Ripgut brome is a difficult weed to manage in cereal crops of southern Australia because only a few herbicides can provide effective control in cereals. Knowledge of seed-dormancy mechanisms, germination ecology, and emergence behavior in the field could facilitate development of effective weed control programs for this weed species. Ripgut brome populations from cropping fields were found to possess much longer seed dormancy than that reported previously in the literature. Furthermore, some ripgut brome populations from cropping fields showed longer seed dormancy than those collected from adjacent noncropped fence lines. For example, all seeds of one of the populations from the fence line (SA-1F) germinated at 3 mo after maturity, whereas seeds from the cropping field at the same site (SA-1C) showed little germination (< 3%) even at 8 mo after maturity. These highly dormant ripgut brome populations from cropping fields were responsive to cold stratification, with germination increasing significantly after 2 to 14 d of exposure. Germination of dormant ripgut brome populations increased with addition of gibberellic acid (0.001 M GA3), particularly when lemma and palea had been removed. Ripgut brome populations from cropping fields (VIC-2C and SA-1C) showed strong inhibition of seed germination when exposed to light. These differences in seed dormancy among ripgut brome populations were also expressed in seedling emergence pattern in the field. The nondormant populations collected from fence lines showed high seedling establishment (> 80%) during autumn, which coincided with the planting time of winter crops in southern Australia. In contrast, five populations from cropping fields showed much lower seedling establishment (3 to 17%) before the time of crop planting. Delayed seedling establishment in populations from cropping fields could lead to less effective preseeding weed control and higher weed infestations in field crops. Results of this study also showed that the seedbank of these highly dormant ripgut brome populations can readily persist from one year to the next. Effective management of ripgut brome populations with long seed dormancy and increased seedbank persistence would require a major change in cropping systems used by the growers in southern Australia.

A model that describes the emergence of ripgut brome was developed using a two-season data set from a no-tilled field in northeastern Spain. The relationship between cumulative emergence and hydrothermal time (HTT) was described by a sigmoid growth function (Chapman). HTT was calculated with a set of water potentials and temperatures, iteratively used, to determine the base water potential and base temperature. Emergence of ripgut brome was well described with a Chapman function. The newly-developed function was validated with four sets of data, two of them belonging to a third season in the same field and the other two coming from independent data from Southern Spain. The model also successfully described the emergence in different field management and tillage systems. This model may be useful for predicting ripgut brome emergence in winter cereal fields of semiarid Mediterranean regions.