FAQ's About Invasive Plants and Removal

What is an invasive?
How do invasive species get here?
Why are invasive species so successful?
Why eradicate invasives?
What are the impacts on natural areas?
What areas of the watershed are most affected?
What do you use to eradicate the invasives?
Will the herbicides harm the environment?
What precautions are taken?
Why are the sprayers wearing protective clothing?
What can we do about it?
Can I get help removing invasive plants?
How do I identify invasive plants?
How do I report any sightings of invasive plants?
Can we do this by ourselves?
What else can I do?

What is an "invasive plant"?

An invasive plant is a weed that has become established in natural or wildland areas. It is a non-native plant that was introduced into California through human action. (Whereas native plants are the result of natural processes of plant migration and evolution.) An invasive plant is a species that, after being introduced, is capable of spreading into natural areas without further help from humans. Invasive plants vary widely in their ability to occupy native habitats. Some are true invaders and will readily move into any suitable ecosystem. Others - probably the majority - are more colonizing; they are capable of growing in areas that have been disturbed by human or natural causes, but do not succeed in areas currently inhabited by natives.

Although pest plants in natural lands are both invasive and non-native, not all non-native plants are invasive. Luckily, only a small fraction of the thousands of plant species introduced into California have escaped cultivation, and only a small fraction of those have spread into wildlands..

How do invasive species get here?

Humans are generally responsible for the introduction of exotic plants that can become invasive in the new environment. Invasives can come from horticultural activity such as arboretums, botanic gardens and gardeners. Government conservations activities for screening, windbreak, and erosion control, and also to supply food and cover for wildlife are also responsible for a portion of invasive plant introductions. Accidental introductions for example via ship ballast water account for a small portion of invasives. Keep in mind that plants considered native in some areas and transported by humans to other locations take on invasive characteristics in the new environment.

Why are invasive species so successful?

Most species have predators in their natural range that keep their population numbers in check. When new species are introduced, however, they come without their natural predators.
Most invasive species produce copious amounts of seed. This seed is often bird- or wind-dispersed, allowing it to cover great distances in a short period of time.
Some invasives have aggressive root systems that can spread long distances from a single plant. These root systems often grow so densely that they smother the root systems of surrounding vegetation.
Some species produce chemicals in their leaves or root systems which inhibit the growth of other plants around them.
Most invasives cast extremely dense shade beneath which native vegetation can not survive.
Most invasives thrive on disturbed soil, such as that around newly developed land, or along highways.
As our region becomes more fragmented, through development, local habitats become more vulnerable to invasives.

What are the impacts of invasive plants on natural areas?

Invasive plants can rapidly degrade the quality of wildlands by altering natural processes and reducing biodiversity. The most common impact is a change in the biological structure of the site. Changes in the plant communities (groups of species) will generally drive changes in the populations of animal inhabitants. Because native insects seldom feed on non-native pest plants, insect numbers usually diminish. Native bird and reptile populations decline in turn, because insects were their main source of food. Invasive plants may be inedible or undesirable to native herbivores, both small and large. And birds may not be able to build nests in the non-native plants.

Invasive plants can also change the physical environment. In riparian zones (streams and rivers), dense stands of invasive species such as arundo (Arundo donax) and saltcedar (several species of the genus Tamarix) can clog channels and increase the severity of flooding. Invasives may not root as well as natives, resulting in stream embankments washing away easier. Large infestations, such as the 1.3 million acres of saltcedar in river systems of the Southwest, make this much more than a minor or local problem.

Invasive plants can also cause wildfires of increased frequency, intensity, and size. For example, non-native annual grasses such as red brome (Bromus madritensis) have become increasingly dominant in the Mojave Desert, creating carpets of dry fuel that carry fire rapidly across the landscape. The exotic grasses return in higher densities after a fire, increasing susceptibility to future fires. In 1999, Joshua Tree National Park suffered the largest fire on record, burning 14,000 acres of junipers, pinyon pines, and Joshua trees. These slow-growing native perennials do not recover well from the more frequent fires. Although a Joshua tree can live for hundreds of years, once burned, it will take a hundred years for another to take its place.

Invasive plants can also alter nutrient relationships within an ecosystem, which may impact other life in the habitat. Arundo has invaded streamsides throughout southern California. Because arundo doesn't shade the water as well as native willows and cottonwoods, stream temperatures rise. This stimulates algae growth and increases stream acidity. Reproductivity suffers in the native fish and amphibian populations, and a rich streamside ecosystem is lost to a monoculture of arundo. Other exotic plants take up salts from deep in the soil and deposit them on the soil surface, inhibiting the growth of natives that are less salt tolerant.

