Noxious Weeds
Carol Randall
USDA Forest Service Forest Entomologist
What is a Weed?
• “A plant out of place.”
• “A plant whose virtues have not yet been
discovered.”
• “Plants obstructing the activities of man.”
• “A plant not valued for use or beauty,
growing wild and rank, & regarded as
cumbering the ground or hindering the
growth of superior vegetation.”
Noxious vs. Obnoxious
Weeds
• Noxious weeds are
designated by a regulatory
agency- and by law
managers must manage
these plants
• Obnoxious weeds are
plants which can invade a
site, but which are not
considered enough of a
threat to merit regulation
Why Manage
Noxious Weeds?
Noxious weeds have the potential to:
•
•
•
•
Destroy wildlife habitat.
Reduce recreation opportunities.
Displace threatened and endangered species.
Reduce plant and animal diversity.
• Disrupt waterfowl and migratory
bird flight patterns and nesting
habitats.
• Cost millions of dollars in
treatment and loss of productivity to
private land owners.
"Noxious weed" means any
plant having the potential to
cause injury to public health,
crops, livestock, land or other
property; and which is
designated as noxious by the
director. (Idaho Code 22-2402)
• Have to be designated by law
• Director of the Idaho State
Department of Agriculture
makes legal designation for
Idaho
• Idaho currently has 64
“noxious” weeds
ISDA Criteria for Designating
Noxious Weeds
• It must be present in but
not native to Idaho
• It must be potentially
more harmful than
beneficial to Idaho
• Eradication must be
economically and
physically feasible
• The potential adverse
impact of the weed must
exceed the cost of control
Three Levels of ConcernIdaho’s Noxious Weed List
• Statewide Early
Detection Rapid
Response (EDRR)
List
• Statewide Control List
• Statewide
Containment List
Brazilian Elodea, Giant Knotweed, Canada Thistle
Statewide Early Detection
Rapid Response (EDRR) List
• Theoretically these plants are
not well established in Idaho
• Focus is to identify populations
of these weeds and eradicate
them
• "Eradication" means the
elimination of a noxious weed
based on absence as
determined by a visual
inspection by the control
authority during the current
growing season
European Frogbit
Policeman’s Helmet
Idaho’s Statewide EDRR List (15)
Common Name
Brazilian Elodea
Common/European
Frogbit
Fanwort
Feathered Mosquito Fern
Scientific Name
Egeria densa
Hydrcharis morsus-ranae
Cobomba caroliniana
Azolla pinnata
*Heracleum
Giant Hogweed
mantegazzianum
Giant Salvinia
Salvinia molesta
Hydrilla
Hydrilla verticillata
Policeman's Helmet
*Impatiens glandulifera
Squarrose Knapweed
*Centaurea triumfetti
Syrian Beancaper
*Zygophyllum fabago
Tall Hawkweed
*Hieracium piloselloides
Myriophyllum
Variable-Leaf-Milfoil
heterophyllum
Water Chestnut
Trapa natans
Yellow Devil Hawkweed *Hieracium glomeratum
Yellow Floating Heart
Nymphoides pelata
Statewide Control List
• "Control" means any
or all of the following:
prevention,
rehabilitation,
eradication or modified
treatments
Buffalobur
Dyer’s Woad
Mediterranean Sage
Statewide Control List (22)
Common Name
Scientific Name
Common Name
Scientific Name
Black Henbane
*Hyoscyamus niger
Meadow Knapweed *Centaurea debeauxii
Bohemian Knotweed
*Polygonum bohemicum
Mediterranean Sage *Salvia aethiopis
Buffalobur
*Solanum rostratum
Musk Thistle
*Crupina vulgaris
*Hieracium
Orange Hawkweed aurantiacum
Common Reed
(Phragmites)
*Phragmites australis
Myriophyllum
Parrotfeather Milfoil aquaticum
Dyer's Woad
*Isatis Tinctoria
Perennial Sowthistle *Sonchus arvensis
Eurasian Watermilfoil
Myriophyllum spicatum
Russian Knapweed
Giant Knotweed
*Polygonum sachalinense Scotch Broom
*Cytisus scoparius
Japanese Knotweed
*Polygonum cuspidatum
Small Bugloss
*Anchusa arvensis
Johnsongrass
*Sorghum halepense
Vipers Bugloss
Matgrass
*Nardus stricta
Yellow Hawkweed
*Echium vulgare
*Hieracium
caespitosum
Common Crupina
*Carduus nutans
*Acroptilon repens
Statewide Containment List (27)
• "Containment"
means halting the
spread of a weed
infestation beyond
specified boundaries
Poison Hemlock
White Bryony
Spotted Knapweed
Yellow Flag Iris
Statewide Containment List (27)
Common Name
Scientific Name
Common Name
Scientific Name
Canada Thistle
*Cirsium arvense
Poison Hemlock
*Conium maculatum
Curlyleaf Pondweed
Puncturevine
*Tribulus terrestris
Dalmatian Toadflax
Potamogeton crispus
*Linaria dalmatica ssp.
dalmatica
Purple Loosestrife
*Lythrum salicaria
Diffuse Knapweed
*Centaurea diffusa
Rush Skeletonweed
*Chondrilla juncea
Field Bindweed
*Convolvulus arvensis
Saltcedar
Flowering Rush
Butomus umbelltus
Scotch Thistle
*Tamarix sp.
