Resources

Introduction

What is the difference between a native and a non-native plant?

• Native plants are those that have evolved in a certain region, ecosystem or habitat without any direct or indirect human influence. They may also be called "indigenous" plants.
• Non-native plants, which may also be called "exotic" or  "introduced," appear in locations through human influence, whether direct or indirect, intentional or unintentional.  In the United States, many invasive plants were brought accidentally in shipments of grains. Russian olive, on the other hand, was intentionally brought to act as windbreaks in agricultural fields. Myrtle spurge and bachelor buttons, both Eurasia, were introduced as a ornamental garden plants and have since escaped into natural and open areas.

What makes a plant invasive?

Invasive plants are aggressive spreaders and/or prolific reproducers, which can adapt to a variety of conditions and have few natural controls in their new habitat.  The animals, birds, insects, and fungi that controlled them in their native habitat are absent.  They are difficult to control or eliminate once established.  In certain situations, such as over-grazed pastures, even native plants can become invasive.

An invasive plant can be native, non-native, or noxious.

• When a population of native (or indigenous) plants becomes too dense, those plants may also be considered invasive, if they have a negative impact on the abundance or health of other populations of plants, insects, birds, or wildlife.
• Non-native plants are those that have been brought into an area by human activity, such as hiking, farming, ranching, or driving vehicles. This often occurs accidentally, but may also occur intentionally before the impact of introducing the new plant is known. This is the case with the Russian olive, myrtle spurge, and bachelor buttons.
• Both native and non-native plants can be considered noxious (a legal term assigned by federal, state, or county governments), if they are known to have a negative impact on agriculture, navigation, fish, wildlife, or public health. About half of all noxious weeds were garden escapees. Early detection and quick response is critical to slow their spread and protect weed-free areas. In Idaho, landowners are legally required to remove noxious plants.

For a homeowner, a weed is any unwanted plant. It can even be a desirable plant that is simply growing in the wrong place.

Why should we care about invasive plants?

The Boise Foothills and River Corridor support a variety of native plants and animals. Such biodiversity is threatened when a non-native plant species come to occupy these ecosystems. Non-native invasive species can alter the complex balance between plants, animals and soil that have adapted over thousands of years. In extreme cases, the ecosystems that once supported this balance can be eliminated by the introduction of non-native invasive species.

Weeds also have a significant economic impact. The damage they do on croplands, rangelands, wilderness and recreation areas, parks, and forests makes some of that land unusable for farming, grazing, logging, tourism, recreation, and housing, reducing the value of those lands. While some of that cost can be recouped through aggressive weed management, this too has steep costs. Studies at Cornell University suggest that the economic impact of invasive plants in the U.S. to be $120 billion a year.

Weed infestations not only impair the quality of the landscape, but they actually increase the frequency and intensity of wildfires! Invasive plants threaten our forests, farms, and recreation areas, as well as our towns and our homes. In summary, they:

• reduce biological diversity by crowding out native plants
• compete with desirable plants for water and native pollinators
• replace complex plant communities with monocultures
• degrade wildlife habitat
• clog streams and encourage flooding
• increase soil erosion
• blanket trails, walkways, lots, and landscapes

In the Boise Foothills, for example, cheatgrass has out-competed several native grasses and has grown into a blanket of grass covering much of the foothills. Cheatgrass burns easily and thrives after wildfire and, therefore, can replace grasses, shrubs and forbs that do not grow back quickly after fire. Our foothills, once supporting the sagebrush-steppe ecosystem, is now an invaded grassland ecosystem in many areas of the Boise Foothills. This shift in ecosystem causes significant changes in the composition, structure, and ecosystem function in our precious, public open space areas and beyond.

Non-native invasive species are often hard to control. They often require a mix of mechanical, chemical and hand removal efforts over several years to become successfully managed or eliminated. It is key to find and eliminate non-native invasive species when they are small, and remove them before they establish and propagate.

A typical non-native invasive plant will have some or all of the following characteristics:

• high seed production
• long-lived seed viability
• hardy, far-reaching rhizomes (spreading roots)
• ability to spread quickly via seed or roots
• aggressive growth
• ability to out-compete native plants
• toxic chemicals that suppress growth of nearby plants (allelopathy)
• tolerance for disturbed or inhospitable growing conditions

These “weedy characteristics” enable invasive plants to spread—like wildfire! A few weeds spring up, then spread to cover huge areas if not stopped quickly. 

