A study was conducted to quantify the magnitude and sources of variation in common waterhemp temporal patterns of emergence over 1 yr. In 2008 and 2010, emergence patterns in the absence of soil disturbance were determined for replicated samples of maternal families (progeny from one individual) separately harvested during the previous year from four plants within each of four agricultural fields (16 maternal families yr−1) at a university research farm near Urbana, IL. Combining data across years, variance partitioning indicated that seed sample within maternal family explained 48% of total variation in the percentage of viable, buried seeds that produced seedlings. Differences within, rather than among, maternal families also accounted for large fractions (60 to 99%) of total variation in cumulative percentage emergence at specific points during the growing season. Within years, seed samples characterized by delayed or accelerated emergence patterns did not originate from specific maternal plants. These results indicate that common waterhemp seed populations are without strong maternal plant effects that limit emergence to narrow intervals within the overall emergence period. Thus, results of this study support the use of contemporary approaches for modeling herbicide resistance evolution in common waterhemp, which assume seedling cohorts contain offspring from all individuals occurring within the maternal population.

Annual bluegrass is a cosmopolitan, cool-season grass that adapts to different environmental conditions. It is one of the main weeds of turfgrass, and its control is mainly achieved through chemical and cultural practices, although little importance is given to the competitive ability of turfgrass species or cultivars. A field study was performed in northeastern Italy from October 2012 to June 2014 to evaluate the competitive ability of selected perennial ryegrass cultivars to suppress emergence and establishment of annual bluegrass seedlings. Two creeping perennial ryegrasses (‘CSI' and ‘PPG-PR171’) and two traditional cultivars (‘Azimuth' and ‘Presidio') were compared. In late autumn in both years, annual bluegrass was sown in a marked area (30 cm by 30 cm) in the turfgrass. Emerged seedlings were counted weekly, and emergence dynamics were modeled. In the second year, final density of annual bluegrass allowed to grow in turfgrass was also evaluated in summer. Results showed that both seedling emergence and density of annual bluegrass were significantly reduced by creeping perennial cultivars, supporting the hypothesis that these cultivars may reduce annual bluegrass establishment in turfgrass. Seedling emergence pattern of annual bluegrass did not differ in creeping and traditional cultivars of perennial ryegrass, suggesting the possibility of creating a general emergence model suitable in any turfgrass to help turfgrass managers in the control of this weed species.