Don't overwater your yards -- this increases the risk of West Nile Virus, warns the Contra Costa Mosquito & Vector Control District.
Overwatering has long been a challenge facing mosquito control experts, the district said, explaining that too much water on the land prevents the water from absorbing into the soil and instead provides mosquitoes more places to lay up to 400 eggs at a time.
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, according to the district. 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, said mosquito program supervisor Greg Howard, but outside of the agricultural domain, mosquito populations are plentiful because as homeowners flood their yards to keep landscaping green, the county now faces the same challenges that used to face commercial operations.
"We often find front yards that are streaming excess water into the catch basins, also known as storm drains," Howard said. "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."
Last year, Howard and his team of state-certified mosquito inspectors saw that residential overwatering led to a runoff collected in a detention basin near Heron Park in Brentwood that kept the ponds flooded year-round. As a result, vegetation grew plentiful and provided water for developing mosquitoes. The dense foliage made mosquito control challenging and increased the risk of mosquito-borne illness.
In Heron Park's situation, the district said it continues to work with Brentwood officials, county flood control officials, and property developers to find a way to clear the vegetation. Last year, they used goats to eat the vegetation.
Howard suggests homeowners follow the recommendations from the Lawn & Landscape Watering Schedule from the Contra Costa Water District:
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.
"The fact is, it is possible to keep a beautiful lawn while reducing the risk of mosquitoes. You can do both," Howard said. "Just give the lawn what it needs without giving mosquitoes what they need."
The district also reported 159 West Nile Virus positive mosquito samples reported in California last week, including one from Contra Costa. So far this year, 396 mosquito samples from 18 counties have tested positive.