HOUSTON, Texas (AP) — Texas health officials say that because of the rains brought by Hurricane Harvey, aerial spraying targeting mosquitoes is set to start this week in two Southeast Texas counties.

The Texas Department of State Health Services said Wednesday that aerial spraying is set to start around dusk Thursday over Refugio and Bee counties. The health department said it had activated its contract for aerial mosquito control and requested additional mosquito control assistance from the Federal Emergency Management Agency.

Health officials say that while most mosquitoes that appear after floods are nuisance mosquitoes that don’t spread disease, they can impact recovery operations by preventing responders and those affected by a disaster from being outside. Also, standing water can increase the number of mosquitoes capable of spreading diseases like West Nile virus and Zika.

Health officials say a small amount of insecticide — one to two tablespoons per acre — will be dispersed by airplanes equipped with nozzles that create ultra-low volume droplets that kill mosquitoes.

To treat the upper Texas coast, the state is calling in help from the U.S. Air Force Reserve’s 910th Airlift Wing, which will be using their C-130H cargo planes.