Influence of variable rates of imazamethabenz and difenzoquat on wild oat (Avena fatua) seed production, and wheat (Triticum aestivum) yield and profitability

Abstract

Field experiments to investigate the effects of variable imazamethabenz rates on wild oat seed production and wheat yield and profitability were conducted at Lacombe, Lethbridge and Vegreville, Alberta, and Kalispell, Montana, over several years. Similar studies with difenzoquat were conducted at Lacombe and Lethbridge. In most cases, reducing the herbicide rates below those recommended resulted in increases in wild oat seed production, but the potential for returning relatively large amounts of wild oat seed to the soil seedbank depended on the extent of the rate reduction. For example, averaged over locations and years, reducing the rate of imazamethabenz to 75% of the recommended rate resulted in wild oat seed production increasing by 25% compared with an increase of over 100% when the rate was reduced to 50%. Wheat yields and economic returns as functions of rate also varied for both herbicides. It was more economical, in most cases, to apply imazamethabenz at 50 or 75% of the recommended rate compared with the full rate. However, an economic loss occurred in four and three of the 11 location-years when the imazamethabenz rate was reduced to 50 and 75%, respectively, and losses were more severe at the 50% rate. Compared with imazamethabenz, reducing the rate of difenzoquat tended to be more risky in terms of increased wild oat seed production and reduced net economic return. Key words: Reduced herbicide rates