Linda R. McMahanOSU Extension Service

Presented at Gardeners Mini-College, Corvallis OR 2010

Note: Some material on control methods developed by and borrowed from retired OSU Extension Professor

Susan Aldrich-Markham

Understanding Invasive Plants

Question 1Of the following plants, which is considered to be an

invasive species in Oregon?1. Salal

2. Purple loosestrife 3. Red maple 4. Ajuga

Question 2Of the following plants, which are considered to be an

invasive species in the United Kingdom?1. Rhododendron ponticum2. skunk cabbage3. Cotoneaster4. All of the above

Interesting Fact: An activity known as “Rhodie-bashing” has become common in England.

Question 3You can best tell if a garden plant is possibly invasive by ?

1. How fast it grows 2. Whether it self-seeds 3. How aggressive it is in your garden 4. Observing it growing in nearby natural areas

What is an invasive plant species? It is one that:1. Spread aggressively, replacing native vegetation2. Seems particularly adept at surviving and

reproducing in wild areas3. Is extremely difficult to control and eradicate4. Leads to economic or environmental harm5. All of the above

Question 4

Question 5True or False:

Invasive species are considered to be the number 1 threat to biological diversity in natural areas in the U.S.

Question 6Invasive plants are spreading over approximately how many

acres per year of US wildlife habitat

1. 500,000 acres2. 1.2 million acres3. 1.7 million acres4. 3.5 million acres

Question 7Estimates of economic damage annually from invasive

plants in the US is measured in:

1. Hundreds of thousands of dollars2. Millions of dollars3. Billions of dollars

Rubus armeniaca, Himalayan or Armenian blackberry

Question 8Can you name this invasive plant occurring throughout

Oregon and the West?

Question 9Can you name this invasive plant in Willamette Valley

oak woodlands?

Daphne laureola, spurge laurel

Question 10What percentage of invasive species in the US have been

introduced through horticulture and gardening?

1. 10%2. 30%3. 50%4. 75%

I am not talking about dandelions!

I am talking about plants whose populations explode in wild areas

Garlic mustard

Like knotweed, here seen on Oregon’s Nehalem River, which was rapidly invaded throughout much of the drainage in the late 1990s and early 2000s.

As gardeners, we have all been part of the problem because many invasive plants are garden escapees, but we can also be part of the solution. Some examples follow.

Ornamental horticulture has been recognized as the main pathway for plant invasions worldwide. We examined the link between . . . pressure created by the presence of ornamental plants in the market and their ability to escape from cultivation and establish in the wild. . . Species that had escaped from cultivation were more frequently on sale both in the nineteenth century and today than nonescaping species. . . (Abstract Excerpt)

Katherina Dehnen-Schmutz, Julia Touza, Charles Perrings, and Mark Williamson. 2006. The Horticultural Trade and Ornamental Plant Invasions in Britain, Conservation Biology 21(1):224-231

Butterfly bush

English Ivy

Yellow Flag Iris

Purple Loosestrife

Herb Robert

Scot’s Broom

http://blogs.oregonstate.edu/h2onc/tag/invasive-species/

Characteristics of Invasive Plants

Lack natural enemiesNon-nativeFast growingFast reproduction and effective dispersalLong-lived seedsFew habitat restrictions Able to form single-species stands

4,000 or more plant species are

introduced into the US, 1 in 10 have become invasive, and half of these are of horticultural origin

The Magnitude of the Problem in the United States

How Did They Get Here?Intentional planting for ornamental value, forage,

or cropsSeed mixes that often contain plants with

invasive potential or unintended weed seedsWeed seeds as contaminants in bird seed and

seed for crops and gardensAs hitchhikers on tires, wheels, boots & shoes,

other plants, & ships

Photo – knotweed infestation in Lincoln Co.

Oregon Department of Agriculture

Knotweed infestation in Lincoln County, OR

Photo – knotweed infestation in Clackamas Co.

Japanese Knotweed(Polygonum cuspidatum)

The Nature Conservancy

Knotweed infestation in Clackamas County, OR

Some Sample Control Methods to Show How Difficult It Can Be

ControllingHimalayan Blackberry as Example 1

Mechanical Control of Blackberry

Cut or mow the canes back to ground level repeatedly

Dig up roots and crowns

Graze with goats (only if desirable plants are not present)

Establish other plants on the site for competition

Chemical Control of Blackberry

Foliar Application

Triclopyr (2-3% solution) apply anytime during active growth period – spring to fall

Or triclopyr ester (4% solution) is effective in the winter, when many native plants are dormant

Or glyphosate (2-3%) fall application only

Chemical Control of Blackberry

Cut Stem Treatment

Apply undiluted triclopyr to freshly-cut stems (be sure to get both ends if rooted)

Not as effective as a foliar application, but does not injure plants growing nearby

Good as a follow-up treatment after most of the blackberry infestation is removed and other plants are established

Blackberry IWM for Large Areas

Option 1 – Cut or mow early to mid-season, allow to regrow grow to about 18 inches tall, then apply herbicide

Option 2 – Broadcast herbicide late summer or fall before cutting or burning

Plant native vegetation to occupy the site

Control competing vegetation around the desirable plants with regular maintenance

Controlling Knotweed

These methods make controlling blackberry look positive easy!

