Paraquat for sugarcane

Sugarcane is a tall grass with a thick fibrous stem which stores sucrose. As a tropical crop, most is grown in Latin America, India and the Far East. About 70% of all sugar comes from sugarcane, the rest from sugar beet.

Controlling weeds with paraquat and using associated agronomic practices can help overcome several major environmental issues in sugarcane production including:

  • Soil erosion

    Description

    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-off

    Description

    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 leaching

    Description

    The natural process by which water soluble substances are carried downward through the soil into groundwater.

    of agrochemicals
  • 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 other herbicides such as glyphosate

Soil erosion

Paraquat has been essential to the development of cultivation systems like no-till which do not rely on plowing for weed control. The less the soil is disturbed, the more erosion is avoided. 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 biodiversity and cause eutrophication in lakes and rivers.

When preparing fields for a new crop, instead of plowing, weeds or a legume cover crop 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.

Agrochemical leaching

Paraquat is deactivated immediately on contact with the soil, so there are no run-off, leaching, persistence or root uptake problems to restrict its use. 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, so running the risk of leaching. 

Sugarcane fact file 

  • 26 million ha of sugarcane are grown around the world
  • 101 countries grow sugarcane
  • 1.8 billion tonnes were harvested in 2012
  • No. 1 country for sugarcane production is Brazil
  • 25% increase in area of sugarcane in Brazil since 2000

Weed resistance

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 which regrow from an original planting. Weed control can be one of the most costly components of sugarcane production.

Paraquat is not systemic like 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.

Although glyphosate gives good control of perennial weeds, its intensive use can encourage aggressive broadleaved weeds and even weed resistance. Paraquat gives excellent control of a broad spectrum of annual weeds, so it can be alternated with glyphosate to provide effective and sustainable weed control, reducing the risk of resistance.