Seattle Parks and Recreation explores creative pest management strategies for invasive beetle

There’s a new kid on the block, and they are tearing up our athletic fields. It isn’t cleats or shovels, or other tools of childhood that are digging up the grass at our fields, however. And it isn’t even the crows, racoons, and other wildlife doing the digging that are the real culprits. Our new neighbor is up to two inches long, wiggly white, and packed full of protein.

A European chafer larvae

Seattle is in the early stages of a European chafer (Amphimallon majale) infestation. These invasive scarab beetles were first spotted in Washington State in 2008 and recently made their way to our region, most likely via cargo at SeaTac. They are now inching north into south Seattle and beyond. The beetles lay their eggs in turf and the larvae that hatch eat the grass roots, weakening the plant. Then animals like crows come to dig them up and get an easy bite of protein, while also tearing up the fields.

Our first step was to learn – from our situation, others who have experience, and from the science. In 2019, we started annual monitoring of European chafer in our fields. This helped to understand the extent of the problem and informs what strategies we can use to address it. What we learned is that moist fields are less attractive to beetles to lay eggs. And we learned that these pests are still in the early stages of the infestation but are expanding their range here in Seattle

Photo credit: Seattle Times. Dewright Brooks and Patti Bakker investigate turf for chafers.

Next, we followed the steps of our Integrated Pest Management (IPM) program. We always look to behavioral changes first – in this case we want to ensure our athletic fields are adequately watered in the coming summer, to provide an environment that is less attractive for egg-laying. SPR uses RainBird smart irrigation systems that use weather data and real-time information to ensure we do so efficiently. We will also ensure our turf is healthy through use of targeted fertilizers. Athletic fields in the Northwest use a sandy soil base to ensure proper drainage, and they require additional nutrients to remain healthy.

Successful IPM programs look to exhaust all other possible control options before utilizing chemical pesticides. In the case of European chafer, there are fortunately biological control options we can employ. We will be testing use of a bacteria-based bio-insecticide aimed at providing grub control equivalent to chemical methods, but without impacts to non-target insects like pollinators. Another biological control that has been known to be used effectively is a certain species of nematode that hunts down the grubs in the soil and can greatly suppress populations.

We are not alone in struggling to manage this new pest, as described in a recent Seattle Times article, Move over murder hornets, there’s a new bug in town – and its coming for your lawn, featuring Washington State University and staff at Seattle Parks and Recreation. We are working with our partners to share knowledge and get the word out to provide property owners the information they need to responsibly manage European chafer using IPM strategies. By working together and learning from each other, we are using the best available science and identifying the most environmentally safe pest management practices to save our athletic fields and have a healthy environment, too.

This article was written by Patti Bakker (Manager – Green Seattle Partnership, Wildlife, IPM) and Todd Burley (Sustainability Advisor). Questions? You can contact Patti Bakker at Patricia.Bakker@seattle.gov.