1. Learning objectives
 Understand Nevada weed law and
assist clients in complying with the law
 Use plant biology to design effective
weed management strategies
 Explain the differences between types
of herbicides, and know when to use
which
 Identify 13 common weeds of turf and
landscapes

2. What’s a weed?
Any plant growing where
it’s not wanted.

3. Weed terminology
 A weed is a plant growing where it’s not
wanted
 An invasive weed is one that moves in and
takes over an area
 A noxious weed is a legal definition (NRS
555)

4. What is a “noxious” weed?
“any species of plant which is,
or is likely to be,
•detrimental or
•destructive and
•difficult to control or eradicate”

5. How do weeds become listed as “noxious”?
• Specific weeds are named as
“noxious” in Nevada Law
• In order to be listed, there must be
some hope of controlling or
eradicating the weed

6. The List
At the time that the Department lists a species, it will
also give a rating of A, B, or C. These ratings reflect:
• the Department’s view of the statewide
importance of the noxious weed,
• the likelihood that eradication or control efforts
would be successful, and
• the present distribution of noxious weeds within
the state.
These lists are found in the Nevada Administrative
Code
(NAC 555.010).

7. The Tiers
A Weeds normally limited in distribution throughout
the state; actively excluded from the state and
actively eradicated wherever found; actively
eradicated from nursery stock dealer premises;
control required by the state
B Weeds more widespread throughout the state;
actively excluded where possible, actively eradicated
from nursery stock dealer premises; control required
by the state in areas where populations are not well
established or previously unknown to occur
C Weeds generally widespread throughout the state;
actively eradicated from nursery stock dealer
premises; abatement at the discretion of the state
quarantine officer

8. Examples of A, B and C-listed weeds
A Listed B Listed C Listed
Yellow Diffuse Perennial
starthistle knapweed pepperweed
Dalmatian
Medusahead Puncturevine
toadflax
Leafy spurge Musk thistle Saltcedar

9. NRS CHAPTER 555
INSPECTION AND DESTRUCTION OF
NOXIOUS WEEDS
NRS 555.150
Every land owner or occupier, whether
private, city, county, or federal shall cut,
destroy, or eradicate all noxious weeds.

10. For information on weed law,
contact:
Robert Little
State Weed Specialist
NV Dept. of Agriculture
775-353-3673

11. How weeds grow

12. Dicot (Broadleaf) Monocot (Grass)
•Two true leaves •One seed leaf
•Broad leaves have •Parallel veins
net-like veins •Fibrous roots
•Coarse tap root

13. Taproot
Fibrous root

14. Growth stages: Seedling
 Small in size
 Small root mass
 Thin plant tissues
 Water and nutrient
requirements small
Name this weed!

15. Growth stages: Vegetative/bolting
 Rapid growth
 Rapid uptake of water
and nutrients
 Development of roots,
stems and leaves

16. Growth stages: Seed production
 Develop flowers and fruit
 Energy directed toward
reproduction

17. Growth stage: Maturity
 Top growth slows or stops
 Little movement of water
and nutrients
 Plant ‘dries down’ and drops
seed
 Annual plants die
 Perennial plant tops die in
preparation for regrowth

18. Plant life cycles
 Annual
 One season for all stages of
development
 Produce foliage, flower seeds, then die Yellow starthistle

19. Plant life cycles:
winter annuals vs. summer annuals
Fall moisture
Warm soil

20. Winter annuals Summer annuals
 Mustards  Knotweeds
 Redstem filaree  Lambsquarters
 Bur buttercup  Common purslane
 Cheatgrass  Pigweed
 Hare barley  Puncturevine

21. Plant life cycles
 Biennials
 Require two seasons for
completion of life cycle
 First year: develop roots and
low-growing leaves
 Second year: flowers, sets Musk thistle
seed and matures
 Examples are mullein and
musk thistle

22. Plant life cycles
 Perennials
 Live more than two years
 Will produce foliage, seed,
and reach maturity year
after year Dandelion
 Examples are perennial
pepperweed and Canada
thistle

