Managing Pests with the Environment in Mind

By Patti Bakker and Todd Burley

Seattle Parks and Recreation (SPR) stewards nearly 12% of property in Seattle. As part of this stewardship it is our responsibility to manage these lands and waters in a way that supports both the people that use them and the ecosystems within them. The parks in our system are not all the same. In fact, SPR manages urban forests, coastal tidelands, stream banks, wetlands, meadows, freshwater shorelines, athletic fields, golf courses, playgrounds, and much more. Each of these areas has specific needs and challenges.

One of the greater challenges SPR faces is managing pests in our parks. A pest is anything that can damage a plant, animal, water quality, or human health. Each of our park areas has different pests that require targeted responses. The pests can be plants like Himalayan blackberry or water milfoil, insects like long-horn beetles or European chafers, mammals like rats, or fungi.

SPR is legally required by the Washington State and King County Noxious Weed Control Boards to manage certain plant pest species in our city so as to prevent their spread, reduce public risk, and support native ecosystems. These “noxious weeds” as they are often called can have economically and ecologically damaging impacts to the ecosystems we are trying to care for. For example, water milfoil in our lakes can overwhelm aquatic habitats, reduce habitat for migrating salmon, and make swimming beaches unpleasant and unsafe. English ivy can smother trees and other vegetation, forming a monoculture where only ivy grows and that harbors rat populations.

To manage these usually non-native species responsibly, SPR has utilized a system for decades called Integrated Pest Management (IPM). This strategy is a holistic method that uses many techniques to address specific pest challenges in our urban setting. IPM begins with planning and design as a preventative strategy, moves into using physical methods, then attempts biological controls, and as a last resort uses chemical methods like pesticides. The cycle of IPM doesn’t end there, however, but continues through a cycle of learning to continue to evaluate the needs and options and to shift our practices away from the use of chemical methods

IPM starts with thoughtful design considerations to minimize the potential for pest issues in the future. This includes plant choice, garden bed design, irrigation infrastructure, and more. SPR’s planning team collaborates with our IPM manager and other specialists to ensure sound decisions are made that will reduce the potential for pests as our landscapes grow and mature.

Two volunteers work to clear invasive species in a Seattle park, and remove English Ivy from a tree's base.

With over 485 parks, however, and a century of park development wherein new pests continued to be introduced, SPR manages parks that were not designed with pests in mind. When pest issues arise, the first method employed is physical. Think of English ivy crawling up a Douglas fir tree. Our urban forest restoration team and volunteers cut the ivy vines and clear a ring around the tree. Scotch broom and Himalayan blackberry are managed in our meadows through periodic mowing over many years to prevent their establishment.

Two Seattle Parks staff, a dark skinned man and a light skinned woman, are kneeled down over a hole they dug investigating the turf at a Seattle Parks athletic field for the newly arrived invasive European Chafer beetle that is damaging grass at parks.

Physical methods are not always enough, however, and we often need to look beyond those options. Luckily, nature has provided many biological tools to assist. Recently, European chafers (a type of beetle) have moved into Seattle and are damaging athletic field turf and other grass areas, making them unsafe for play. SPR is employing adjustments to irrigation and mowing height as tools to create an environment that is less hospitable to the chafers, while also trying out a bacteria-based product that controls chafer grubs without the toxicity of other insecticides. We are also piloting a less-toxic rat control method of injecting CO2 into rat burrows to humanely kill these pests without the use of the harmful poisons that enter the food chain and hurt birds of prey and other predators.

A logo of the Bee City USA organization. It reads "Making the World Safer for Pollinators One City at a Time".

Chemical methods are used as a last resort in IPM strategies. When determined to be needed, pesticides are only used by trained pesticide applicators, and always in a specific and targeted fashion. SPR and the City have developed a tiered system that identifies which pesticides are acceptable to use, based on the precautionary principle to do the least harm. Certain pesticides are not allowed or are severely restricted, and all used are specific to the pest they are meant to address, and applied in a manner during a time that reduces the potential for them to spread beyond their intended use. As a Bee City, we are committed to reducing the use of pesticides and supporting native bees and other pollinators.

As part of our IPM strategy, SPR implements a Pesticide-Free Park program, which has identified 22 parks that are completely pesticide free. We also avoid use of any chemicals on all athletic fields and near play areas or picnic sites. In addition, SPR is also using and exploring many innovative methods of pest control such as increased mulching, applying hot foam, and spraying vinegar. We continue to examine and learn new methods of managing pests in our parks and look forward to trying even more new ways to make the ecosystems in our parks safe and healthy for people and our native plants and animals.

Want to learn more? Visit our IPM website, learn natural yard care tips from Seattle Public Utilities, or call the Garden Hotline (206-633-0224). Our partner, the Northwest Center for the Alternative to Pesticides also offers great resources.

Sign up for SPR’s upcoming webinar, “Managing Pests Sustainably” on June 3, 2021 at 1:00 p.m. and speak to experts from SPR, NW Center for Alternatives to Pesticides, and Seattle Tilth.