What’s Up With Weeds: March 2014

Prepare for battle

March is the time of the year when we start preparing for the season-long battle against weeds. Like an army preparing for war, we make sure that our forces are ready, our intelligence is good, and our weapons are sharp. In this sense, March feels very much like the eve of battle. On the even of weed wars, I am reminded of a quote from Sun Tzu’s Art of War

“If you know the enemy and know yourself, you need not fear the result of a hundred battles. If you know yourself but not the enemy, for every victory gained you will also suffer a defeat. If you know neither the enemy nor yourself, you will succumb in every battle.”

This quote reminds me to always consider the enemy I am fighting as well as my ability to fight it. When working with weeds, this can’t be overstressed. It is imperative to understand the nature of the weed you are combating. You need to know how it reproduces, what time of year it is most susceptible, and what tactics have been successful in the past. All too often I hear of a landowner struggling with a particular invasive weed, only to learn that they are treating it after it has already set seed, or they are using a method that has been shown to be ineffective. Whether in war or weeds, you first must know your enemy to be successful.

Preparing for Battle

Watch out invasive weeds, we are ready for you!

The other important factor to consider is to know ourselves. With so many different invasive species issues impacting Clackamas County, we don’t have the resources to address them all. We have to think strategically about our efforts and know our own limitations. We try to address these limitations by educating and empowering landowners and land managers, but ultimately we must face our own limitations. We do this by prioritizing our treatments and by knowing how many days we’ll have in the field. We estimate how many suitable treatment days we will have available for each invasive weed, and we consider our ability to influence how we can impact its distribution.

Know your enemy

As a landowner or land manager, you may be curious about how you can better understand the invasive species that you are dealing with. Unfortunately, in many instances you may not even know the identity of a particular invader.

The Clackamas County SWCD WeedWise program can help you identify the invasive species you are combating. Bring a sample into our office in Oregon City and we can do our best to identify it for you. Your local Master Gardeners can also identify unknown plants for you. Once we have your invasive weed identified we’ll have a much better idea what you’re facing. We typically have factsheets and Best Management Practices on hand to help you with your particular invasive weed.

You can also find additional information for a particular invasive species from our partners at Oregon Department of Agriculture, Oregon iMapInvasives, and The Center for Invasives Species and Ecosystem Health. All of these resources offer have a wealth of information regarding invasives species ecology and management.

Know yourself

As a landowner, one useful strategy for dealing with weeds is knowing whether we have the resources to treat a particular invasion. If you have the resources to treat an entire area then, you don’t have to be strategic about your approach.

But if you are dealing with a large infestation, you might consider a technique known as the Bradley Method of Bush Regeneration. This method was developed by a pair of sisters while working to restore 40 acres of land from invasive weeds in Sydney Australia. The technique involves focusing first on quality areas were you have few problems with weeds and invasives. Within these high quality areas, you control all weeds you find with in this area. Once these areas are cleared you then focus on adjacent areas and allow the natural vegetation to recolonize from the adjacent high quality site. You then continue each treatment period following up in areas that you previously managed, spending only the time and resources you have available, and slowly and deliberately work from a core area that you maintain.

This approach offers a several advantages. For example, the Bradley Method:

  • Preserves your quality areas
  • Improves your mildly degraded areas
  • Allows natural regeneration of your system
  • Holds and maintains your restored areas
  • Allows a deliberate and method approach
  • Is calibrated to your resources

Do consider utilizing the Bradley Method of Bush Regeneration, particularly if you find your invasive species issues overwhelming.

Prepare for victory

With the warm days of spring upon us, it is a good feeling to take the time to arm yourself with the tools you need to be successful. Be sure to identify your problem invaders, learn about the ecology and management of those plants, and then weigh your ability to effective manage your invasives. If you don’t have the ability to manage those problem plants effectively, ask for help. Taking the time now for these weed war considerations will help to assure your success in the season ahead…and as Sun Tzu tells us:

“Victorious warriors win first and then go to war, while defeated warriors go to war first and then seek to win.”


Report Weeds!
Early detection is the key

So what is up with Weeds in March?

Grass-like plants

  • Jubata grass (Cortaderia jubata) is an annual shrub that follows the same timeline as Pampas grass. Plants have seeded. Dig up the entire plant.
  • Common reed grass (Phragmites australis) is a grassy perennial. Plants that were emerging in April, May, and June have seeded, dig up any plants and dispose in trash.
  • False brome (Brachypodium sylvaticum) is a perennial grass. Plants have seeded and going dormant. Please [contactweedwise] if you see false brome!

