(1) Correlations between weather and the emergence of cohorts and correlation between weather, disease and grazing and subsequent cohort survivorship were investigated for the introduced annual Bromus tectorum in three habitat types in eastern Washington, U.S.A., for three consecutive generations. (2) Emergence of twenty out of twenty-four cohorts among the three sites in late summer to early autumn closely followed showers; emergence in spring could be related less commonly with isolated showers. (3) Emergence in winter probably did not occur until soil surfaces were free of snow and air temperatures were at or above 0?C; spring emergence was less predictable but occurred even as available soil moisture progressively declined. (4) [...]
