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The Latest Dirt - July 2022

An Infestation of Cockroaches in the Garden

By Susan Heckly

Client’s question: We have an infestation of cockroaches in our garden. It started 3 or 4 years ago. We would see them on our neighbor’s sidewalk. Starting this year, they are making our garden their home. This is the worst we have seen in our garden. They hide between the crevices of the retaining wall blocks of the veggie garden.

Photo from https://ucanr.edu/blogs/blogcore/postdetail.cfm ?postnum=39062&
Photo from https://ucanr.edu/blogs/blogcore/postdetail.cfm ?postnum=39062&

At first, we did not want to hire an insect terminator because of the chemicals, but I think we need to. I just want to check if I have any other option going the natural way. We have seen many lizards, but cockroaches come out at night. If we hire a terminator, can we still eat our produce after a chemical spray? I would appreciate your advice on this matter. Thank you.

Susan Heckly’s response: Thank you for contacting the UC Master Gardener Program Help Desk with questions about outdoor cockroaches. There are several types of outdoor cockroaches that live in Contra Costa County. They are generally not considered to be pest insects, as they don’t cause problems for gardens. Outdoor cockroaches eat decaying plant material and dead insects, as well as other insects’ poop. Their fecal material, in turn, helps fertilize the garden. Some parasitic wasps feed on cockroaches.

Most cockroaches thrive in moist, humid conditions. Because a garden can harbor numerous areas where moisture can collect, this provides ample habitat for several of the outdoor cockroach species found in the Bay Area. Buckets, watering cans, and containers that may collect irrigation water should be emptied. Also, keep hedges, shrubs, and low-lying plants well-trimmed to improve sunlight penetration and air flow.

A few of the outdoor cockroaches are known to enter buildings, especially in late summer or fall in search of water, but don’t establish themselves as indoor cockroaches. To keep roaches out of your home, make sure all cracks are sealed, install weather stripping on doors and windows, keep doors and windows closed (including the screens), trim shrubbery from around vents and windows, and remove ivy or other groundcover close to the house.

I would not advise hiring a pest control operator to spray for these cockroaches, as that runs the risk of killing many beneficial organisms. Even for indoor pest cockroaches, pesticides alone will not solve a cockroach problem and must be used with extreme care.

As far as whether produce would still be safe to eat after being sprayed with any chemical pesticide, you would need to check with the person doing the spraying to find out what the product is and what the recommendations are for its use around edible plants.

For more information about cockroaches, with photos of the various outdoor species: http://ipm.ucanr.edu/PMG/PESTNOTES/pn7467.html. I hope this information is helpful. Please let us know if you have more questions.