23. Reproduction
 Annuals and biennials
 seed
 seed bank

24. Reproduction
 Perennials
 Simple - reproduce by seed and pieces of root, such
as dandelions
 Bulbous - produce seed, bulblets and bulbs, such as
wild onion
 Creeping - produce seeds, rhizomes (underground
stems), stolons (above ground stems), or creeping
roots

25. Weeds are symptoms of problems
 Soil is bare
 Soil is disturbed regularly
 Site is not monitored routinely
 Site is not managed well (watering, mowing,
grazing, etc.)
 Contaminated materials are used
 Invasive ornamentals are planted
 Wrong controls are used
 Etc…

26. Creative methods for getting rid of weeds…

27. Integrated Weed Management
 Uses knowledge about how the
ecosystem works to find
environmentally sound solutions to
weed problems.

28. IWM preferred methods
 Select plant materials that are well-
adapted to our climate and growing
conditions so they can compete with
weeds
 Encourage natural controls
 Manage landscapes correctly to reduce
weed problems
 Etc.

29. Steps in using IPM on weeds
 Identify and assess the problem before you
do anything – is it bad enough to warrant
action? Why do you have a problem?
 Use all the tools in your toolbox to
accomplish the desired result while
minimizing undesirable outcomes
 Consider mechanical, cultural, biological
and chemical controls and match them to
plant biology

30. Prevention

31. Preventing invasion and spread of
weeds
 Plant clean, certified weed-free seed
 Avoid spreading weed seeds with manure
 Sanitize your equipment prior to moving
them from one property to another
 Plant and maintain desirable plant species
 Don’t sell or plant invasive or noxious
weed species

32. Preventing invasion and spread of
weeds
 Monitor plant stock for
infestations
 Minimize soil
disturbance and bare
ground
 Apply the appropriate
amount of water
 Avoid driving in weed
infested areas

33. Cultural control
Use land management tools that
make it difficult for weeds to be
successful
The key: nurture healthy,
successful, desirable competitive
vegetation!

34. Why are dandelions growing in this
lawn?

35. Cultural control
 Water management
 Even water distribution
 Good drainage
 Water in early morning
 Schedule irrigation based on plant
needs
 Drip irrigation when appropriate

36. Heavy traffic compacting soil

37. Cultural control
 Aerating
 Increases the activity of soil
microorganisms that decompose
thatch
 Increases water, nutrient and
oxygen movement into the soil
 Improves rooting
 Enhances infiltration of rainfall
or irrigation

38. Cultural control
 Fertilizing
 Only as needed – use soil tests
 Avoid overfertilization
 Even applications

39. Lawn cut too short

40. Cultural control
 Mowing turf
 Mow heights based on species of grass
 Never remove more than about 1/3rd of
the leaf blade
 Never scalp!
 Keep blades sharp
 Clean mower after mowing weeds
 Don’t mow when soil is wet (compacts)

41. Mechanical control
 Hand pulling
 Hoeing
 Bulldozing
 Mowing

42. Burning and flaming
 Burning can promote invaders by
removing competing vegetation
 Penetration into soil is limited;
does not kill perennial roots
 Does not disturb the soil but can
destroy organic matter
 May need burn permit
 Wildfire concerns

43. Mechanical control
 Repeated tillage can help reduce seed
populations – but disturbs the soil!
 Mulching (with or without fabrics) – must
exclude light; organic mulches can serve as
substrates for weed seed germination

44. Solarizing (use clear plastic
during summer months for
maximum affect)

45. Biological control
 Biological control is the use of
one organism to suppress
another
 Can reduce pesticide use
 Agents can be free or purchased
 Can effectively and
economically suppress pests
 Does not eradicate a weed
USDA-ARS

46. Chemical control:
herbicides

47. How do you pick the right method?
 Identify the weed
 Learn its biology:
 Annual
 Biennial
 Perennial
 How does it spread?
UNCE: www.manageNVpests.info
UC Weed Photo Gallery:
http://www.ipm.ucdavis.edu/PMG/weeds_intro.html
Pacific Northwest Weed Management Handbook weed ID:
http://weeds.ippc.orst.edu/pnw/weeds?weeds/id/index.html

48.  Consider mechanical control for
annuals and biennials
 Perennial invasive weeds often
require the use of herbicides for
complete control

49. How do you pick the right method?
 How much is there?
 What are the goals for the site?
 What special site conditions limit what you can
do?
 What will the client allow and pay for?
 How fast do you need results?

