Interference among Bean (Phaseolus vulgaris), Barnyardgrass (Echinochloa crus-galli), and Black Nightshade (Solanum nigrum)

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Abstract
The interference between dry bean (Phaseolus vulgarisL. var. Red Kidney), black nightshade (Solanum nigrum♯3SOLNI), and barnyardgrass (Echinochloa crus-galli♯ ECHCR) was examined in replacement series experiments. A modified replacement series experiment also was performed to examine the effects of no interference, and intraspecific and interspecific interference on the height, leaf area, and dry weight of bean, black nightshade, and barnyardgrass. In both types of competition experiments, bean germinated earlier than either weed species and caused significant reductions in weed height, leaf area, and dry weight. The impact of bean upon itself was always greater than the effect of either weed species. In laboratory studies, barnyardgrass and black nightshade seeds were subjected to eight concentrations of trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine). Black nightshade was 100 times more tolerant to trifluralin than barnyardgrass. Field studies, conducted at several locations in the Central Valley of California in which trifluralin-treated plots were compared with nontreated plots, demonstrated that trifluralin favors trifluralin-tolerant weeds (black nightshade), but trifluralin-sensitive weeds (barnyardgrass) have not been eliminated despite 20 yr of trifluralin use.