White mustard (Brassica hirta Moench) and foxtail millet (Setaria italica (L.) Beauv.), thinned to uniform stands, varied in a three-year study in their effects on peas depending on weed population, duration of competition, relative time of pea and weed emergence, and year to year variations in seasonal rainfall. Full-season competition from 3 mustard plants per square foot reduced pea stands 0 to 25%, pea vine weight 39 to 71%, and yields of shelled peas 0 to 64%, during the three years. In one direct comparison, 27 foxtail plants per square foot caused reductions in peas comparable to those caused by 3 mustard plants. When mustard emerged 3 days before peas, fresh weight of pea vines was reduced 54 percent; but when mustard emerged 4 days after peas, only 17 percent.

The relative growth rates of peas, Brassica hirta, B. Kaber, Amaranthus retroflexus, Polygonum Persicaria, Setaria italica, S. viridis, S. glauca, and Echinochloa crusgalli grown without intra- and inter-species competition suggest that the Brassica species would be the more severe competitors with peas and that weed competition usually would be more severe in late-seeded peas.