50. Herbicides
 Chemical name
 Ex: N-(phosphonomethyl)glycine
 Common name
 Glyphosate
 Brand or trade name
 Roundup, Aquamaster,
Weed-b-Gone, Rodeo, etc.

51. Thirteen steps to follow before using
herbicides:
1. Identify the weeds
2. Determine their life cycle
3. Consider all control alternatives
4. Select the chemical based on
effectiveness, safety, and price

52. Thirteen steps to follow before using
herbicides:
5. Read the label carefully and make sure the
herbicide is labeled for the site
6. Determine the best time to apply the
chemical
7. Is the chemical restricted-use-only?
8. Consider proximity to water, nearby trees or
shrubs, soil composition, tendency to
contaminate water supplies

53. More things to consider!
10. Check the weather
11. Have you read and do you have a copy of the
MSDS?
12. Are you applying the appropriate amount by
the best method?
13. Do you understand all necessary safety
requirements, and have you followed them
carefully? (gloves, hat, eye protection, long
sleeves, long pants, shoes, etc.)

55. HAZARD = Toxicity x Exposure
Risk, or
the The capacity of a
potential pesticide to cause
for injury injury The risk of a
pesticide
contacting or
entering the
body

56. Hazards increase…
 when mixing and
loading the
concentrate
 with a very high single
exposure
 after many exposures
over time

57. How do soil-applied herbicides work?
 Move into plant with the soil water
solution
 Absorption takes place across the cell
walls of the root hairs
 Non-germinating seeds not affected

58. How do foliar-applied herbicides work?
 More difficult than with root absorption
 Plant cuticle is an effective barrier
 Must penetrate cuticle, might need wetting
agent or oil carrier for herbicide
 Need uniform application to cover plant (need
adequate surface area)
 Must remain on plant for 6-12 hours
 Warm humid conditions ideal

59. Herbicide performance: Temperature
90
Temperature (degrees
80
70
60
50
F)
40
30
20
10
0
0 20 40 60 80 100
Days to control

60. Herbicide performance: Humidity
Herbicide Uptake and Humidity
100
80
Humidity %
60
Rate
40
20
0
Herbicide Uptake

61. Using growth stage to time control of
annuals
100
90
80
70
60
50
Percent Control
40
30
20
10
0
Seedling Vegetative Flowering Mature

62. Using growth stage to time control of
biennials
100
90
80
70
60
50 Percent Control
40
30
20
10
0
Seedling Vegetative Vegetative Flowering Mature
Yr 1 Yr 2

63. Using growth stage to time control of
perennials
100
90
80
70
60
50
Percent Control
40
30
20
10
0
Seedling Bud F. Flower Regrowth

64. Selective herbicides
 Used to kill a specific type of weed
 Broadleaf herbicides--- kill/control broadleaf
weeds only i.e. 2,4-D, Curtail, Tordon
 Grass herbicides--- control only grasses in
broadleaf plantings i.e. Poast, Fusilade

65. Nonselective herbicides
 Kills most or all of the vegetation in
the area covered
 May be pre- or post-emergent
chemicals
 Example is Roundup
ALWAYS READ AND FOLLOW THE
LABEL DIRECTIONS!

