M.Sc. Defence: Tessa de Boer


Interested Members of the University Community are invited to attend the Final Oral Examination for the Degree of Master of Science of Tessa de Boer of the Department of Plant Agriculture

Date & Time: Wednesday May 16 at 1:00 PM
Location: Room 121 B, Crop Science Building

Thesis Title: A Linuron-Free Weed Management Strategy for Carrots

Advisory Committee
Clarence Swanton, Advisor
Rob Nurse
Darren Robinson
François Tardif 

Examination Committee
Eric Lyons, Chair
Clarence Swanton
François Tardif 
Mary Ruth McDonald                                                                                                                                                          


The development of a linuron-free weed management strategy for carrot production is essential as a result of the herbicide re-evaluation programs launched by the Pest Management Regulatory Agency in Canada for herbicides registered prior to 1995 and the recent discovery of linuron resistant pigweed species in Ontario. In 2016 and 2017 field trials were conducted in one of Ontario’s main carrot growing regions on high organic soils. Pigweed species seedlings were effectively controlled with pre-emergent treatments of prometryn, pendimethalin, s-metolachlor, or glufosinate. Post-emergent treatments of pyroxasulfone and metribuzin followed by the predetermined biologically effective dose (≥90% control of pigweed seedling) of acifluorfen, oxyfluorfen, fluthiacet-methyl, and fomesafen achieved excellent crop selectivity and commercially acceptable pigweed seedling control under field conditions. Carfentrazone-ethyl or fomesafen applied pre-emergent severely reduced emergence and in turn, yield in the wet growing season of 2017. This study demonstrated clearly that an alternative linuron-free strategy can be developed for carrots. The novel strategy of exploring the potential to utilize the biologically effective dose of selected herbicides to achieve crop selectivity and control of pigweed seedlings was verified.