Paraquat gives flexible weed control in potatoes

Potatoes saved from weeds by paraquatControlling weeds in potatoes is a problem for many farmers. Paraquat is a very useful herbicide for potatoes because it can be used to burndown weeds from before planting right up to the point at which the potato sprouts start to emerge from the soil1. This allows for weed control measures to be tailored to the weeds present. As potatoes may take up to four weeks to emerge, significant weed growth may have occurred after planting. Weeds can quickly overrun potato crops if they are allowed to grow unchecked before the crop leaf canopy closes. They compete with potato plants for light, water and nutrients, so if they are not controlled weeds reduce yield and quality. In addition, large weeds entangle the crop and interfere with harvesting. Weeds may also encourage pests and diseases. Filling the crop canopy, they restrict air flow, increasing humidity under which fungal diseases, especially potato blight (Phytophthora infestans) thrive. Blight can devastate potato crops so intensive use of fungicides is needed to achieve control. Paraquat is inactivated and immobilised immediately on contact with the soil, so cannot affect the seed potatoes, or later, the developing crop of tubers.

Potato Facts2,3

  • Over the past 20 years potato production has doubled in developing countries.
  • More potatoes are grown in China than in any other country – 4.6 million ha were harvested in 2008.
  • Other leading potato growing countries are Russia (2.1 m ha), India (1.8 m ha), Ukraine (1.4 m ha) and Poland (0.5 m ha).
  • The country growing the highest yields of potatoes is Belgium – 46 t/ha. High yields are also grown in the US, New Zealand and other countries in NW Europe.
  • 5,600 kcal of energy fixed per 1000 litres of water used (45% more than maize, 140% more than wheat, 180% more than rice)
  • Twice as much protein produced per unit of water transpired as wheat
  • 181 kg eaten by the average person each year in Belarus

Sustainable potato production

2008 was the United Nations’ International Year of the Potato3. A book of guidelines for sustainable production was written to build on the experiences shared during 20084. Principles of Good Agricultural Practice


Refers to the package of recommendations and available knowledge to address environmental, economic, and social sustainability for on-farm production and post-production processes resulting in safe and healthy food and non-food agricultural products. GAP may consist of guidelines addressing issues of site selection, adjacent land use, fertilizer use, water sourcing and use, pest control and pesticide monitoring, harvesting practices (including worker hygiene, packaging, storage, field sanitation, and product transportation), and cooler operations.

Authoritative On-line References and Resources The UN FAO provides independent information on GAP programmes, practices and standards.
recommended include:
  • Managing the soil in potato fields to reduce erosion
  • Maintaining or restoring soil organic matter levels
  • Maintaining soil structure
  • Reduce water loss and improve infiltration
All these aims can be met by reducing unnecessary soil tillage. Excessive tillage degrades soil and results in erosion on sloping terrain, eg in the foothills of the Andes in South America, the region where potatoes originated. There, the traditional way to prepare fields for planting potatoes is by ploughing and cultivating two or three times. Authorities in Colombia estimate that an average of 20 tonnes of soil are lost every year from each hectare of cultivated land across the country. In extreme cases erosion losses may reach 100 tonnes of soil per hectare. Eroded soil is eventually deposited in ditches, rivers and lakes, blocking water flow. Mineral nutrients in sediment and rainfall run-off


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
cause algal blooms which exhaust dissolved oxygen and reduce biodiversity


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 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.
in affected water.
Recently, in a program focused on the safe and effective use of paraquat, 4,000 famers in the Cundinamarca region of Columbia were trained in conservation agriculture techniques5. A number of demonstration plots were established to show farmers how to adopt conservation agriculture approaches with their potato crops. They were shown how soil degradation could be avoided by adopting the three pillars of conservation agriculture:
  1. Minimal soil tillage
  2. Use of cover crops


    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 ATTRA is the US National Centre for Appropriate Technology's Sustainable Agriculture Information Centre.
    or keeping stubbles between crops
  3. Use of appropriate crop rotations
After being trained, farmers appreciated the benefits of reduced costs and conservation of soil moisture by using minimal tillage, as well as much less soil erosion


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 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.
. With no plowing to bury them, weed control has to be accomplished by herbicides. Paraquat’s fast action, broad-spectrum and inactivation on soil contact make it an ideal choice. The adoption of conservation tillage


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.
by farmers attending demonstration days was 37% compared to only 7% in communities outside the project zone.


  1. Murphy, H J et al (1970). Pre and early post-emergence weed control with paraquat in potatoes. American Journal of Potato Research, 47, (7), 252-255
  2. FAO crop statistics
  3. UN Year of the Potato
  4. FAO (2008). Sustainable potato production: guidelines for developing countries