COMPETITION OF SAPONARIA VACCARIA AND SINAPIS ARVENSIS IN WHEAT

Abstract

Sinapis arvensis L. (wild mustard) competed strongly with Saponaria vaccaria L. (cow cockle) in wheat on heavy clay soil. Seed and dry weight production by S. vaccaria were reduced about half by 190 S. arvensis plants/m2. S. vaccaria at 314 plants/m2 had little effect on S. arvensis. Support was obtained for the hypothesis that populations of S. vaccaria increased after 2,4-D came into general use and this species was no longer suppressed by S. arvensis. S. arvensis at 190 plants/m2 reduced grain yield 38% and 314 S. vaccaria/m2 reduced it 36%. Competitive effects of both species together were not fully additive because the effects of one species tended to obscure the effects of the other. Intraspecies competition was demonstrated in each weed species by its decrease in productivity per plant as its density increased.