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Tolerance of Roundup Ready corn to a tankmix of Roundup plus MCPA for the control of field horsetail

Principal Investigator

Peter Sikkema

Research Institution

University of Guelph

Project Start

March 2012

Project End

February 2015


  • Determine the tolerance of Roundup Ready corn to a tankmix of Roundup plus MCPA.
  • Determine the most efficacious herbicides for the control of field horsetail in corn.


  • The determination of the best stage to apply a tankmix of Roundup plus MCPA in Roundup Ready corn infested with field horsetail allows the producer to have good weed management with minimal crop injury.
  • The determination that Broadstrike RC + MCPA provided good control of field horsetail in corn will allow a producer to have greater weed control options when managing field horsetail in corn.

Scientific Summary

Disclaimer: The information presented here does not constitute a recommendation by the researcher or Grain Farmers of Ontario. Always read and follow the pesticide label before use. Always ensure that you have the most current label.

Field horsetail (Equisetum arvense L.) is a competitive weed that is found in various regions of Canada. Field horsetail was historically found in undisturbed areas such as meadows, river banks, fencerows and; however, in recent years has moved into fertile grain fields as it has adapted to current agronomic practices. Field horsetail can grow to a height of 80 cm but is normally around 30 to 40 cm tall. Significant yield losses have been reported in corn with heavy field horsetail stands that can reach densities of 400 shoots per meter. Field horsetail due to its extensive and deep rhizomes cannot be adequately controlled with annual tillage as these practices only cut off the top growth. For each individual grower that has field horsetail in one or more fields, its presence can result in dramatic yield and monetary losses if cost-effective control measures are not identified. Ultim (group 2; nicosulfuron/rimsulfuron), Broadstrike RC (group 2; flumetsulam) and MCPA amine are postemergence (POST) applied registered herbicides in field corn that may have potential to control field horsetail applied alone or in combination.

This study investigated increasing doses of MCPA post-emergence at the V2 (4-leaf) and V6 (8-leaf) stages of corn. MCPA amine is a desirable compliment to the current weed management programs in glyphosate-resistant maize. There is little information on the sensitivity of glyphosate-resistant maize to glyphosate plus MCPA amine applied POST at various doses and application timings under Ontario environmental conditions. Determining the appropriate MCPA amine dose and application timing will help maize growers avoid crop injury and associated yield loss and provide an additional option for control of troublesome, glyphosate tolerant weeds such as field horsetail. The results indicate that the tolerance of corn to MCPA is application timing dependent and that corn is far more sensitive to MCPA as application timing is delayed and as the rate of MCPA is increased. MCPA applied postemergence provided 66% control of field horsetail in corn, while Broadstrike applied post-emergence provided 50% control. The application of either of these herbicides alone did not provide acceptable control of field horsetail. In contrast, the tankmix of MCPA plus Broadstrike applied post-emergence provided 83% control of field horsetail in corn.