Texas health officials say the Federal Emergency Management Agency will use military planes to spray chemicals near Houston to help control disease-carrying mosquitoes following Hurricane Harvey.

Texas Health and Human Services spokesman Chris Van Deusen says spraying began Saturday evening east of Houston, in Jefferson, Orange and Chambers counties.

Harvey’s rains flooded the region. Standing water is a breeding ground for mosquitoes, including those that carry the West Nile and Zika viruses.

Van Deusen says there haven’t been reports of the viruses in the region. He says health officials want to prevent any outbreak and control “nuisance” mosquitoes that could interfere with recovery efforts.

Van Deusen says FEMA is using modified Air Force C-130 aircraft to spray the chemicals, which he says don’t pose health risks to humans or pets.