66. How do herbicides work?
(modes of action)
 Interfere with or disrupt biochemical or
physiological processes in susceptible plants
 Often affect a specific enzyme or reaction
 Ex:
 amino acid synthsis inhibitors –
glyphosate, imazapyr, chlorsulfuron
 growth regulators – 2,4-
D, dicamba, clopyralid, aminopyralid, triclopyr
 Seedling growth inhibitors – trifluralin, dichlobenil

67. Pre-emergent Post-emergent
herbicides herbicides

Applied to soil Must be applied to living
plant tissue
Kills plants as they
germinate and pick up Little or no soil activity
chemical in young roots
Must be watered or tilled in
May have some post-
emergent activity

68. The ideal weed killer…

69. Site of action
Contact Herbicides Systemic Herbicides
 All parts of the plant  Applied to plant tissue
must be covered to kill
 Is translocated through
entire plant
the plant to the roots
 Usually quick acting
 Takes time to work!
 Most often used for
 Used for perennials
annuals

70. 1 drop of a translocated herbicide (2,4-D) placed on a
soybean leaf (left) vs. a contact herbicide (right)

72. Commonly used herbicides
Glyphosate
Non-selective
Systemic
Half life ~47 days
Readily available to
homeowners
But…does not kill all
weeds
Should be applied to
young, actively growing
weeds

73. Commonly used herbicides
2,4-D
Broadleaf selective
Half life ~30 days
Used in weed and feed
type products and for
weed control in lawns
Can damage adjacent
plants if it volatilizes

74. Commonly used herbicides
Mecoprop (MCPP) salt 0.22%
2,4-D salt 0.12%
Dicamba salt 0.05%
Broadleaf selective
Half life ~30 days or less
Used for weed control in
lawns
Can damage adjacent plants
if it volatilizes (especially
dicamba; also mobile in soil)

75. Commonly used herbicides
Trifluralin
Pre-emergence
herbicide
Lasts about 3 months
Applied as a dry
granule and watered in
Must use it BEFORE
seeds sprout

76. Why do pre-emergence herbicides fail?
 Label directions not followed – not
watered in
 Applied at the wrong time – plants
already sprouted or will sprout after
product has broken down (winter vs.
summer annuals)
 Herbicide layer is physically disturbed
 Wrong product used

77. Factors that affect movement of the
herbicide into the leaf
 Maximum kill will be obtained under warm, humid
conditions with adequate soil moisture
 Environment influences both the herbicide uptake
and how the plant is growing

78. Adjuvant types
 Activators (enhance activity)
 Surfactants (nonionic, etc. – most widely used)
 Oil adjuvants (petroleum oil concentrates)
 Utility adjuvants
 Wetting agents (spreaders)
 Dyes
 Drift/foaming control agents
 pH buffers
 Water conditioners
 Etc.

81. Resistence

82. Managing resistence
 Use Mode of Action information
 Avoid using products with the
same mode of action year after
year

84. Pesticide formulations
 When selecting, consider:
Application method
Ease of storage and mixing
Risk when handling
Risk of moving off-target
Cost

85. Pesticide application equipment

86. Granular spreaders
 Drop (gravity) spreaders
 pattern= width of spreader
 uniform coverage or target
area
 Rotary spreaders
 coverage wider than spreader
 overlap required for
uniformity
 drift to nontarget areas

87. Applying granular products
 Fill equipment on paved surface
 Make “header” strips around the property
 Keep material off paved surfaces and out of
flower beds
 Treat property with parallel swaths
 Use correct overlap
 Turn off spreader before header strip

88. Applying granular products
 Keep spreader level
 Walk at consistent pace
 Don’t stop without shutting
off spreader
 Don’t operate backwards
 Application may change

89. Spray equipment
 Traditional spray guns
 Shower head gun
 Large droplets
 Low pressure
 Spray wand
 Spray booms

90. Small-capacity sprayers
 Used for small areas and spot treatments:
 Most are hand sprayers
 Most use compressed air
 May have a wand, gun, small boom
 Tank pressure drops as solution is sprayed
 Minimal agitation -- WPs settle

91. Application techniques
 Apply only the amount needed for the desired
level of control
 Apply only where pests are located
 Don’t allow activities to reduce effectiveness:
 Rain, not watering-in, etc.

92. Steps in reducing pesticide risk
 Choose the right pesticide product and
apply it at the right time
 Read and follow the product label
 Purchase/mix only what you need
 Use the product according to label
directions
 Watch the weather
 Store and dispose of the pesticide properly

93. Weeds in turf
Tall fescue in bluegrass stand

94. Weeds in turf
 Compete with turf for:
 Growing space
 Water
 Nutrients
 Sunlight

95. Weeds are the result of poor
A dense, healthy stand of
turf is the performance,
turfgrass best defense
against weed invasions
not the cause!

