Effects of ’volunteer’ Wheat and Barley on the Growth and Yield of Rapeseed

Field experiments were conducted in 1982 and 1983 to determine the effects of increasing densities (0–60 plants m −2 ) of ’volunteer’ wheat (Triticum aestivum L. ’Neepawa’) and barley (Hordeum vulgare L. ’Bonanza’) on the growth and seed yield of rapeseed (Brassica napus L. ’Regent’). The results were plotted using linear regression analysis and described by the equation[Formula: see text]where y = biomass or yield (g m −2 ); b 0 = intercept; b 1 = linear regression coefficient and x 1 = density of ’volunteer’ plants m −2 . From the results obtained in 1982 and 1983, ’volunteer’ wheat interference reduced rapeseed yields as described by the equations[Formula: see text]and[Formula: see text]respectively. Similarly, the reduction in rapeseed yield in the two years caused by ’volunteer’ barley was described by the equations[Formula: see text]and[Formula: see text]Thus, an intermediate density of 30 ’volunteer’ wheat plants reduced the yield of rapeseed by approximately 17% in both years; whereas, an equivalent density of ’volunteer’ barley plants reduced rapeseed yields by approximately 27% in 1982 and 35% in 1983.