So what are some weeds common to our area? To learn more, read more below.

Learn to Identify Invasive Plants

There are many common non-native invasive species in the Boise Foothills. Learn more by clicking each of them below:

• Cheatgrass (Bromus tectorum)
• Medusahead (Taeniatherum caput-medusae)
• Whitetop (Lepidium draba)
• Scotch Thistle (Onopordum acanthium)
• Jointed Goatgrass (Aegilops cylindrica)
• Perennial Pepperweed (Lepidium latifolium)
• Rush Skeletonweed (Chondrilla juncea)
• Bachelor Buttons (Centaurea cyanus)
• Myrtle Spurge (Euphorbia esula)
• Houndstongue (Cynoglossum officinale)
• Poison Hemlock (Conium maculatum)
• Puncture Vine (Tribulus terrestris)
• Prickly Lettuce (Lactuca serriola)
• Tree-of-Heaven (Ailanthus altissima)
• Russian Olive (Elaeagnus angustifolia)
• Shortpod Mustard (Hirschfeldia incana)
• Teasel (Dipsacus fullonum)
• Himalayan Blackberry (Rubus armeniacus)
• False Indigo (Amorpha fruticosa)
• Broom (Cytisus scoparius)
• Black Locust (Robinia pseudoacacia)

Also check out this Field Guide to Plant of the Boise Foothills to learn more about both native and non-native species common to our area.

Want to see all the noxious weeds in Idaho? Check out the University of Idaho Extension guide. Request your own copy here!

Best Practices

Experts in weed eradication recognize five general strategies for controlling invasive plants. These are listed below, along with suggestions for applying these strategies in the home landscape. In addition, you will find specific suggestions explained in more detail in the “Control strategies” section of each Fact Sheet.

Preventive controls stop invasive plants before they can become established.

• Monitor your landscape frequently and regularly. Be diligent and persistent every year, month, and week. Seeds can lurk in the landscape for many years and germinate when you least expect.
• Be sure that any clothes, boots, gloves, and tools used in the landscape are free of mud and seeds.
• Be sure that pets don’t bring home any seeds in their fur or paws.  If a motor vehicle is driven in an area with an invasive plant infestation, perhaps in the forest, be sure that tires are free of mud and seeds.
• Do not allow invasive plants to flower or go to seed!  Get them before they spread. 

Physical (or mechanical) controls kill plants directly or make the environment unsuitable for them.

Removing invasive plants by hand is not an easy job, but with persistence you will be successful over time.  Continuing these techniques can prevent a reinfestation, too.

• Know the plant’s life cycle because it is useful for understanding how to control it.
  • Annuals are easier to remove early in the season before their roots get established.
  • Biennials are easier to remove in their first year of growth, when their rosettes are in their early stages of root development. In their second and final year, they flower, go to seed, and their roots are firmly established.
  • Perennials live for many years and are extremely difficult to control when they are well established. Roots spread far, wide and deep, and can re-grow from small segments left behind in the soil. They can easily persist for many years, and each year their infestation expands to cover more and more territory.
• Remove invasive plants while they’re young, when the job will be easier especially in the spring when soils are moist.
• Remove plants by hand, by gently pulling up, and, if the root resists, by twisting. Try to remove the entire root system if possible.
• Use a clean, sharp hand tool or shovel to dig out invasives. You do not need to dig out the entire taproot. Cut the taproot a few inches below the soil, and check back frequently to be sure the plant has not re-grown. Try a hori hori knife!
• Be very careful to disturb the soil as little as possible. Seeds are more likely to germinate in loose soil, so try not to create a fresh new seed bed for next season's weed crop.
• Clip off perennial vines, like field bindweed, below the soil level so they can’t photosynthesize. Monitor continually for re-growth, and clip again. Repeat often. Digging out perennial vines disturbs the soil too much and encourages re-growth.
• If the plant has no flowers, buds, or seeds, pull or dig it out, and turn it upside down, leaving it on the ground to decompose and nourish the soil, or put it in a compost bin.
• Bag carefully and dispose of any plants that have buds, flowers, or seeds.
• Bag all roots of perennial invasives because they can re-root.
• Use thick mulch to prevent seeds from germinating or to smother seedlings. After weeds have been pulled, a thick layer of mulch can prevent their re-growth. You can get free compost from the City's compost program.
• If necessary, for larger populations, you can use a string trimmer before buds appear, and be sure to check periodically to be sure no plants have re-grown. It is possible to deplete a weed's capacity to grow by forcing it to re-grow constantly. However, this method is not recommended for perennial plants. It can stimulate growth considerably in the perennials’ well-developed root systems.
• For small areas, a thick layer of newspapers or cardboard can be used to smother a severe, dense infestation. This deprives the roots of sunlight, and overheats the plants, and they die. However, any native plants under the layers will also die. You can cover the newspapers or cardboard with mulch to improve the appearance.
• Consider solarizing the soil. This involves placing clear plastic on the soil and heating it with solar radiation to kill weeds. The University of California has an excellent website on soil solarization. See Solarization for Gardens and Landscapes.

