Exotic Invasive Plants: Integrated Pest Management at Point Reyes National Seashore

At Point Reyes National Seashore (PRNS), chemical treatment of pests is always the method of last resort. PRNS uses an Integrated Pest Management (IPM) approach, in which pesticides are selected only if other methods are unavailable or unfeasible. An IPM approach is used throughout the National Park Service. For invasive plants, methods are designed to minimize the number of return visits and to improve the likelihood of native plant establishment, so that eventually, natural areas will not need manipulation to stay weed-free. Unfortunately, some invasive plants actually spread faster if only manual methods of removal are attempted. Based on the literature, expert consultation, and professional judgment of NPS biologists, without some targeted and judicious use of herbicides, we risk losing populations of rare, endangered, and threatened plants and animals.

The Scotch broom control project is a recent example of PRNS's use of Integrated Pest Management. Scotch broom is a high-priority invasive plant that can form monocultures and crowd out all other native vegetation. It contains chemical compounds that can be toxic to native wildlife and plants and causes changes in soils and hydrology that can be ecosystem-altering. Scotch broom has been treated at PRNS using fire, heavy equipment, and manual tools since the 1990s. Our goal is to treat all known Scotch broom infestations within the park by 2014. With current funding, more than two-thirds of the 171 acres treated have been removed manually or mechanically. To stop this invasion quickly and effectively enough to protect rare species and native plant communities, PRNS staff decided to treat the remaining Scotch broom with herbicides, adhering to the following herbicide use protocols and mitigations:

• All pesticide use must be approved in advance by the NPS regional IPM coordinator.
• In the field, staff use strict limits to ensure application is limited to calm, drier periods, and to minimize run-off and drift.
• We establish no-herbicide buffers around all waterways, even when using herbicides licensed by the Environmental Protection Agency (EPA) for aquatic use.
• Currently we are only using herbicides in the lowest of EPA's three risks levels (based on hazards to humans and domestic animals).
• Herbicides are applied with bottles, brushes, or backpack sprayers directly to individual plants (no aerial broadcasting).
• We adhere strictly to EPA labels, which regulate amount and methods of application.
• Herbicide application occurs only under supervision by NPS personnel who have been trained in safe use of herbicides and who are usually certified by the California Department of Pesticide Regulation.
• We always add dye to herbicides, so treated plants are marked.
• PRNS staff posts informational signs (including the name of herbicides to be used and a description of the project) in treatment locations that visitors are likely to access 24 hours prior to and after treatment. Posting signs earlier is infeasible since treatment dates are very weather-dependent.
• Although currently used herbicide labels generally allow re-entry in a few hours, we post signs advising visitors not to enter the treated area for 24 hours.

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