Overwatering Increases Risk of West Nile Virus

Easy Steps to Keep Lush, Green Lawns, Without Creating Disease Risk

imageOverwatering has long been a challenge facing mosquito control experts. Too much water on the land prevents the water from absorbing into the soil and instead provides mosquitoes ample locations to lay up to 400 eggs at a time. In turn, those mosquitoes become flying, biting adults that can threaten people and animals with West Nile Virus. Overwatering was once a common practice in the agriculture industry, but has changed in recent years. Some farmers now use drip irrigation to maximize water efficiency and minimize mosquito-producing water sources reducing the risk of mosquito-borne illness for workers and nearby residents.

Ironically, the tide has turned, says Greg Howard of the Contra Costa Mosquito & Vector Control District (District). Howard, a mosquito program supervisor, has spent many years working with commercial irrigation operators to decrease the amount of mosquito habitat. But, even outside of the agricultural domain, mosquito populations are plentiful.  Homeowners have taken it upon themselves in recent years to proactively flood their own front and back yards in search of that emerald green landscape. However, the same challenges that faced commercial operations are now facing neighborhoods across Contra Costa County.

"We often find front yards that are streaming excess water into the catch basins, also known as storm drains," says Howard. "The problem is those catch basins are designed to relocate storm water during the winter months and stay dry during the summer. Daily sprinkler water accumulates in the gutters year-round and we continue to find mosquitoes capable of transmitting West Nile virus right under our feet."  

Just last year, Howard and his team of state-certified mosquito inspectors encountered a serious threat to public health, a result of residential overwatering. The runoff collected in a detention basin near Heron Park in Brentwood kept the ponds flooded year-round. As a result, vegetation grew plentiful and provided harborage for developing mosquitoes. The dense foliage made mosquito control very challenging and increased the risk of mosquito-borne illness for the surrounding residents.

In Heron Park's situation, the District continues to work withBrentwood officials, county flood control officials, and property developers to find a way to clear the vegetation. Last year, they used the unique solution of vegetation-devouring goats that allowed mosquito control to resume. When it comes to this year's overflowing water in front and back yards, Howard suggests homeowners follow the recommendations from theLawn & Landscape Watering Schedule from the Contra Costa Water District. Their recommendations include the following:

  • Take special care with clay soil as it needs fewer and shorter cycles to allow water to soak in.
  • Periodically check working sprinklers to make sure they maintain intended coverage.
  • Choose early morning hours to water because it maximizes absorption of the water that can be lost during midday watering or afternoon evaporation.
  • Be mindful that plants located in shade locations typically require 50% less water.
  • Water lawns appropriately. Lawns generally need no more than four days of sprinkler water per week. Please refer to the Contra Costa Water District Brochure for exact times and intervals.   

"The fact is, it is possible to keep a beautiful lawn while reducing the risk of mosquitoes. You can do both.  Just give the lawn what it needs without giving mosquitoes what they need," says Howard.

July, 2013

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