Effect of Rice Winter Cultural Management Practices on the Size of the Hatching Population of Triops longicaudatus (Notostraca: Triopsidae) in California Rice Fields

The tadpole shrimp [Triops longicaudatus (Leconte)] has emerged as a significant pest of rice grown in California in recent decades. The change in T. longicaudatus' pest status has coincided with changes in cultural management of residual rice straw postharvest. Policy changes have reduced the postharvest burning of fields from nearly 95% to less than 10%, promoting increased use of winter flooding as a means of accelerating straw decomposition. Field and laboratory trials were conducted from 2015 to 2017 at the Rice Experiment Station in Biggs, CA and in greenhouses at the University of California (UC) Davis to evaluate the effects of burning, flooding, and a fallow control on T. longicaudatus population dynamics. Experiments demonstrated that burning of rice straw failed to suppress densities of hatching T. longicaudatus and actually had the reverse effect, causing a 51% increase in numbers hatching, perhaps as a result of burning triggering termination of multiyear T. longicaudatus egg dormancy. Winter flooding had no measurable effect on T. longicaudatus hatch. Thus, these changes in winter cultural practices do not appear to be responsible for the emergence of T. longicaudatus as a major rice pest.