Paraquat for citrus

Citrus fruit make-up a vast family including not only oranges, lemons, limes and grapefruit, but also calamondins, citrons, pomelos and ugli fruit.

Integrated pest management (IPMDescription 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 have been introduced to minimize the impact of citrus growing on soil, water, air and 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 has a key role in sustainable citrus production by controlling weeds that would otherwise seriously reduce productivity.  It can be used in conjunction with other techniques to manage 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., particularly the use of strips of grass or legume 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. between trees.

Paraquat can be safely sprayed to manage the weed flora along the crop rows between the grass or legume strips without fear of damaging the citrus trees.  Paraquat is immobile in soil and cannot move to the roots and up into the shoots.  Tree bark cannot be penetrated by paraquat meaning that it can be sprayed right up to the base of the trees.  Even if paraquat drifts onto citrus leaves there is little or no damage because paraquat does not move through plants like glyphosate does.

Citrus fact file

  • 1:  Brazil is the leading citrus growing country
  • 8.7 million ha of citrus are grown worldwide
  • 48% are oranges, 25% mandarin types, 12% lemons and limes, 3% grapefruit
  • 33% of crops are grown for juice
  • 10 years for a tree to bear a full harvest

Traditionally, and in poorer farming communities, citrus groves are hoed by hand to remove weeds.  This is labor-intensive and time-consuming, and, therefore, can limit opportunities for other activities, including education.  Effective use of herbicides can very significantly reduce the resources needed to control weeds.  The most commonly used herbicides include paraquat and glyphosate which have no activity in the soil, and the class of herbicides known as ‘residuals’ which remain active in the soil and prevent the germination of weed seeds.

Intensive use of glyphosate and residuals has led to changes in weed flora (‘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.’) as species more tolerant to their particular modes of action become more dominant.  ‘Soft’ weeds, typically prostrate annual 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.  which are easily controlled, are replaced by re-invasion of cleared land by more aggressive, pernicious weeds, which reduce crop yields.  These compete with citrus trees to reduce yield and quality and may make harvesting difficult.

Grass or cover crop strips between tree lines reduce soil erosionUsing paraquat, however, to manage the weed flora rather than eliminate it, can help to maintain a balanced flora, which precludes the dominance of aggressive species.  Paraquat only removes the top growth of well-established weeds, and does not affect the germination of new seedlings allowing vegetation to re-establish after 1-2 months.  A controlled presence of soft weeds maintains the balance of the weed flora and prevents weed shifts to more competitive species simply because bare ground for them to colonize is less available.  The presence of non-competitive vegetative cover also provides habitats to encourage biodiversity.  The wildlife encouraged will include predators of insect pests, which would otherwise have to be controlled chemically.