Herbaceous flowering plants

  • Russian knapweed (Acroptilon repens) bolts in May with flowers appearing in June, July, and August. Control can be through handpulling, tilling, mowing, or digging. Root fragments resprout so it’s important to get all of the plant out of the ground.
  • Garlic mustard (Alliaria petiolata)was forming rosettes through the winter and flowers in April and May. Seeds may be present and viable from June through September! You can hand pull plants, although root fragments can resprout. Please [contactweedwise] if you see garlic mustard!
  • Spotted knapweed (Centaurea biebersteinii) follows the same timeline as Diffuse knapweed. Dig up the entire plant (easier when soil is moist in the spring).
  • Purple starthistle (Centaurea calcitrapa) sprout from seed in winter and develop into rosettes in spring. Starthistle plants flower from July to Spetember. Please [contactweedwise] if you see purple starthistle in your area.
  • Meadow knapweed (Centaurea debeauzii) follows the same timeline as Diffuse knapweed. Dig up the entire plant (easier when soil is moist in the spring).
  • Diffuse knapweed (Centaurea diffusa) is a herbaceous perennial. In May, plants bolt. Flowers appear in May, June, and July. Dig up the entire plant (easier when soil is moist in the spring).
  • Yellow starthistle (Centaurea solstittialis) sprout from seed in winter and develop into rosettes in spring. Starthistle plants flower from May to July. Please [contactweedwise] if you see yellow starthistle in your area.
  • Rush skeletonweed (Chondrilla juncea) bolts in April, May, and June. When it flowers in July, it sets seed quickly!
  • Paterson’s curse (Echium plantagineum) emerges in March and April, flowering all summer.
  • Orange hawkweed (Hieracium aurantiacum) can be dug up in March and April. Be sure to get the roots and runners. Flowering occurs in May and June, and can extend later, with flowers and seeds occurring from July through September. More information is available on the Oregon Department of Agriculture’s page about Orange hawkweed. Please [contactweedwise] if you see Orange hawkweed!
  • Yellow-flag iris (Iris pseudacorus) is a herbaceous perennial that emerges in April and flowers in May and June. Seeds are set from July through September
  • Yellow archangel (Lamiastrum galeobdolon) is a herbaceous perennial the grows throughout the winter and flowers from April to June. Seeds are set in July and August.
  • Kudzu (Pueraria lobata) is a vining perennial. Leaves emerge in April, May, and June. Flowers emerge in July. Please [contactweedwise] immediately if you think you have spotted Kudzu in Clackamas County!
  • Lesser celandine (Ranunculus ficaria) is a herbaceous perennial. Rosettes form in January and February, and the plants flower in March. In April, seeds are set. Remove all of the bulblets and tubers.
  • Tansy ragwort (Senecio jacobaea) is a herbaceous biennial. Rosettes form in March and April, and flowers in May, June, and July. If soil is moist, dig up the rosettes. If you remove the plant during flowering, bag the plant so seeds can’t spread.

Shrubby plants

  • Blessed milk thistle (Silybum marianum) overwinter as rosettes that bolt in March, April, and May. The plants flower in June and July. Mow or hand pull before flowers fully develop.
  • Butterfly bush (Buddleia davidii), a tall deciduous shrub, displays new leaves in April, May, and June, but doesn’t generally flower until July and August. Control by digging up the entire plant. Our Weed Wrench might work!
  • Giant hogweed (Heracleum mantegazzianum) is a tall herbaceous perennial. Plants emerge in March and April from winter rosettes, and accelerate in growth in April and May. When the plants flower in June and July, remove the heads and cut off the plant at the base…but be very careful because the sap of this plant is caustic. ODA says this about Giant hogweed: “This plant is a public health hazard. Do not expose bare human skin to the plant or breathe the smoke from fires if it is being burned. The plant exudes a clear watery sap which sensitizes the skin to ultraviolet radiation. Humans often develop severe burns to the affected areas resulting in blistering and painful dermatitis. Blisters can later develop into purplish or blackened scars.” Please [contactweedwise] immediately if you spot this plant!
  • Gorse (Ulex europaeus) is a single to multi-stemmed spiny shrub that buds in February and flowers in March, April, and May. It goes to seed in June and July. Dig up small plants. Please [contactweedwise] if you see gorse!
  • Policeman’s helmet (Impatiens glandulifera) is a herbaceous annual the begins to emerge in April and grows through May. Flowers appear in June and July.
  • Purple loosestrife (Lythrum salicaria) is a herbaceous perennial that emerges in May and June. Flowers begin to appear in July.
  • Scotch thistle (Onopordum acanthium) is a herbaceous biennial that overwinters as rosettes. Flower stalks emerge in June and flowering is in July and August.
  • Spurge laurel (Daphne laureola) is an annual shrub that emerges in March and flowers in April, May, and June. Berries appear in June and July. Dig up as much of the plant and root system as possible. Please [contactweedwise] if you see spurge laurel!
  • Knotweeds include Japanese knotweed (Polygonum cuspidatum), Giant knotweed (Polygonum sachalinense), Himalayan knotweed (Polygonum polystachyum), and hydrid knotweeds began emerging in April. With warmer temperatures, growth accelerates throughout May and June. Flowers emerge in July and August. Mechanical control requires frequent, persistent effort: cut twice each month from April through August. In the fall, additional steps are needed, including cutting and covering the plants. Knotweeds are so persistent that you need to do this repeatedly for five years to achieve control.

Aquatic plants

  • Parrot’s feather (Myriophyllum aquaticum) is a perennial with underground rhizomes that overwinter. Stems emerge in April and May. Flower stalks appear in June and July. Removing the entire plant, including root fragments, is necessary.

Report weeds!

Visit our page on reporting weeds to file a report.

Report Weeds!
Early detection is the key

Photo credit: National Library of Scotland, Flickr Commons. [From the papers of Field Marshal (Earl) Haig (1861-1928).]


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Clackamas SWCD