Weeds 2009

Out of the Wilds and Into Your Garden

Gardening with Western L.A. County Native Plants
Project SOUND - 2009
© Project SOUND

Weeds & More
Weeds

C.M. Vadheim and T. Drake
CSUDH & Madrona Marsh Preserve

Madrona Marsh Preserve
September 5th 2009

© Project SOUND

Does this look like your garden?

You’re not alone – weeds
are a perennial concern in
S. California gardens!

http://www.entrepreneurs-journey.com/824/how-i-made-six-figures-in-one-day/ © Project SOUND

What is a weed? (definition)
 Weed: any plant that is growing
at a site where it is not wanted

http://www.progardenbiz.com/wp/weeds-who-they-are-and-what-they-tell-us/
© Project SOUND

Why control weeds? (it’s a war out there!)

 Weeds compete with desirable
plants for:
 Light
 Water
 Nutrients
 Space
 Weeds also provide hiding
places for insects and serve as a
source of plant diseases.
 Weeds can kill a gardener’s
enthusiasm, which can cause
http://www.nature.org/wherewework/northamerica/states/hawaii/ them to abandon the garden;
Game ends – weeds win
projectprofiles/art26290.html

© Project SOUND

Weeds are particularly challenging in W. L.A. County

 No killing frosts or smothering
snow; weeds that are annuals in
many climates are perennial in
ours
 No killing high temperatures
 People water a lot (up to now)
 Lots of weedy plants to spread
their seeds/invade via roots
http://acwm.co.la.ca.us//scripts/wma_4.htm#F  Use of ‘mow & blow’ gardeners –
weeds hitch-hike between
Castor Bean ( Ricinus communis) gardens

© Project SOUND

Where do alien weeds come from?
 Many of California’s noxious
and invasive weeds came from
regions with comparable
climates in the Mediterranean
region, Australia, S. Africa
http://www.grabovrat.com/mapsViews/mapsViews80.html  Others, including many garden
Mediterranean Climate Zones weeds come from nearly all
parts of the globe, including
particularly western and
central Asia, Russia & Europe
 They were introduced through
human activity, both
http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pni74139-2.html accidentally and intentionally,
including by gardeners.
Percentage of invasive plants accidentally or
intentionally introduced to California. © Project SOUND

Weeds tell a story….

 Type of soil – some prefer
certain soil characteristics
 Available light
 Soil nutrient levels (low or
high)
 Watering practices
 Cultivation practices – how
much the soil is disturbed
To know a weed is to
learn about your garden –  And many other things
and to understand how to
combat it!
© Project SOUND

The more you know about your garden’s own weeds, the better you
will be able to deal with them
© Project SOUND

In the garden (and in the operating room),
first do no harm

Your plan to combat weeds should be reasonable and
environmentally friendly
© Project SOUND

Integrated Pest Management (IPM)

 "Optimum combination of control methods
including biological, cultural, mechanical,
physical and/or chemical controls to reduce
pest populations to an economical
acceptable level with as few harmful
effects as possible on the environment and
nontarget organisms."
R.L. Hix,CA Agric. Magazine, 55:4 (2001)

© Project SOUND

The IPM Pyramid – ‘first do no harm’
 Use the least invasive – and
often most effective - means
first:
 Prevention – cultural
practices
 Mechanical Controls
 Naturally occurring
biological controls (native)
 Consider using non-native
biological controls
(herbivores; diseases)
 Use chemical controls
http://www.team.ars.usda.gov/ipm.html

sparingly, as a last resort:
Non-native and chemical controls may
 Naturally occurring elements
have the important drawback of non-  Biologics – chemicals made
specificity – they kill the good species by plants that are toxic to
weeds
along with the bad.
 Non-biologic herbicides
© Project SOUND

An IPM system is designed around six
basic components
1. Set Action Thresholds
 Before taking any pest control action, IPM first sets an action
threshold, a point at which pest populations or environmental
conditions indicate that pest control action must be taken. The level
at which pests will either become an economic threat is critical to
guide future pest control decisions.
2. Monitor and Identify Pests
 Not all insects, weeds, and other living organisms require control.
IPM programs work to monitor for pests and identify them
accurately, so that appropriate control decisions can be made in
conjunction with action thresholds. This monitoring and
identification removes the possibility that pesticides will be used
when they are not really needed or that the wrong kind of pesticide
will be used.
3. Preventive Cultural Practices
 As a first line of pest control, IPM programs work to manage the
crop, lawn, or indoor space to prevent pests from becoming a
threat. These control methods can be very effective and cost-
efficient and present little to no risk to people or the environment.
© Project SOUND

An IPM system is designed around six
basic components
4. Mechanical controls: Should a pest reach an unacceptable level,
mechanical methods are the first options to consider. They
include simple hand-weeding, erecting weed barriers, and tillage
to disrupt breeding.

