Bearded sprangletop is a problematic weed in California rice production. The objective of this research was to determine the response of two bearded sprangletop biotypes (clomazone-susceptible [S] and -resistant [R]) to flooding depth. A study was conducted in 2017 and 2018 at the California Rice Experiment Station in Biggs, CA, to evaluate the flooding tolerance of the two biotypes against 5-, 10-, and 20-cm continuous flooding depths. Plant emergence, plant height, panicles per plant, seed per panicle, 100-seed weight, and seed per plant data were collected. At the 5-cm flood depth, neither biotype was controlled, and the R biotype had 260% more emergence, produced 475% more panicles per plant, and 455% more seed per plant than the S biotype. With a 10-cm flood, only the R biotype survived flooding and produced more panicles per plant and seed per plant than any other flood depth-biotype combination evaluated. There was no emergence of either bearded sprangletop biotype at the 20-cm flood depth. Continuous flooding can still be used as a management tool to control bearded sprangletop; however, the depth of flooding appears to limit emergence of S biotypes at 5 cm and R biotypes at 10 cm, and completely inhibits growth of both biotypes at 20 cm. The results of this study indicate that clomazone-resistant bearded sprangletop is more likely to spread throughout the Sacramento Valley because this biotype can survive clomazone applications and can tolerate a standard 10-cm flood.
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