Herbicides support city living

Herbicides such as paraquat are now more important than ever as people who were raised in the countryside now choose to live in towns and cities. In Europe and North America, urban populations have exceeded rural ones for decades. As a result, no longer able to rely on an abundant supply of labor, farmers have adopted new technologies and production has had to intensify to ensure that crops are adequately cared for in order to produce enough food. Now, in Asia, urban populations are about to overtake rural ones and in less than 20 years Africa will follow suit (Fig 1).1 A recent paper in the journal Pest Management Science has reviewed the increasingly important benefits herbicides bring as the whole farming industry strives to ensure food security for all.2 Herbicides for weed control have been one of the key features of more intensive food production. Weeds compete with crops for the resources essential for good yields: light, water and nutrients. They may also attract pests and diseases, make crops difficult to harvest and contaminate foodstuffs with their seeds. Without effective weed control crops cannot make best use of fertilizer, further limiting yield potential. In fact, it has been estimated that weeds still deprive the equivalent of one billion people of food.3 Figure 1. Growth of rural and urban populations in regions across the world (FAO data). a) Rural populationsb) Urban populations              

 

 

Manual weeding problems

To be effective, hand weeding must remove weeds before they can compete with the crop. In countries across Asia, surveys have shown that it is increasingly difficult to find enough labor at the right time and at affordable wages to ensure that this happens. Often it falls to women and children to do the back-breaking work. Time spent weeding means time lost to education. It has been calculated that to adequately weed India’s crop fields, it would require nine billion person-days of labor. However, while herbicide use has been relatively low in the country (eg it was estimated that in 2005 herbicides were used to control grass weeds

Description

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. 
or 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.
on about 10% and 25% of wheat fields, respectively), in recent times it has been found that 15-30% of all major crop fields are never weeded, and more than 40% of fields are weeded too late to avoid weed competition.
In Africa, recent estimates are that yield losses resulting from the inability of smallholder farmers to hand weed at the appropriate time range from 25% to total loss. Smallholder maize yields are often 1 – 2 t/ha compared to 8 t/ha in research trials in the same area. Maize needs to be kept weed-free for eight weeks after planting. Maize is generally the first crop planted, but the later planting of cash crops is often prioritised over weeding the maize. In some African countries such as Mali, herbicide use has at least doubled since 2005.

Herbicide solutions

Non-selective

Description

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.
herbicides, led by paraquat, have enabled no-till

Description

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 for crop production to be established. If weeds are removed by herbicides before planting then there is no need to plow to bury weeds.

Benefits of a no-till system

  • Less labor needed
  • Erosion control
  • Water conservation
  • Less fuel used
  • Reduced greenhouse gas emissions
  • More biodiversity

    Description

    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.
  • Higher yields
In South America, adoption of no-till has been particularly successful in Brazil, Paraguay and Argentina, amongst other countries. In the south of Brazil, yield increases of 17% from no-till fields have been recorded. On sloping fields in Argentina, no-till reduced 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.
losses by 90% from 10 tonnes/ha each year. As a fast-acting herbicide, paraquat has several important advantages. With no systemic or soil residual effects, soil is further protected from erosion because roots remain to provide stability and there are no carryover problems for following crops that may be susceptible to other herbicides.
In fact, paraquat can complement the use of the slow-acting systemic herbicide glyphosate. These two essential herbicides have different modes of action and can, therefore, be used together to fight weed resistance. Having been so widely used for so long, glyphosate resistant weeds have become a concern to many farmers. In Brazil, a popular technique is to follow-up a pre-planting burndown spray of glyphosate with paraquat just before sowing to ensure no weeds escape control. Paraquat has many benefits on the farm, for the environment and for rural communities increasingly put under pressure to produce more food while people are flocking to the world’s cities.

References

  1. United Nations Department of Economic and Social Affairs. World Urbanisation Prospects 2011 Revision.
  2. Gianessi, LP (2013). The increasing importance of herbicides in worldwide crop production. Pest Management Science, 69, 1099-1105
  3. Berca (2004) referenced in here

Notes

The brand name of the leading paraquat product is Gramoxone.