Why eradicate invasives?

Invasive plants cause erosion, destruction of riparian habitats, siltation of creeks and waterways, loss of native plants and animal and increase the likelihood of flooding and fires. Invasive plants consume inordinate amounts of water depriving natural species of the water they need to survive, crowd out native plants, and disrupt the natural balance of the eco-system.

What areas of the watershed are most affected?

There is nowhere in California that has escaped completely from this problem. Highly populated regions of the state - especially the coastal zones - have had the most problems due to the greater human presence and disturbance of land. Riparian zones including most canyons are sensitive sites often plagued with exotic weed problems. These areas are culturally important to Californians who enjoy the amenity value offered by rivers and streams, not to mention the water provided for residential, agricultural, and commercial use. Unfortunately, invasives like arundo and saltcedar have huge appetites for water, sucking up as much as three times the amount used by native plants!

What do you use to eradicate the invasives?

Early detection followed by quick action is the best way to control invasive plants because it may allow manual removal. Manual removal is preferred over chemical treatment specially when dealing with a small number of invasive plants. Repeated cutting (to the ground) during the growing season is sufficient to suppress many weeds. Pulling out the roots and bulbs may be necessary. Pulling out the invasive weeds is best in Spring when the ground is moist.

When removing any invasive weed, be careful how you handle cuttings. Keep all cuttings out of the water, otherwise you will spread your problem to your downstream neighbors. Small cuttings from some weeds, especially Japanese knotweed and English ivy, can easily sprout into a new plant. Be careful where and how you compost them. With tenacity and patience, it is possible to remove acres of invasive weeds without herbicides. There are numerous success stories.

Chemical controls are usually used for larger populations. If you decide to resort to herbicides, follow the directions and be sure the product is labeled for the specific plants you are trying to eliminate. Keep all herbicides away from water. Use the least amount necessary. More is not better - more is dangerous! Remember also, that different plants respond to herbicides differently at different times of year

The actual process of removal may depend on the size of the infestation, the habitat it is in, the type of species, its reproduction methods, and the time of year. Using biological control i.e. species-specific insects and diseases from the alien plant, insect of animal's country of origin is not always feasible or may lead to the introduction of invasive insects and animals.

Will the herbicides harm the environment?

Rodeo which is the herbicide being used is the best choice for vegetation control. It is a broad-spectrum grass, broadleaf weed and brush control agent that affects the entire plant, roots and all. It is more convenient to use in difficult-to-reach areas than mechanical methods.

What precautions are taken?

Only trained personnel apply the herbicides under strict safety guidelines. Treated areas are posted and where possible closed to public access until they are judged safe for re-entry (or until the herbicide dries or for the minimum period required by the product label, whichever is longer). Posting is not required in most places, but where it is required (usually by local statute), place notices at points of entry or the perimeter of treated areas. Posting notices should include a statement that the area has been or will be treated, name of the herbicide, date of treatment, appropriate precautions to be taken or the date when re-entry is judged to be safe, and a phone number for additional information. Notices are removed after it is judged safe to re-enter the area.

Why are the sprayers wearing protective clothing?

The sprayers wear protective clothing as part of the safety precautions we practice. They wear protective clothing even if it is not required by the State or by the manufacturer. This is done to make sure that the sprayers are not harmed by repeated or prolonged exposure.

What can we do about it?

Areas with intact, highly diverse, or complex systems are more resistant to invasion and dominance by exotic species, so increased protection of areas of natural diversity is one way to defend against species loss to invasives.
The first step is to prevent any additional, potentially invasive introductions, because once they gain a foothold they are costly and time-consuming to control.
Monitoring and early detection of new infestations is imperative. Invasive species outbreaks are most easily controlled when they are small and the plants are young.
If we can not achieve total control or eradication, we must learn to manage invasive species populations to restrict size and spread, and prevent them from establishing new populations.
Finally we must take an active role in returning our native vegetation to areas where invasive species have been eradicated. Removing invasives without restoring our native flora only opens the site up for re-colonization by the invading force. Restoration is usually a necessary feature of invasive species management. We feel it is important to keep the focus on managing the land for biodiversity, and not just against invasive species.
Individuals can consider landscaping with native plants, and inform others of the problem.
Remove invasive plants from your property.
Report invasive plants sigthings see below.

