Crop desiccation

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Desiccated potato plants prior to harvest

Pre-harvest crop desiccation (also siccation[1]) refers to the application of a herbicide to a crop shortly before harvest.[2] Herbicides used include glyphosate, diquat and glufosinate.[2] For potatoes, carfentrazone-ethyl is used.[3] Other desiccants are cyanamide, cinidon-ethyl, and pyraflufen-ethyl.[4][5][unreliable source?]

Desiccation corrects for uneven crop growth which is a problem in northern climates during wet summers or when weed control is poor. Several additional advantages of desiccation have been cited: more even ripening is achieved and harvest can be conducted earlier; weed control is initiated for a future crop; earlier ripening allows for earlier replanting; desiccation reduces green material in the harvest putting less strain on harvesting machinery.[2] Some crop may be mechanically destroyed when crop desiccation machinery moves through the field.

The application of glyphosate differs between countries significantly. It is commonly used in the UK where summers are wet and crops may ripen unevenly. Thus in the UK 78% of oilseed rape is desiccated before harvest, but only 4% in Germany.[6]


Residue quantities are regulated by Codex Alimentarius of the Food and Agriculture Organization of the United Nations.[7] Several technical recommendations by governmental agricultural services suggest guidelines regarding sprays.[8] Pre-harvest desiccation is used in agriculture in crops including:


Glyphosate is used as a pre-harvest herbicide and harvest aid on cereal crops including wheat and oats and on oil seed rape.[14] As a systemic herbicide it is not a true desiccant as it can take weeks rather than days for the crop to die back after application.[15]

In the UK, it began to be applied to wheat crops in the 1980s to control perennial weeds such as common couch which was very effective and meant that sowing of the next crop could occur sooner. Use as a harvest aid in the UK increased after the introduction of strobilurin fungicides which prolong the longevity of the leaves,[16] and in 2002, 12% of UK wheat crops were treated.[17]

The timing of application is crucial as the moisture content of the grain must be below 30% for the yield of the crop to be unaffected and to minimise uptake of glyphosate by the grain.[18] Yield may be affected and residues increased if applications are made to uneven fields in which some areas have a moisture content over 30%. Although used in weed-free and evenly maturing crops with the aim of reducing the grain moisture content more rapidly to hasten the harvest, there is little or no advantage in doing so.[16]

Glyphosate was found in 5–15% of cereal crop samples tested in the UK between 2000 and 2004, although never exceeding the Maximum Residue Level of 20 mg/kg.[17] A survey of British wheat in 2006–8 found average levels of 0.05–0.22 mg/kg with maximum levels of 1.2 mg/kg.[19]

In July 2013 Austria banned the use of pre-harvest glyphosate citing the precautionary principle.[20] In April 2015 an oat buyer in Western Canada announced that it was refusing oats in which pre-harvest glyphosate had been used.[21][22]


  1. ^ "Assessment of large-scale test – Pre-harvest siccation in rape". Feiffer-consult. Retrieved 2 June 2013.
  2. ^ a b c d e "The agronomic benefits of glyphosate in Europe" (PDF). Monsanto Europe SA. February 2010. Retrieved 2 June 2013.
  3. ^ a b "Desiccation programmes". Potato Council. 2 August 2011. Retrieved 2 June 2013.
  4. ^
  5. ^ a b Brändli D, Reinacher S (January 2012). "Herbicides found in human urine". Ithaka Journal. Retrieved 3 June 2013.
  6. ^ Industry Task Force on Glyphosate (21 November 2013). "Preharvest weed control and desiccation". Retrieved 15 January 2014.
  7. ^
  8. ^$department/deptdocs.nsf/all/faq7206?opendocument
  9. ^ a b Province of Saskatchewan Dept of Agriculture. October 2010 Herbicide Options to Enhance Harvesting FAQ Archived 2015-06-01 at the Wayback Machine
  10. ^ Arnason, Robert (28 May 2015). "Richardson Milling says glyphosate dessication [sic] acceptable for its oats". The Western Producer. Retrieved 8 June 2015.
  11. ^ Robert Harris for Farmers Weekly. June 29, 2012 Challenging season for desiccating oilseed rape
  12. ^ Lulai EC. Skin-set, Wound Healing, and Related Defects. Ch 22 in Potato Biology and Biotechnology: Advances and Perspectives: Advances and Perspectives Eds. Vreugdenhil D et al, Elsevier, 2011 ISBN 9780080525051
  13. ^ Kozlowski TT. Extend and Significance of Shedding Plant Parts. Chapter 1 in Physiological ecology Shedding of Plants Parts, Ed. T.T. Kozlowski. Elsevier, 2012 ISBN 9780323145602
  14. ^ "Harvesting, Grain Drying and Storage - University of Saskatchewan". Retrieved 2017-05-03.
  15. ^ Brian Hall (12 August 2014). "Direct Harvest: Do you need a desiccant or a pre-harvest glyphosate?". Field Crop News.
  16. ^ a b J. H. Orson and D. H. K. Davies (June 2007). "Pre-harvest glyphosate for weed control and as a harvest aid in cereals" (PDF). Home-Grown Cereals Authority. Archived from the original (PDF) on 2015-06-15.
  17. ^ a b Pete Berry (November 2006). "FSA Pesticide Residue Minimisation Crop Action Plan - Cereals" (PDF). Food Standards Agency.
  18. ^ "RoundUp preharvest staging guide" (PDF). Monsanto - Roundup Product Page. Retrieved 3 May 2017.
  19. ^ E. D. Baxter, N. Byrd and I. R. Slaiding (November 2009). "Food safety review of UK cereal grain for use in malting, milling and animal feed" (PDF). Home-Grown Cereals Authority. p. 52.
  20. ^ Industry Task Force on Glyphosate (8 January 2014). "Preharvest use of glyphosate:Recent Austrian decision". Retrieved 5 January 2014.
  21. ^ Arnason, Robert (22 April 2015). "Oat buyer says no glyphosate pre-harvest". The Western Producer. Retrieved 8 June 2015.
  22. ^ Daniels, Calvin (30 April 2015). "Oats on forefront in industry news". Carlyle Observer. Retrieved 10 June 2015.

External links[edit]

Media related to Crop desiccation at Wikimedia Commons