Cowlitz County district staff conducts surveillance and abatement activities through the active mosquito season, usually February 1st through August 31st, each year. The priority is to attack mosquitoes at their source, by treating mosquito larvae as they hatch. It is far more effective to reduce mosquito populations at their source, before they fly into neighborhoods, than to fog large, open areas to eliminate adult mosquitoes. It is very difficult to reduce mosquito populations once they have spread from the breeding source. Helicopter applications, for mosquito larval control, may take place during the months of April through September, depending on mosquito breeding habits and/or weather conditions.
Control measures used by staff comply with policies adopted by the Board of Trustees of the Mosquito Control District and with state and Environmental Protection Agency regulations. Biological control methods are used that have the least adverse effect on humans, pets, wildlife, and the environment.
Field technicians implement an Integrated Mosquito Management (IMM) program and uses a variety of products and equipment to control mosquitoes. Treatment methods in Cowlitz County include larvicide applied by helicopters, drone, broadcast from trucks, and on foot from backpack applicators. Larvicide briquettes are placed into storm drains and catch basins. Limited treatment is applied to adult mosquitoes due to the limited effectiveness of this method and the short duration of the materials.