A series of ground and aerial applications of Lagenidium giganteum, a facultative fungal parasite of mosquito larvae, was made in rice fields and associated habitats in the Sacramento Valley, CA. Initial trials using ground applications of the fungus in 400 m2 plots indicated that asexually competent mycelium from 30 liters of fermentation beer per hectare was sufficient to control Culex tarsalis in rice field habitats. Two multi-hectare applications using a Micronair Atomizer were made at rates of mycelium from either 20 or 30 liters of fermentation beer per hectare. The lower application rate resulted in 40% confirmed infection of Cx. tarsalis and Anopheles freeborni sentinel larvae, while the higher application rate resulted in greater than 90% initial mortality of sentinel Cx. tarsalis and An. freeborni and 65% Aedes melanimon sentinel mortality. This was accompanied by a 10-fold decrease in indigenous populations of the 2 former species.