California drought may be causing shifts in pest behavior

Sep 17, 2015

This summer, the media frequently reported an increase in the density of pests in the home and landscape. The drought has been cited as the cause of these problems. Pest control companies quoted in articles confirm that the demand for their services is much higher this year than in years past.

Many people are asking, “Why are there so many more pests this year than usual?” According to Dr. Andrew Sutherland, the urban Integrated Pest Management Advisor for the San Francisco Bay Area, we are asking the wrong question. “The overall abundance of pests probably hasn't changed and may even have decreased as compared to wet years. The real questions we should be asking are ‘Why are these pests appearing earlier in the year?' and ‘Why are the pests appearing all at once as opposed to throughout the year?'”

Sutherland says that landscape drydown has occurred more rapidly in recent years, so there may have been a more dramatic shift from high moisture to low moisture, making the nuisance pests migrate earlier in the year and in a more concentrated manner.

“This is also the first year we've seen dramatic changes made by residents due to mandated water use restrictions. Areas with frequent irrigation and lush landscapes aren't available this year, so nuisance pests like outdoor cockroaches, ants and rodents are migrating from dry areas to seek moisture.”

In a nutshell, this is why you may see pests in your home, garage or landscape that you haven't seen before. He gives this example,

“Oriental cockroaches are highly dependent on moisture and humidity and not normally found indoors. Outdoors if you have an irrigation control box, leaky hosebib or water meter box, or a French drain system, that's where you'll find them. But if this water supply has been reduced or shut off, this population you didn't even know of (that's existed for years, perhaps) may crawl under doors or into foundation cracks and move indoors in search of water.”

Sutherland advises against relying on perimeter pesticide sprays to treat for nuisance pests since these applications are only effective for a short time and therefore only represent temporary solutions. Instead, Sutherland recommends the using IPM methods, such as exclusion and habitat modification, which provide more long-lasting pest invasion prevention.

To learn more about pests and get details about how to exclude them, visit the UC IPM Home, garden, turf and landscape pests pages. For other advice on pest problems, contact your local UC Cooperative Extension office and speak with the UCCE Master Gardeners. You can also read the article, "Excluding seasonal nuisance pests from structures".