Using Herbicides to Treat Invasive Plants: A Tool in the Forest Landowner Management Toolbox – Forestry Research

Invasive plants are defined by the Natural Resources Conservation Service (NRCS) as “a plant that is non-native and capable of establishing on multiple sites, growing rapidly, and disrupting plant communities or ecosystems. Depending on your forest or oak forest terrain, this includes plants such as Scotch broom, sedge, tree of paradise, pampas grass, and Himalayan blackberry. But for forest or oak woodland owners looking to control vegetation, there are also less desirable native plants. NRCS calls these either “incidental native plants or weeds.” Opportunistic native plants, as defined by the NRCS, can take advantage of disturbance to soil or existing vegetation to spread rapidly and out-compete other plants such as mountain ash in the disturbed area. A weed is defined as any plant that is not valued where it grows, such as native plants, or any plant that poses a significant threat to agriculture and/or natural ecosystems, such as Pacific poison oak.

Paradise tree photo with flowers

For any landowner, invasive plant eradication is most effective when infestations are small or localized. When an outbreak covers large areas, you often look to control spread and eradication.

Heather Morrison, Registered Professional Forester (RPF) and Licensed Pest Control Consultant, says, “Often using herbicides in conjunction with other forms of plant management, such as mechanical or burning, increases the effectiveness of the treatment.

We asked Heather about using herbicides to control invasive species and compliment other plant management practices.

Q: Heather, how do you discuss herbicide use with forest owners?

A: I really don’t make it any different from other plant management methods. It is one of the tools we can use and is definitely a big part of IPM (Integrated Pest Management). I offer it as an option and if the landowners have doubts, we will talk about it. Herbicide is not always a good choice, and every situation is different.

Q: What are some examples of the effective use of herbicides as a forest management tool?

A: One of the best uses is in shaded fuel breaks. Maintenance is key! People always seem to forget that the forest does not change and will grow back, so the huge investments we make in establishing these oil breaks can be lost if we don’t take care of them.

Another example is suppressing invasive plants. Wildfires are creating an environment for more invasive plants to spread, such as broom, pepperwood and stinkweed. For the last two years I have been working with some forest owners in the Glass Fire footprint to suppress French broom that was bad before the fire and now it is worse. Because new plants take 2-3 years to produce viable seed, it’s been a race to try and treat these areas before they release too much seed. Broom plants produce thousands of seeds per plant, which last in the soil for 70+ years!

scotch eraser

Photo of scotch tape with flowers

Q: Are there any situations where you don’t recommend using herbicides?

A: Obviously if you are an organic farmer! I usually find that you should change the types of herbicides you use and the method of application. I like to remind you that herbicides are highly regulated and we usually only apply in ounces per acre. This compares to similar herbicides found on shelves where consumers do not read the label, wear personal protective equipment (PPE) or apply the herbicide correctly.

Please note, the US Forest Service’s “Forest Management Handbook” recommends that forest owners needing to apply herbicides to areas larger than 1/10 acre should consult with an RPF, Certified Pesticide Applicator, or Licensed Pesticide Control Consultant.

For more information on integrated pest management and invasive plant identification, please visit the UC IPM website.

To read our interview with heather and herbicide application safety, as well as information about other mechanical and physical invasive plant management methods, download the Forest Management Education Newsletter June 2022.

Download the UC Forest Stewardship Series to learn more about forest conservation, plant management, and forest pests.

Pacific poison oak with fruit

Photo of Pacific poison oak with berries

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