Paraquat for cotton
Cotton is a fibre which protects the seed of the cotton plant, much as the flesh of an apple protects the pips.
In 1997, GM cotton tolerant to the 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 glyphosate was introduced. Although herbicide tolerant cotton has many advantages, it has contributed to enormous increases in the use of glyphosate which is now posing problems by encouraging the development of resistant weeds which are no longer controlled by this herbicide.
No more than two applications of glyphosate should be applied to any one field over two seasons. Paraquat can provide the alternative means of effective and sustainable weed control.
Using paraquat in weed control programmes can also address a number of environmental issues concerned with cotton growing including 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. and degradation, 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, and loss of habitats and effects on 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..
Paraquat is deactivated on contact with the soil meaning that it can be sprayed to burndown weeds before planting a cotton crop without risking damage to that crop or indeed subsequent crops in the rotation. It does not pollute soil or surface waters because it is immobilised and deactivated immediately on contact with soil. So, there are no leaching, persistence or root uptake problems to restrict its use, unlike many other herbicides which have ‘residual’ properties. Paraquat works well even in cold and rainy weather, unlike most herbicides, making it suitable for early season burndown.
Cotton fact file
- 30 million ha of cotton are grown worldwide
- 85 countries grow cotton
- 44% is grown on the Indian sub-continent
- 75% of US cotton is GM glyphosate tolerant
- 25 tonnes/ha of soil are eroded each year from the cotton fields of Alabama, USA
Broad-spectrum herbicides, led by the introduction of paraquat in the 1960’s, have allowed the adoption and growth of soil cultivation systems which do not rely on controlling weeds by burial from plowing. Abandoning the mouldboard plow in reduced or 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. systems saves cash, time and fuel, improves soil structure, reduces erosion and provides havens for wildlife.
More recently, 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 have been developed as a wider approach to crop production than tillage alone. These include the use of cover cropsDescription 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. and mulches of residues of previous crops to ensure at least 30% of the soil surface is always covered to prevent soil erosion. Also, the managed, non-competitive vegetative cover provides habitats to encourage biodiversity.
In recent years, intensive use of glyphosate has caused new weed problems as species less well controlled have ‘shifted’ to become more dominant and 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 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, is helping 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.
Although paraquat is a non-selective, broad spectrum herbicide, if small amounts land on leaves there is little or no crop damage because paraquat does not move through plants systemically like glyphosate. So, paraquat can be used for inter-row weed control in cotton to remove weeds growing between the crop rows.