5. Biological controls: Natural biological processes and materials can
provide control, with minimal environmental impact, and often at
low cost. The main focus here is on promoting beneficial
herbivores that eat target pests. Use of plant pathogens – ones
specific to the weeds of interest - also fits in this category.

6. Chemical controls: Synthetic pesticides are generally only used
as required and often only at specific times in a pests life cycle.
Many of the newer pesticide groups are derived from plants or
naturally occurring substances (e.g.: allelopathic analogues), and
further 'biology-based' or 'ecological' techniques are under
evaluation (particularly for agriculture, forestry applications).

© Project SOUND

applies to weeds as well as other pests

 Set Action Thresholds
 Does your entire yard need to be
weed free? Choose an area and
focus on it.
 Prioritize weeds by invasiveness
 When to take action against
specific weeds
 In general, a smaller weed is easier to
http://www.statuaryplace.com/store/index.php?main_
page=index&cPath=46
remove than a larger one
 In general, you want to remove a weed
before it flowers & sets seed
© Project SOUND

If you can, do a little bit – but do it consistently

Weeding just 15-30 minutes a day is often all that’s needed
© Project SOUND

Monitor and Identify Weeds
 Get to know the ‘weed seasons’ of your
yard:
 Cool-season weeds sprout any time from
fall through spring. They flower in late
spring/early summer. The plant may
disappear during the hot dry summer, but
you’ll see even more of germinating
seedlings the following fall.
http://www.dynamiteexterminators.com/WeedFacts.html

Cool season weed  Examples: Annual Bluegrass, Bermuda
Annual Bluegrass – Poa annua Buttercup; Mustards; Clovers; Cheeseweed
 Warm-season weeds tend to start growing
in the spring and hang around all through
the growing season.
 Examples: Crabgrass; Bermuda Grass; Kikuyu
Grass; Fountain Grass; Spotted Spurge;
Bindweed; Nutsedge;

 Any season – some species grow all year
long in our climate
Warm season weed  Examples: Creeping Woodsorrel (Oxalis) ;
Crabgrass – Digitaria species © Project SOUND

Climate change: long periods of hot
weather during winter rains

Favors growth of many weeds: jump-start on growth season
Example: Panic Veldt Grass - Ehrharta erecta
© Project SOUND

Monitor and Identify Weeds
 Get to know the geography of
your garden’s weeds
 Areas prone to weeds require
special monitoring & early
intervention
 Discovering geographic patterns
may suggest changes in gardening
practices – decreasing water to the
area; increased hand-weeding
frequency; etc.
 Know that wildlife (birds, etc) will
bring seed into your yard. Be extra
vigilant in areas where they eat,
perch etc.
Oxalis/ Creeping Woodsorrel
Oxalis corniculata
© Project SOUND

Each garden is unique: garden weeds in context
 Soil (including previous amendments)
 Light & water
 Gardening practices: tilling, raking,
mulches, ‘top soil’, hired gardener’s
practices
 The age of the garden (or part of the
garden)
 Previous (and current) plants
 Weeds that hitch-hike in with purchased
plants
 Invasive garden plants [ivy; bamboo;
dichondra; etc]
Dichondra  What’s growing nearby:
Dichondra micrantha  Birds bring seeds; seeds blow
(Dichondra repens)  Weeds grow into the yard

We will introduce you to some general principles, strategies and tools
that you can apply to your own situation © Project SOUND

Garden weeds may vary widely from year to year…
 Example: Shepherd’s Purse
(Capsella bursa-pastoris)
 Why?
 Conditions are right for
germination of dormant seeds;
temperature; rainfall
 Seeds survive up to 35 years in
undisturbed soils
 When conditions are right – they
are ready
 New seeds may have been
brought in by gardening practices
 New seeds may have come in
through natural means; wind,
birds, etc.
http://www.plant-identification.co.uk/skye/cruciferae/capsella-bursa-pastoris.htm
© Project SOUND

The Weed IPM plan for your garden – a
work in progress
 Requires observation &
knowledge – specific for
your garden
 Will vary somewhat with:
 Yearly weather conditions
http://www.hoodcountymastergardeners.org/Demo_2006/Demo_Construction.html
 Maturity of plants
 New plants, and other
changes to the garden