96. Weeds and site conditions
 Compacted soil: knotweed, annual bluegrass
 Wet areas: white clover, annual bluegrass
 Heavy wear: spurge, knotweed

97. Steps in a turfgrass IPM program
Turf and pest Select corrective
knowledge action(s) based on:
• Historical data
• Turf and pest life
Monitor turf cycles
regularly • Problem diagnosis
• Factors favoring
pests
• Predetermined
Diagnose
thresholds
problem
Evaluate and record results for Take appropriate
future management decisions corrective action

98. IWM for turfgrass
 Assess site conditions:
 How turf is used
 Amount of shade
 Soil fertility and pH
 Soil compaction
 Drainage
 Presence of excess thatch
 Current management – mowing height
and frequency, aeration, fertilization,
etc.

99. Stresses
Excessive thatch

100. Stresses

101. Survey for weeds
 Find them
 Identify them
 How many are there?
 When do they occur? Certain times
of the year, certain weather, etc.
 How long have they been there?
 What else is going on at the site?

102. Common turf weeds
 Black medic  Dallisgrass
 White clover  Johnsongrass
 Plantains  Quackgrass
 Spotted spurge  Nimblewill
 Common mallow  Yarrow
 Annual poa  Dandelion

103. Control of Annual Weeds
 Prevent seed set
 Monitor and find weeds early in their
development
 Use mechanical and cultural methods
 If herbicides are used, apply to
young, actively growing plants
 Be prepared to deal with pre-existing
seed bank

104. Control of Biennial Weeds
 Prevent seed set
 Use mechanical and cultural
methods
 Dig out rosettes in the first year
 Be prepared to deal with
preexisting seed bank

105. Control of Perennial Weeds
 Must control existing plant as well
as preventing seed set
 Control is made more difficult by
resprouting from roots
 Herbicides are often needed
 Make sure you pick the right
product for the specific weed

106. Control of Perennial Weeds
 Non-selective herbicides kill any
type of susceptible vegetation
treated (Roundup)
 Selective herbicides work on a
category of plants, such as
broadleaf vs. grasses (2,4-
D, Fusilade)

107. Black medic (Medicago lupulina)

108. Black medic (Medicago lupulina)
 Looks like clover; is a
legume
 Usually a summer annual
 Low-growing
 Hairy leaves and stems
 Shallow tap root
 Three leaflets; middle one
is on a stalk (petiole)
 Bright yellow flowers
 Found where soil is
compacted and grass is
thin

109. White clover (Trifolium repens)

110. White clover (Trifolium repens)
 Creeping perennial
 Stems branch and root at the
stem nodes (stolons); mostly
reproduces by seed
 Shallow fibrous roots
 Three leaflets joined at central
point, may have a whitish
crescent at center; hairless
 White to pale pink flowers on
long stalks
 Common in moist, low-fertility
soils

111. Broadleaf plantain (Plantago lanceolata)
 Perennial
 Basal rosette of leaves
 Leaves are egg-shaped
 5 to 7 prominent veins on
underside of leaves
 Flower spikes are leafless
 Shallow, fibrous roots
 Found in compacted, wet soil

112. White clover and broadleaf plantain

113. Buckhorn Plantain (Plantago lanceolata)
 Forms a rosette
 Leaves are long and narrow
 Leaves all grow at the base of the plant and usually
have short hairs
 Leaves have 3 to 5 prominent veins (or ribs)
 Produces several flowering stalks with a dense 1 –
2-inch-long spike of tiny flowers (“donut”)
 Has simple or branched tap root
 More tolerant of drought than broadleaf plantain

114. Spotted spurge (Chamaesyce maculata L.)
 Summer annual
 Grows in flat, dense mats
 Leaves are opposite and
dark green with purple
spots
 Hairy stems and leaves
ooze an irritating sap
when broken
 Stems have pinkish color
 Tiny pinkish flowers in
leaf axils

