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Definitions . Control – prevention of spread by removing fruits and limiting vegetative spread Eradicate – to completely remove a species from a location. Topics. Approaches to control Methods of control Mechanical Chemical (types of herbicides, application methods Selected PNW species.

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  • Control – prevention of spread by removing fruits and limiting vegetative spread
  • Eradicate – to completely remove a species from a location
  • Approaches to control
  • Methods of control
    • Mechanical
    • Chemical (types of herbicides, application methods
  • Selected PNW species

Assessing Invasive Species Threats

At the landscape scale it is

necessary to take two approaches

simultaneously and iteratively:

By invasive species

(Scary species)

By spatial distribution of invaders and conservation goals

(Superlative sites)


Two Assessment Approaches

  • Species Based
  • Site Based

Weed Increase Over Time and Control Potential

Local control and management only

Eradication feasible

Eradication unlikely, intense effort required

Eradication simple

Public awareness typically begins

Acres Infested

Control Costs



Scattered locations

Numerous locations

At or near biological potential

Plant absent



A = Alhagi

H = Hydrilla

P = Peganum

From: Rejmanek,M. and M. Pitcairn


study conclusions
Study Conclusions
  • Eradication possible if under 1 hectare
  • 1/3 of infestations between 1 and 100 hectares eradicated
  • ¼ of those between 101 and 1000 eradicated
  • Cost goes up greatly with size
  • SO early detection and rapid response is essential!!!!!

Rejmanek and Pitcairn 2002

bradley method
Bradley Method
  • Work in the least invaded areas first, working towards invaded areas
  • Make minimal disturbance – mulch if you must disturb the soil
  • Let native plant regeneration and your maintenance ability dictate the rate of weed removal – never overclear
manual and mechanical
Manual and Mechanical
  • Hand pulling

-can use volunteers

-good for small infestations

-can have low ecological impact

-need to keep equipment clean

-minimize disturbance! Mulch!

-best for annuals or shallow rooted perennials

manual and mechanical11
Manual and Mechanical
  • Tillage/hoeing
  • Mowing, brush cutting
    • Best for species that don’t coppice
    • “controls” – does not eradicate except through repeated use
    • Girdling – remove cambium (do not use on coppicing species, beware creating a hazard tree!)
    • May need to remove stem fragments
  • Mulching – bark, hay, cardboard

carpet, etc.

  • Flooding/drawdowns
  • Fire
manual or mechanical soil solarization
Manual or MechanicalSoil solarization

- kills tissue if around 113-131 degrees F

clear plastic more likely to heat to this

- soil should be moist

- not as good for rhizomatous species

- may alter soil biology and chemistry

steam or hot water
Steam or Hot Water
  • Hot water breaks

down the

epidermis, the

plant becomes


  • Waipuna now promoting

foam – coconut syrup and


infrared technology
Infrared Technology
  • Heats to 1000oC
  • Bursts cells – stops


  • Not good for deeply

rooted species

  • Can eliminate or encourage invasive plants
  • Can use cattle, goats, sheep, geese, chickens, ducks, etc.
  • Goats eat broadest list of weeds
  • 500 sheep = 4/5 acres/day
  • Need to fence or pen them in
  • May disturb soil, may pass seeds
mechanisms herbicides
Mechanisms - Herbicides
  • Inhibit respiration
    • Arsenic compounds
    • Metallo-organics (also based on arsenics)
    • Phenols
  • Can be very toxic to mammals
mechanisms herbicides18
Mechanisms - Herbicides
  • Auxins – 2,4,D – causes excess cell division and overgrowth, good on broadleaf weeds, non-persisting, low mammalian toxicity

