Studies were conducted both in the field and laboratory to investigate tillage as a means of controlling the production of floodwater mosquitoes, primarily Aedes vexans, in grassy depressions and river floodplains. Tractor plowing followed by disking produced control of mosquitoes ranging from 73 to 100 percent. This method of tillage displaced mosquito ova from the top 12.0 mm of the soil substrate to depths of 126 mm or more thereby trapping larvae in the soil and preventing their further development and emergence as adults. Laboratory studies confirmed that this action produced the control effect since essentially all eggs in all tests hatched, yet larval emergence decreased as soil cover over the eggs increased.