Kochia (Kochia scoparia) and Wild Oat (Avena fatua) Intraspecific and Interspecific Interference

Kochia (Kochia scoparia) and wild oat (Avena fatua) are highly problematic western Canadian weeds. Wild oat is widely distributed and has been a long-standing agricultural pest across Manitoba, Saskatchewan, and Alberta. Kochia populations are patchy and occur more frequently within the southern regions of the Prairie provinces. Kochia is exhibiting an ever-evolving, aggressive, herbicide resistance survival strategy which may facilitate range expansion. The experimental objective was to study the interspecific and intraspecific interference between wild oat and kochia. The study was developed with the context of kochia tumbleweeds travelling and depositing seed within wild oat infestations. Greenhouse experiments were conducted in Saskatoon, SK. The experimental design was a two factor factorial arranged as a randomized complete block. The main factors were kochia and wild oat pot density at either 0, 1, or 2 plants per pot. Treatment combinations resulted in species ratios of 1:1, 2:1, 1:2, and 2:2, with single species controls. Kochia biomass was reduced by >70% after 3 months of competition with a single wild oat plant. Wild oat biomass was consistently impacted by intraspecific competition, demonstrating a 25 to 50% reduction at the trial end. Kochia interspecific interference with wild oat at a 2:1 ratio did reduce wild oat biomass by 50% but this trend was not consistent across experimental runs. Kochia dispersal through wild oat infestations should induce competitive stress when crop competition is considered. Three-species interference patterns to include western Canadian crops require additional study.