*Onopordum
acanthium
Hoary Alyssum
*Berteroa incana
Spotted Knapweed
*Centaurea stoebe
Houndstongue
*Cynoglossum officinale
Tansy Ragwort
*Senecio jacobaea
Jointed Goatgrass
*Aegilpos cylindrica
White Bryony
*Bryonia alba
Leafy Spurge
*Euphorbia esula
Whitetop
*Cardaria draba
Milium
*Milium vernale
Yellow Flag Iris
*Iris psudocorus
Oxeye Daisy
*Leucanthemum vulgare
Yellow Starthistle
*Centaurea solstitialis
Yellow Toadflax
*Linaria vulgaris
Perennial Pepperweed *Lepidium latifolium
Plumeless Thistle
*Carduus acanthoides
Something you probably did
not know about Idaho…
We are one of the most
progressive states in the nation
when it comes to addressing
noxious weeds
Idaho’s Statewide Weed Education
and Advocacy Groups
• Idaho Association of Weed Control
Superintendents (IAWCS)
• Idaho Weed Coordinating Committee
(IWCC)
• Idaho Weed Control Association (IWCA)
• Idaho Weed Awareness Campaign
(IWAC)
Other Assets:
• Weed Science Program at the University
of Idaho
• Research Programs at other State
Institutes of Higher Education
• Cooperative Weed Management Areas
Cooperative Weed
Management Areas (CWMA)
Most of Idaho’s land mass is
contained in one of 32 Cooperative
Weed Management Areas (CWMA)
CWMAs are formed when the
landowners and land managers of
a given area come together and
agree to work cooperatively to
control weeds
CWMAs identify the highest priority
weed control activities for their area,
then share resources to get priority
work done
So why is an entomologist
talking about weeds?
• I work closely with county weed
superintendents, CWMA’s, and weed
researchers on classical weed biological
control- or the use of insects to help
control weeds
Idaho- A Biological Control of
Weeds Super Power
• We have weed biological control
researchers at our land grant college
• We have a statewide biological control
coordinator (ISDA/BLM)
• We have designed and implemented the
only statewide biological control of weeds
monitoring program
• We have a number of statewide groups
which cooperate on biological control of
weed projects
How do you develop a weed
treatment strategy
• Most successful weed management strategies
incorporate a number of methods: herbicides,
mechanical, cultural, and when appropriate
biological control.
• Use of multiple methods simultaneously is called
Integrated Pest Management- or IPM.
• A good weed treatment strategy relies on
realistic management objectives, accurate weed
identification and mapping, as well as post
treatment monitoring. (“DID IT WORK?”)
Weed Biocontrol and other Control
Methods
Chemical Control
- Picloram (Tordon)
- 2,4-D
- Glyphosate
- Dicamba
IPM
Biological Control
- insects
- pathogens
Cultural Control
- grazing
(sheep, goats)
- hand-pulling, tilling
- burning
What is Biological Control of
Weeds?
• The use of one organism to control
another.
• Classical Biological Control is the
introduction of control agents- usually
insects- into a region that is not part of their
natural range, to suppress permanently the
populations of selected target weeds
usually also introduced into that region
SUPPRESS not GET RID OF!
Mostly geared towards containment list
How Biological Control Works
• Biocontrol agents may control weeds by
destroying seeds, root, or stems; by weakening
or stressing the weed; and/or by limiting the
weeds ability to reproduce.
• Bioagent feeding may also help secondary
pathogens infect weeds through damage scars.
• Once established and feeding in your weed
infestations, biological control agents will
continue to attack your weeds, month after
month, year after year.
Biocontrol population density
Lesser knapweed flower weevil
Initial release
Lag
time
Establishment of
biocontrol agents
Exponential increase
Larinus minutus
Biological Control Agent Outbreaks
May Control Weed Infestations
Beverly Bridge, AB
Biomass g/m²
180
Leafy Spurge
Grass
150
120
90
60
Aphthona
nigriscutis
30
Leafy Spurge
0
1988
1990
1992
Year
1994
Aphthona flea beetles for
leafy spurge
• Biocontrol agents behave like insect pest
species
• Mass outbreaks
Biological Control Basics:
Advantages
Disadvantages
Target specificity
Continuous action
Initial high costs
Protracted time until
impact likely
Long-term cost effective
Uncertainty over ultimate
scale of impact
Gradual in effect, generally Uncertain ‘non-target’
environmentally benign
effects in ecosystems
Self dispersing (even into
difficult terrain)
Irreversible
Things to Know:
Efficiency of agents cannot be
be be be be guaranteed.
 Will not work every time in
every situation.
 Will not “eradicate” the weed.
 May not provide the desired
level of control.
 Some times it might take
awhile (years) before see
biological control impact.