How do I report any sightings of invasive plants?

You can call 760-436-3944 to report sightings of invasive plants or you can report them by using this form to provide us eith exact information regarding the invasive plants. The San Elijo Lagoon Conservancy as part of the Invasive Plant Removal Project has identified over 400 acres of invasive plant within the CHU, twice the number of acres initially identified.

Can I get help removing invasive plants?

Call us and we will visit your property and help you to identify the invasive and provide advice and assistance in eradication. Call today and help us rid our watershed of invasive plants. Call 760-427-2665.

How do I identify invasive plants?

Avoid plants which self-seed and make seedlings which come up in expected places outside your garden. Plants which produce many seeds and just keep coming back even when you try to remove them are also potentially invasive. Do not use weedy volunteers that appear in parks or abandoned lots. If you happen to live adjacent to a canyon, wildlife area or on a watercourse, pay particular attention to what you plant.

The San Diego chapter of the California Native Plant society has a list of native plant alternatives to exotic plants. The Los Angeles chapter of the California Native Plant Society has a list of the invasive plants for our area.
The Natural History Museum article on invasive plants that includes a list of problematic plants.
The California Invasives Plant Council maintains a list of the most invasive plants and lesser known invasive plants which you should avoid as well.
Rod Randall, from The Department of Agriculture (Western Australia), has drawn upon many sources to compile a list of plants observed being invasive around the world. See list.
Download the full color brochure which gives you alternatives to some common invasive plants. Download it here. This brochure was produced by the CWN in conjunction with the California Invasive Plants Council and other San Diego County and Southern California Conservancy groups.

Or check our invasive plant list which features pictures of the most problematic invasive plants in the San Diego area. (Coming Soon, the brochure is going to print.)

Can we do this by ourselves?

Yes you can remove invasive plants from your own property. Early dection and quick action is the best way to remove and control invasive plants. Be patient as some invasive will keep coming back. You will need to continually remove the new plants in order to truly eradicate the invasive from your property. If you have a large infestation, call us and we will visit your property and help you to identify the invasive and provide advice and assistance in eradication. Call 760-427-2665.

What else can I do?

Help by volunteering

There are many ways that you can help protect our native heritage from damage by invasive species. First, fill out that membership form. If you would like to get some exercise in a beautiful natural habitat, inquire about volunteer schedules at a nearby preserve. Bring friends and kids. These events are great fun. You may get the chance to see parts of the preserve not normally open to the public.

Learn about the issues

Pulling out plantsmay surprise those who do not understand that non-native invasive species can decrease the native biodiversity. While preventing invasions from ever happening is the best solution, once a preserve is being degraded by an invasive species, control is necessary. If nothing is done to counter the invasion, then the native animals and plants will suffer displacement, starvation and even death.

Do not transmit invasive species

If you are a boater, clean your boat and equipment thoroughly when transporting it from one site to another.
If you are a hiker, clean the weed seeds out of your socks and shoes between trips. We recommend you throw the seeds in your fireplace if you have one.
Cleaning your car, bike, motorcycle, horses, or other transportation is also a good way to avoid transporting invasive species seeds. Many invaders get a foothold by invading along transportation routes such as roads or trails.
Of course, never intentionally encourage the spread of non-native species. Obey agricultural import laws (such as customs declaration forms when travelling); fruit and vegetables could be carrying tiny but harmful arthropods or fungi, or could become invaders themselves!
Do not release organisms into the wild. Even if your pet fish were native to an area, you should not release it back into the wild if the fish came into contact with other fish---it could be carrying new diseases that could harm wild fish.
Help by wise gardening: Your plants may be creating new populations you do not know about! Most non-native species are fine for your garden; the invasive ones are the species to avoid. You may want to try a native species garden. Many states have native plant societies that have plant sales or lists of plants to try (or avoid). With a native plant garden, you will have a colorful, low maintenance display that will attract birds and other wildlife!
Spread the word, not the weed. Many people still do not know the damage that can be caused by invasive species. Educate your friends and family about the differences between invasive and non-invasive plants. If you see your nursery selling invasive species, tell them about this problem. Most nursery growers are interested in avoiding problem species and will listen to your concerns.
Make sure your dog or cat does not run freely through preserves set aside for natural biodiversity. Ensure that breeding animals do not contribute to the already large population of feral animals that inhabit our wildlands and prey upon native species.