2,4,5,T – better for woody plants >> has dioxin = Agent Orange, causes cancer

  • Common now: Clopyralid (persists in compost), picloram, triclopyr (Garlon, Brush B Gone)
mechanisms herbicides19
Mechanisms - Herbicides
  • Inhibitors of biosynthetic processes
  • Cell division – “pre-emergent”
  • Nucleic acid or protein synthesis inhibitors – “pre-emergent”
  • Glyphosate – non-selective contact herbicide, interrupts an amino acid production pathway not found in animals – “post-emergent,” Rodeo® used for aquatics
  • Added to facilitate mixing, effectiveness, or application of herbicide
  • “Surfactants,” “spreader-sticker”
  • Usually chemically active, but may be termed “inert”
  • Sometimes included, if not, research to find recommended one for what you use
considerations using herbicides
Considerations using Herbicides
  • Non-target species
  • Use best management practices for handling concentrates
  • Follow ALL laws
  • Must post treated areas
  • Carefully assess site conditions, including weather
  • Likely cannot use volunteers
methods of application
Methods of Application
  • Foliar – spot, boom
  • More herbicide

delivered to


  • May need a


methods of application23
Methods of Application
  • Basal bark
  • 6” band 1’ up stem
  • Must mix with

low ester oil

  • Best for smaller


methods of application24
Methods of Application
  • “Hack and squirt”
  • Cut every 2 in or

so of stem

  • Good for small trees

4-5” dia

  • Creates hazard trees!
methods of application25
Methods of Application
  • Cut stump “Cut and dab”
  • Only need to

treat the cambium

  • Apply immediately

after cutting

  • Paintsticks handy
  • May need to reapply
  • Not as good in early spring
methods of application26
Methods of Application
  • Injected into cambium
  • Can be good for some

herbaceous as well as


  • Little human contact with


  • Buy appropriate injectors
reed canary grass phalaris arundinacea
Reed Canary GrassPhalaris arundinacea
  • Rhizomatous grass
  • Mow 5X +/yr
  • Mulches (+ cardboard)
  • Glyphosate (2%)
  • Shading with plantings
atlantic english ivies
Atlantic/English Ivies

H. helix ‘Pittsburg’

Hedera hibernica ‘Hibernica

H. helix ‘Star’

H. helix ‘Baltica’

  • Fast-growing ground cover
  • Remove vertical vines first
  • Pull and wad vines on ground
  • Can use string trimmer followed by glyphosate or triclopyr
japanese knotweed fallopia japonica
Japanese KnotweedFallopia japonica
  • Strongly rhizomatous shrub
  • Very hard to kill
  • 2X/month mowing for

3 years

  • Injection – 5 ml of

100% glyphosate

  • Triclopyr or glyphosate
himalayan blackberry rubus armeniacus
Himalayan blackberryRubus armeniacus
  • Repeated mowing
  • Digging
  • Cut stump, treat

with triclopyr or

triclopyr + 2,4 - D

iris pseudacorus yellow flag iris
Iris pseudacorusYellow flag iris
  • Freshwater aquatic but

drought resistant

  • Seeds and rhizomes
  • Dense thickets along shore
  • Dig by hand or machine
  • Cutting + glyphosate
scotch broom cytisus scoparius
Scotch broom Cytisus scoparius
  • Prairies, grasslands
  • Nitrogen-fixer
  • Pull or cut stump
  • Seeds long lived
herb robert stinky bob geranium robertianum
herb robert, stinky bob Geranium robertianum
  • Herbaceous annual
  • Spreads by explosive seeds
  • May be allelopathic
  • Easy to pull
  • Seeds live 5+ yrs
hedge bindweed calystegium sepium
hedge bindweed Calystegium sepium
  • Older name Convolvulus sepium
  • Fleshy rhizomes 1-2 ft deep
  • Blankets shrubs
  • Likes wetter soils
  • Responds to triclopyr –

pull as much as possible,

mulch, then spray as vines


  • TNC Weed Control Handbook

  • TNC “Stewardship Abstracts”

  • Start with smallest infestations first
  • There are a variety of mechanical and chemical control methods –combinations may provide the best control
  • For PNW invaders there are a number of strategies for control that must be tailored to the biology of the species