Linda R. McMahan OSU 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 1 Of the following plants, which is considered to be an invasive species in Oregon? 1. Salal 2. Purple loosestrife 3. Red maple 4. Ajuga
Question 2 Of the following plants, which are considered to be an invasive species in the United Kingdom? 1. Rhododendron ponticum 2. skunk cabbage 3. Cotoneaster 4. All of the above Interesting Fact: An activity known as “Rhodie-bashing” has become common in England.
Question 3 You 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: Spread aggressively, replacing native vegetation Seems particularly adept at surviving and reproducing in wild areas Is extremely difficult to control and eradicate Leads to economic or environmental harm All of the above Question 4
Question 5 True or False: Invasive species are considered to be the number 1 threat to biological diversity in natural areas in the U.S.
Question 6 Invasive plants are spreading over approximately how many acres per year of US wildlife habitat 500,000 acres 1.2 million acres 1.7 million acres 3.5 million acres
Question 7 Estimates of economic damage annually from invasive plants in the US is measured in: Hundreds of thousands of dollars Millions of dollars Billions of dollars
Rubus armeniaca, Himalayan or Armenian blackberry Question 8 Can you name this invasive plant occurring throughout Oregon and the West?
Question 9 Can you name this invasive plant in Willamette Valley oak woodlands? Daphne laureola, spurge laurel
Question 10 What percentage of invasive species in the US have been introduced through horticulture and gardening? 10% 30% 50% 75%
Garlic mustard I am talking about plants whose populations explode in wild areas
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.
KatherinaDehnen-Schmutz, Julia Touza, Charles Perrings, and Mark Williamson. 2006. The Horticultural Trade and Ornamental Plant Invasions in Britain, Conservation Biology 21(1):224-231 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)
Characteristics of Invasive Plants Lack natural enemies Non-native Fast growing Fast reproduction and effective dispersal Long-lived seeds Few 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 crops Seed mixes that often contain plants with invasive potential or unintended weed seeds Weed seeds as contaminants in bird seed and seed for crops and gardens As 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. The Nature Conservancy Japanese Knotweed(Polygonum cuspidatum) 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 King County Noxious Weed Program Knotweed infesting the Upper Skykomish River, WA
Photo – knotweed leaves, 3 species comparison Japanese Himalayan Giant
Winter View Seattle Public Utilities 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 patchloosely with geo-textile, break off stems growing underneath
Woven Non-Woven Seattle Public Utilities Geotextile Fabric
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
Fact Sheet on Ivy Removal in a Home Landscape My story. I moved into a new house in May 2008 that had (perhaps literally) a ton of ivy. It covered the fences to the extent that I couldn’t even open the gate without removing some of it. Removing enough ivy to open the fence was my first project. Next, I mowed it back to keep it from spreading further into the yard, until the mower decided it didn’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 forest that has become invasive in the US, where it is officially considered to be invasive by most states. Because it is such an effective ground cover, it has Ivy on tree trunk before removal http://extension.oregonstate.edu/yamhill/sites/default/files/Ivy_Removal_Fact_Sheet.pdf
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
Invasive Species: Some Facts for the Gardener Robert Emanuel, Joy Jones and Linda McMahan 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 http://blogs.oregonstate.edu/h2onc/files/2009/08/IS4gardeners_draft_7.5.09.pdf
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 maple Aesculushippocastanum– horse chestnut Cotoneaster spp.-- cotoneaster Ligustrumvulgare– common privit Lunnariaannua– money plant Lychniscoronaria– rose campion Melissa officianalis– lemon balm Prunuslaurocerasus – cherry laurel Prunuslusitanica– Portugese laurel Pyracantha spp.– firethorn Rosa multiflora– multiflora rose Saponariaofficianalis– soapwort Viburnumopulus– snowball tree
NPSO Oregon Watch List Acer pseudoplatanus– sycamore maple Acanthus mollis– bear’s breeches Ajugareptans– ajuga Alchemillamollis– lady’s mantle Arum italicum– Italian lords and ladies Betulapendula– European birch Centranthusruber– red valerian Galiumodoratum– sweet woodruff Kniphophiauvaria– red hot poker Myosotisscorpioides– forget-me-not Verbena bonariensis– tall verbena Viburnumtinus Viola 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.
The Gardener’s Challenge Stop the Spread – don’t share, if in doubt, don’t plant Remove – in your own garden and through efforts in your community Tell others – and recommend alternatives Keep informed – Read GardenSmartOregon and tell others about it. So, you know it is invasive, now what?
The Gardener’s Challenge Support nurseries that offer alternatives to invasive plants Check 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?