Seed deterioration, and therefore seed germination potential, are highly influenced by relative humidity and temperature. However, limited species-specific information is available about the effect of long-term soaking in water on seed germination potential. Knowing the potential fate of a creeping bentgrass seed that falls in an irrigation canal is important for the study of transgene flow in this species at the landscape level. The objectives of this study were to evaluate the effect of soaking time and water temperature on germination of creeping bentgrass seed and to assess how fast a panicle could be moved in an irrigation canal. Germination was determined for seeds from panicles of three cultivars of creeping bentgrass that were soaked in water for up to 17 wk at two water temperatures, 4 and 20 C. Creeping bentgrass seeds did not lose their ability to germinate after 17 wk in water at 20 C and, although reduced, germination was still 46% after 17 wk in water at 4 C. The reduction in germination in seeds from panicles kept in water at 4 C was due to the induction of secondary dormancy, which was overcome by dry seed storage at room temperature. We quantified that a panicle that falls in an irrigation canal has the potential to travel downstream at an average rate of 19 m min−1 and move seeds that could potentially establish seedlings elsewhere. Therefore, movement of creeping bentgrass seed by water has to be considered as a means of gene flow.

Controlled-environment experiments were conducted to predict the dispersal distance of horseweed seed. Seed were released from a fixed height and collected at three distances from the introduction point along a 6-m wind tunnel. Dispersal potential was assessed at wind speeds of 8 and 16 km hr−1 and release heights of 50.8 and 76.2 cm. In separate experiments, settlement velocity was determined to be 0.323 m sec−1 (SD = 0.0687). These data were used to parameterize a mechanistic model and compared to a quantile extrapolation (QE) of wind-tunnel results. The QE method predicted a greater mean dispersal distance than the mechanistic model, with large disparities between maximum dispersal distances. Quantile extrapolation predicted dispersal distances over 100 m, whereas the mechanistic model predicted a maximum distance of approximately 30 m. Air turbulence within the wind tunnel and complex dynamics of seed flight may have contributed to the discrepancy between models. Predicting the mean and numerical distribution of seed dispersal distance is crucial when estimating the spread of wind-dispersed seed and for the design of a field-sampling protocol. Although controlled-environment experiments lack the wind variability present in natural systems, predictions from wind-tunnel studies provide a better first approximation of dispersal distance than the mechanistic model. Field experiments designed on the basis of these outcomes are more likely to capture the true dispersal distribution. This should provide more accurate data to inform management decisions for wind-dispersed species.

Information linking seed movement, along with changes in seed viability, is critical for understanding weed seed dynamics. Studies were conducted to examine the use of passive integrated transponder (PIT) tags placed in nylon mesh packets in combination with GPS (Global Positioning System) technology to track weed seed movement after tillage. Cylindrical PIT tags 11.5, 12, 20, and 23 mm long by 2 mm wide were evaluated in water and soil. Detection improved as tag size increased because of greater signal strength. Tags with the main axis oriented vertically were recovered at greater depths than when placed horizontally. Average detection depths for 12-mm PIT tags were 29.5 cm in water, 18.2 cm in sand, 24 cm in artificial soil, and 21.2 cm in sandy loam soil. Tests also showed that PIT tags and nylon mesh packets were resilient to intense tillage with a rototiller. No significant differences in displacement because of tillage were observed between free PIT tags and PIT-tagged packets. PIT tag performance was further tested in a 2-yr field experiment conducted between September 2003 and October 2005 at six sites in Nebraska and Wyoming. Tilled and no-till blocks were established at each site. PIT-tagged packets in the tilled block and untagged packets in the no-till block were used. Sample burial depths were 0, 2.5, 7.5, and 15 cm. Sample recovery rate did not differ between tilled and no-till blocks. Time of recovery was the main factor affecting recovery of packets buried at 0 and 2.5 cm in both blocks. Seed predation by small rodents and movement of samples beyond the area of study by tillage implements were the main sources of packet loss. Nevertheless, 2 yr after initiation of the study, more than 85% of the samples were recovered. Future development of PIT tag technology will lead to an enhanced ability to monitor seed movement.