The agrestal field violet, a pervasive weed in Europe, has been identified in reduced-tillage cereal fields in Alberta. The efficacy of herbicides in direct-seeded spring wheat was assessed on natural field violet infestations in Alberta in 2002 and 2003. Only fluroxypyr 2,4-D, applied postemergence, provided control of field violet in 2002 when rainfall was limiting. Over both years, this herbicide combination reduced biomass by 59 to 69% and plant density by 83 to 91%, relative to nontreated plots. The herbicides metsulfuron, sulfosulfuron, and thifensulfuron tribenuron only suppressed weed growth under drought conditions in 2002 but controlled the weed in 2003 when rainfall was greater, reducing plant density by 82 to 92% and rendering remaining plants sterile. Suppression was also observed with MCPA mecoprop dicamba in 2002 and 2003 and with metribuzin only in 2003. Effective control of field violet was conferred by a pre–crop emergence application of glyphosate at 445 g ae/ha in 2003, the only year that this treatment was evaluated. Activity of herbicides on three- to four-leaf seedlings was also evaluated in a greenhouse dose– response assay. All herbicides had greater efficacy in the greenhouse, and those that provided control in situ reduced field violet dry weight by 85% at less than the recommended rate used in field experiments. Management of field violet is possible with herbicides registered for use on spring wheat in Alberta. However, the weed does not appear to cause significant crop production losses; hence, herbicide selection should be based on knowledge of all weed species present within the field.
Nomenclature: 2,4-D; dicamba; fluroxypyr; glyphosate; MCPA; mecoprop; metribuzin; metsulfuron; sulfosulfuron; thifensulfuron; tribenuron; field violet, Viola arvensis Murr. #3 VIOAR; hard red spring wheat, Triticum aestivum L. ‘AC Barrie’.
Additional index words: Bentazon, direct seeded, herbicide evaluation, linuron, metribuzin, weed control.
Abbreviations: ALS, acetolactate synthase (EC 220.127.116.11); ED50, effective herbicide dose necessary to cause a 50% reduction in weed dry weight; ED85, effective herbicide dose necessary to cause an 85% reduction in weed dry weight; POST, postemergence; PREPLANT, pre–crop emergence; RU, reproductive units; WAT, weeks after treatment.