Photo – knotweed infesting the upper Skykomish River, WA

Knotweed infesting the Upper Skykomish River, WA

King County Noxious Weed Program

Photo – knotweed leaves, 3 species comparison

Japanese

HimalayanGiant

Seattle Public Utilities

Winter View

Dense growth pattern

Mechanical Control of Knotweed

Cut knotweed stems at least twice a month between April and August, then once a month until the first frost

Keep this up for 2 to 3 years

Dispose of all cut stems and root fragments because they can resprout

Or cover patch loosely with geo-textile, break off stems growing underneath

Geotextile Fabric

Woven Seattle Public Utilities

Non-Woven

Chemical Control of Knotweed

Stem injection Method (for small patches)

Rodeo and Aquamaster have labels

Inject up to 5 ml into the hollow stem about 6 inches above the ground, just below a node (3 ml is adequate)

Or cut off stem and fill hollow with 3-5 ml

Maximum rate is 8 quarts/acre

Chemical Control of Knotweed

Foliar Application Method (The Nature Conservancy)

Triclopyr or glyphosate (3 to 5% solution), plus a non-ionic surfactant

Spraying plants at 3 to 6 ft tall is practical, but flowering stage is most effective

Best to cut or spray in the spring, then spray regrowth again in the fall

Where to Find Out More Information

http://extension.oregonstate.edu/yamhill/sites/default/files/Ivy_Removal_Fact_Sheet.pdf

Fact Sheet on Ivy Removal in a Home Landscape

Ivy on tree trunk before removal

My story. I moved into a new house in May 2008that had (perhaps literally) a ton of ivy. It coveredthe fences to the extent that I couldn’t even openthe gate without removing some of it. Removingenough ivy to open the fence was my first project.Next, I mowed it back to keep it from spreadingfurther into the yard, until the mower decided itdidn’t like that anymore. Then, since we needed some ivy removal pictures at the office, two of us tackled the English ivy on the Douglas fir tree in the back, using the tree lifesaver method similar to that used by the parks department in the City of Portland.English Ivy (Hedera helix) is a European forestthat has become invasive in the US, where it isofficially considered to be invasive by most states.Because it is such an effective ground cover, it has

A collaboration between the City of Portland, Oregon Public Broad-casting, Oregon Assn of Nurseries, Clackamas Community College, OSU Extension Service, and Oregon Sea Grant —Revised Version Coming to you soon!http://extension.oregonstate.edu/catalog/pdf/ec/ec1620.pdf

Revised version summer 2010 will include more alternatives applicable to Oregon’s Eastside

http://blogs.oregonstate.edu/h2onc/files/2009/08/IS4gardeners_draft_7.5.09.pdf

Invasive nonnative plants are a serious subject for gardeners, farmers, the general public, and land managers. Understanding what invasive species are and how to control them are increasingly important issues for gardeners. What is an Invasive Species? Invasive species are non native organisms whose ‐introduction causes, or is likely to cause economic or environmental harm or harm to human health. Human actions are the primary means by which invasive species are introduced and spread. An invasive plant can also be referred to as a noxious weed because it is listed by state or federal law as particularly

Invasive Species: Some Facts for the GardenerRobert Emanuel, Joy Jones and Linda McMahan

http://emerald.npsoregon.org/PDFs/Invas_Orn.pdf

What does the future have in store? This site is a good one to know what to look out for as probably invasive plants—put together by people who work with natural areas and are on the lookout for unusual plants in nature

NPSO Lists species that are considered to be invasive in wild areas but not yet recognized legally as invasive by the ODA – Sample from List Acer platanoides– Norway mapleAesculus hippocastanum– horse chestnut Cotoneaster spp.-- cotoneaster Ligustrum vulgare– common privitLunnaria annua – money plantLychnis coronaria– rose campionMelissa officianalis – lemon balmPrunus laurocerasus – cherry laurelPrunus lusitanica– Portugese laurelPyracantha spp.– firethorn Rosa multiflora– multiflora roseSaponaria officianalis – soapwortViburnum opulus– snowball tree

NPSO Oregon Watch ListAcer pseudoplatanus– sycamore mapleAcanthus mollis– bear’s breechesAjuga reptans– ajuga Alchemilla mollis– lady’s mantleArum italicum– Italian lords and ladies Betula pendula– European birchCentranthus ruber– red valerianGalium odoratum– sweet woodruffKniphophia uvaria– red hot pokerMyosotis scorpioides– forget-me-notVerbena bonariensis– tall verbenaViburnum tinusViola odorata– sweet violet

How to Do Your Own Searches

Complete a web search putting the scientific name in quotation marks and adding “+ invasive”.

For example, a search for the Ponderosa pine would look like [“Pinus ponderosa” + invasive]. This approach will provide various “hits”; many times these are government and nonprofit organizations that provide this kind of information.

How to Do Your Own Searches Or you can go directly to one source from USDA at http://plants.usda.gov/index.html.

Or you can sometimes locate information by typing [invasive species Oregon] or a similar designation into your search engine.

Other good sources are listed on the following few slides.

http://www.nps.gov/plants/alien/index.htm

The Gardener’s ChallengeStop the Spread – don’t share, if in

doubt, don’t plantRemove – in your own garden and

through efforts in your community Tell others – and recommend

alternativesKeep informed – Read GardenSmart

Oregon and tell others about it.

So, you know it is invasive, now what?

The Gardener’s ChallengeSupport nurseries that offer

alternatives to invasive plantsCheck seed packet contents—such as

for “wildflower” mixes” before purchase

Be especially careful with water plants—many are invasive and others are well-known “hitch-hikers”

Watch the ground under your bird feeder

So, you know it is invasive, now what?

Thank you for being

GardenSmart!