Cultural controls promote the growth of desirable species.

They can reduce establishment, reproduction, dispersal, and survival of invasive plants over time.

• Remember from year to year where specific invasive species are located to help make future identifications easier and to spot infestations early. Maybe make a map. Monitor these locations frequently.
• Plant native plants or seeds, or put down a layer of mulch, where invasive species have been removed. Otherwise, invasive plants will find their way back into the bare spaces.
• Prevent new infestations by being sure that any clothes, boots, and gloves used in the landscape are free of mud and seeds. Be sure that pets don't bring home any seeds in their fur or paws. This is very important for annual weeds like cheatgrass and medusahead rye.

Biological control is the use of natural enemies—predators, parasites, pathogens, and competitors—to control pests and their damage.

Since these strategies involve using diseases or insects on very large populations or monocultures, they are generally not appropriate in home landscapes

Chemical control is the use of herbicides to disrupt unwanted plant growth.

It is preferable to avoid herbicides because they are harmful to the environment, including precious pollinators.  However, they may be the best eradication method in certain situations.

• Consider several factors when choosing to use a chemical control, such as the target species, timing of application, and the number of applications required.
• Herbicides can be organic or synthetic chemicals.
• Always read the label carefully before using any herbicide and follow the manufacturer’s instructions exactly.
• Some chemicals require a pesticide applicator license for their use.
• Get expert advice - try Ada County Weed Control.
• Contact your local county extension office for more information on chemical control.

Become a Weed Warrior

Below are 15 things everyone can do in the fight against invasive species.

• Plant only native and non-invasive plants, so you don’t contribute to the problem.
• Become familiar with local invasive species and remove them from your landscape, like myrtle spurge.
• Pull populations before they spread.
• Use the proper techniques for removal; sometimes pulling weeds encourages more seed germination. (Step down any loose soil and replant native species.)
• Keep your vehicles and pets out of weed patches to prevent spreading weed seeds, burs or spines onto your property and surrounding areas. These can cause physical injury to other vehicles, livestock and people
• If you are building a home, ask the builder to disturb as little of the land as possible. Rope off the areas not to be disturbed. Protect native shrubs like sagebrush and bitterbrush from damage, as well perennial bunch grasses!
• If native vegetation is removed from your property, possibly during home construction, re-vegetate with native plants immediately before non-natives can get established.
• Clean hiking boots, camping gear, and off-road vehicles before and after going into a natural area.
• Volunteer for organized efforts to remove and control invasive species. Look for opportunities here with the City of Boise's Weed Warrior program.
• Show your support for work against invasive species by participating in the events like the Boise Goathead Festival!
• Educate your friends about the website and the importance of reducing invasive plants in their home landscape.
• Ask your political representatives to support invasive species eradication.
• Write a letter about invasive species to the newspaper.
• Become a Master Naturalist.
• Join the Idaho Native Plant Society!

Additional References

Open Space Division: City of Boise Open Space Division Page.

Become a Weed Warrior! Help us combat invasive species and support native plants by taking part in planting and weeding events in the Boise Foothills!

Ada County Noxious Weeds Overview: Excellent source of local noxious weed information and policy.

Invasive Species of Idaho: Government run site with up-to-date information on non-native invasive species in Idaho, based out of Boise.

Global Rangelands Resources: More info on the distinction between non-native and non-native invasives, weeds and noxious weeds, legislation, a helpful video titled Plants Out of Place and much more.

National Wildlife Federation: Invasive Species: More info on the impacts and classification of non-native invasive species.

Invasive Plants Atlas of the USA: The Atlas assists users with identification, early detection, prevention and management of invasive plants.

US Dept of Agriculture National Invasive Species Info Center: Designations, identifications and policy/law resources regarding non-native invasive species.

Invasive species information for homeowners