 months after planting (harvesting in the dry period – July, August). After cutting, a ‘ratoon’ crop is grown from new shoots growing from the stumps of harvested plants. Ratoon crops are harvested at yearly intervals mainly in dry seasons. Careful application of nitrogen fertilizer is critical to high sugar yields. Too much encourages leaf growth rather than storing sugar. Ripening occurs naturally in cooler dry periods. Otherwise, it is hastened by withholding nitrogen and irrigation, and applying a chemical ripener such as trinexapac, sulfometuron or glyphosate.
Half of all sugarcane is harvested by hand. Before cutting, cane fields may be set on fire to burn away the leaves, which have sharp edges, to drive out snakes, and prevent weed seeds being returned to the soil. Cane stalks and roots are left unharmed. Cane burning is controversial because of adverse effects on soil and wildlife, as well as the danger of fires getting out of control, and is banned in some countries.
Harvesters which strip leaves and deposit them over the field provide an alternative to burning. This mulch cover reduces the impact of rain and helps prevent soil erosion. Sugarcane is often grown on sloping ground or on fragile soils. Tropical rainstorms cause a lot of soil erosion. Loss of topsoil reduces fertility and productivity, makes operations difficult where gullies have opened, and the eroded soil blocks water courses. Associated run-off of pesticides and nutrients may also reduce biodiversityDescription The 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 Resources http://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. and cause eutrophication in lakes and rivers.
Reducing soil cultivations also helps to minimise erosion. When preparing the land for a new crop, instead of plowing fields, weeds or a legume cover cropDescription Cover crops are primarily planted not to be harvested for food but to reduce soil erosion, control weeds and improve soil quality. They are usually plowed or tilled under before the next food crop is planted, in which cases the "cover crop" is used as a soil amendment and is synonymous with "green manure crop." Authoritative On-line References and Resources http://attra.ncat.org/attra-pub/covercrop.html ATTRA is the US National Centre for Appropriate Technology's Sustainable Agriculture Information Centre. grown while the land was fallow can be controlled by a non-selective herbicide such as paraquat. Paraquat has the advantage over systemic herbicides like glyphosate in that it very quickly kills shoots, leaving roots intact to improve soil structure and provide an anchoring effect to resist erosion. Cane setts are then planted in single furrows or narrow strips of tilled soil.
Protecting sugarcane crops
Weeds and integrated weed management
Weeds reduce sugarcane yields by competing for light, water and nutrients, by harboring pests and diseases, interfere with milling, and limit the number of ratoon crops. Weeds control can be one of the most costly components of sugarcane production. Perennial grassesDescription The leaves are "narrow" as opposed to the "broad" leaves of broadleaved weeds. Also called 'monocots' having one seed leaf opposed to 'dicots' having two seed leaves. Authoritative On-line References and Resources The International Weed Science Society represents individual associations around the world. such as guineagrass (Panicum maximum), alexandergrass (Brachiaria planteginea), johnsongrass (Sorghum halepense) and bermudagrass (Cynodon dactylon) are widespread serious weeds.
Residual herbicides which act in the soil on germinating weed seeds are widely used in sugarcane. However, although these herbicides give long term weed control, they have to move in the soil to be effective and can leach. Many are not totally selective to sugarcane and can cause damage. Paraquat is immobile in soil so cannot move to roots to damage the crop.
In ratoon crops which are mechanically harvested, using green leaf trash as a mulch helps to control weeds. The mulch shades out weeds and reduces new flushes of emergence after harvest.
Paraquat has a vital role to play in integrated weed management. Although glyphosate gives good control of perennial weedsDescription 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., its intensive use can encourage aggressive broadleaved weedsDescription 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. (eg morningglories, Ipomoea spp.), and even weed resistance. Paraquat gives excellent control of a broad spectrum of annual weedsDefinition Weeds that complete their life cycle within one growing season, or year. From seed to flowering to seed before the year ends. Authoritative On-line References and Resources The International Weed Science Society represents individual associations around the world., so it can be alternated with glyphosate to provide effective and sustainable weed control, reducing the risk of resistance.
A further advantage of paraquat is that it is not systemic. Glyphosate moves from leaves throughout plants and can easily seriously damage sugarcane. Paraquat, however, can be used between the rows of cane and small amounts of spray landing on crop leaves are harmless.
Weevils, borers, aphids and wireworms are all insect pests of sugarcane. Stem borers are most destructive. They are moth larvae which burrow into stalks, weakening them and causing loss of sucrose. In the US, the sugarcane borer (Diatrea saccharalis) is now controlled by a parasitic wasp (Cotesia flavipes). A famous example of a failed attempt at biological control was the introduction of cane toads (Bufo marinus) into Queensland, Australia, in 1935 from Hawaii in an attempt to control the larvae of cane beetles (white grubs). However, cane toads are now a serious pest. Poisonous venom is squirted from glands on their heads. They prey on native fauna like honeybees and transmit diseases to native frogs and fish. Insects are not the only pests of sugarcane. Rats can be a problem, and in Hawaii feral pigs have to be controlled.
Red rot (Colletotrichum falcatum) is a fungal disease of planted setts at low temperatures. Pineapple disease (Thielaviopsis parodoxa) also attacks setts causing the middles to blacken and smell like over-ripe pineapples. Rust (Puccinia melanocephola) appears as yellow to brown elongated oval pustules on both leaf surfaces. Yield losses can be as high as 20% and breeding for resistance is an important aim. Smut (Ustilago scitaminea) causes black whip-like organs to emerge from the rolled leaf sheaths, especially in SE Asia and South Africa. Bacterial diseases include gumming disease, Xanthomonas vasculorum, in which yellow stripes appear at leaf tips and cut stems exude a yellow gum; and leaf scald, Xanthomonas albilineans, in which yellow stripes occur on leaf blades and plants tiller excessively. Mosaic is a viral disease transmitted by aphids which causes stunting.