115. Common mallow (Malva neglecta)

116. Common mallow (Malva neglecta)
Winter annual to
perennial, usually
biennial
Thick tap root
Prostrate spreading
stems
Leaves are lobed
Flowers white to lavender
Fruit resembles cheese
wheel

117. Annual poa (or annual bluegrass, Poa annua)

118. Annual poa (or annual bluegrass, Poa annua)
Cool-season grass
Commonly confused with similar
perennial
Light-green, flattened stems that are
bent at the base
Leaf blades often crinkled part-way
down
Prolific seeder
Shallow roots form weak sod
Found in compacted, moist areas;
tolerates some shade
Look for “boat-shaped” leaf tips that
curve up like the bow of a boat (Poa)

119. How much is too much?
 Depends on aesthetics, how turf will be
used, how much damage the pest can
cause, what client wants
 One dandelion may be too many, while for
a golf course fairway, 5% white clover may
be the threshold
 Try to discourage homeowners from having
completely weed-free monocultures
 Stress the importance of establishing a
reasonable threshold level

120. Apply controls
 Match controls to weed species,
growth stage, threshold levels, etc.
 Spot-treat whenever possible
 Consider safety for the applicator
and the residents/users of the turf
 Nontarget effects? Phytotoxicity?
 Avoid drift and runoff

121. Herbicide damage in turf (not to
mention the applicator!)

122. Monitor and keep records
 How did your controls work?
 Did weather conditions affect
treatment?
 Include date of treatment,
location, product used, rates,
formulations, application method,
etc.

123. Other common
landscape weeds

124. Flixweed (Descurainia sophia L.)
 Stem is erect and
branched
 Grows to 2 feet tall
 Leaves are alternate
and highly
divided/fernlike
 Can be finely hairy to almost smooth
 Flowers are small, pale yellow, in
clusters
 Flower has 4 petals
 Appears early in spring (winter annual)

125. Hare Barley (Hordeum leporinum)
 Grows to 10 inches tall
 Leaf blades are 1/16 to 2/16 inch
wide and smooth to hairy
 Auricles at base of blade are
well-
developed, long, narrow, claspi
ng and paper thin
 Produces a spike ½ to 4 inches
long with awns ¼ to 1 inch long
 Commonly called foxtail

126. Prickly lettuce (Lactuca serriola L.)
 Annual to biennial that
grows 1 to 6 feet tall
 Stems are hollow and
branch into the flowering
structure; can be smooth
or prickly
 Leaves are alternate, lobed
or entire, twisted at the
base and have prickles on
edge and on the lower side
of the pale midrib; leaves
clasp the stem
 Leaves & stems ooze a
milky sap when cut
 Flower heads are yellow
and look like dandelions
 Has a taproot

128. Prostrate knotweed (Polygonum arenastrum)
 Annual to short-lived
perennial
 Grows in a flat, round
shape
 Stems are round, wiry
and are enlarged at
each joint; highly
branched
 Oval leaves are bluish-
green
 White to green or
pinkish flowers are tiny
and appear in the axils
 Does NOT ooze milky
sap when stem is
broken (vs. spurge)
 Tough taproot

129. Redstem Filaree (Erodium cicutarium)
 Spreads to form a
rosette close to ground
 Stems up to 2 feet long
 Lobed leaves are fern-
like and hairy
 5-petaled flowers are
“Storksbill” purplish-pink in clusters
of 2 or more

130. Russian thistle (Salsola tragus L.);
Barbwire Russian thistle (Salsola paulsenii)
 Summer annual
 Commonly called tumbleweed
 Forms a bushy plant that
breaks off and tumbles when
dry, spreading seeds
 Stems usually have red or
purple stripes
 Leaves are alternate; young
leaves are long and look like
pine needles; later leaves are
short and tipped with sharp
spines
 Flowers are tiny, green or
pink/red and have no petals
 Taproot

131. How to submit a sample for ID
 Fresh sample: entire plant when possible, bag it
and bring it to us
 To store a sample: refrigerate or press carefully
 High-quality digital photos

133. Sue Donaldson
University of Nevada Cooperative Extension
775-784-4848
donaldsons@unce.unr.edu