GREEN FOXTAIL (SETARIA-VIRIDIS) AND PALE SMARTWEED (POLYGONUM-LAPATHIFOLIUM) INTERFERENCE IN-FIELD CROPS

Field experiments were conducted at Vegreville, Alberta in 1984, 1985, 1986, and 1988 to determine the effects of green foxtail and pale sma rtweed on yield of wheat, barley, and canola. There was considerable v ariation among years in the response of crop yield to both weeds and i n the relationship between weed dry weight and weed density. Mostly re lationships between crop yield and either weed density or dry weight w ere poor, suggesting that the weeds competed weakly with the crops. Th us density or dry weight may be poor predictors of crop yield losses d ue to green foxtail or pale smartweed. Where the crops emerged ahead o f these weeds, and where soil moisture was not a limiting factor, crop yield losses were minimal and control with herbicides probably unecon omical. In some instances, growth and development of the weeds was sup pressed by the crops to the extent that little or no weed dry matter w as present at crop maturity. This was most evident with barley, and wh ere the crops emerged ahead of the weeds.