 Will be modified based on
your previous experiences
 Suggestion: keep a garden
notebook/journal
© Project SOUND

Identifying weeds
 Proper weed identification may be your
hardest task.
 Flowering and growing patterns are of great
importance as most weeds are classified as
either annual, biennial, or perennial.
 The color, shape, and placement of the flower
on the weed will also aid you in identifying the
weed.
http://www.hear.org/starr/plants/images/image/?q=061205-1921
 Take pictures of the weeds – or collect and
Kikuyu grass press them - as you find them; makes
Pennisetum clandestinum identifying and recognizing weeds much
easier.
 Try to find them on-line, in books or have
them identified by an expert (County
agriculture extension; local weed control
district).
 If “new” or unfamiliar weeds appear, have
them identified quickly and take appropriate
http://www.tropicalgrasslands.asn.au/pastures/kikuyu.htm
control measures if necessary © Project SOUND

Great resources on-line & in books

© Project SOUND

Identifying weeds is key to your weed strategy
 Knowing the ID of a weed will
tell you:
 Growth pattern – annual or
perennial weed

 Cool/warm season weed – when
to look for it
http://www.earthlygarden.com/category/lawnmower-maintenance/

 How it likely enters your garden
– suggests ways to prevent this

 Useful mechanical/physical
controls

 Chemical controls (if needed)

Kikuyu grass is used for lawns © Project SOUND

Preventive Cultural Practices

 The first line of defense against all weeds is
good prevention
 General goals:
 Prevent the introduction of weeds into the garden
 Prevent the spread of weeds in the garden
 Promote the health & vigor of desired species

 ‘An once of prevention is worth a pound of cure’
– simple preventive practices can save you
serious gardening headaches

© Project SOUND

Common Purslane - Portulaca oleracea
 Characteristics:
 Succulent foliage (healthy edible;
probably should be grown as a garden
vegetable)
 Grows in moist areas (usually)
 Summer (warm season); origin - Asia

 Growth form: herbaceous annual

 How it spreads: seeds (> 50,000 per plant;
http://www.ppws.vt.edu/scott/weed_id/porol.htm

stem pieces

 Control Methods:
 Solarization for pre-planting removal.
 Mulch & dry conditions usually prevent it
from establishing
 Easy to pull or hoe, but pieces of stem
can re-root readily, so be sure to remove
http://commons.wikimedia.org/wiki/File:Portulaca_oleracea_stems.jpg them from the garden.
© Project SOUND

Prevention/Cultural Practices – avoidance/
prevention is key
 Avoid introducing new
weeds into the garden:
 Use only weed-free mulch,
topsoil, other amendments (if
any); beware of ‘free’ material
unless you know it will not
contain weeds/weed seeds
 Check new plants to be sure
that weeds are not
‘hitchhiking’ in the pots
 Be sure to not bring weed
seeds into garden on your
clothes, shoes, etc.

http://asimpleyarn.net/category/garden-on-tuesday/

© Project SOUND

Cultural practices: just good old garden
management practices
 Sanitation
 Clean equipment (including
lawnmowers) to prevent spread of
weed seeds/cuttings
 Weed Disposal:
 Annual weeds can be composted if
they are not in seed.

 Place perennial weeds in a garbage
bag, solarize (leave bag in sun) &
http://www.norcalblogs.com/sustainable/2008/10/compost_
clueless.html

dispose of them in green waste.
Note: a ‘hot’ compost bin will kill
some – but not all – weed seeds,  If any weed is a big problem in your
so be cautious garden, think twice before putting it
in the compost pile.

© Project SOUND

Cultural practices: good garden management
 Keep garden plants healthy; help
them to out-compete the weeds
 Plant native plants densely
enough to crowd out weeds
 Choose native plants that:
 Are vigorous growers – will out-
compete the weeds
 Will prevent weeds from growing
by:
 Providing too much shade
 Producing allelopathic chemicals that
either inhibit weed seed germination
or weed growth: examples: Salvias?,
Chamise, Manzanitas, CA Walnut,
Purple Sage – Salvia leucophylla probably other CSS species
© Project SOUND

Physical Prevention – 2nd line of prevention
 Weeds have growth requirements -
like any other plant:
 Water
 Correct amount of light
 Correct temperature
 Appropriate nutrients

 Prevent seed germination & seedling
growth by limiting the weed’s access
to ‘growth requirements’
 Remember: limit any one of these
and you’ll significantly decrease the
ability of a weed to take over your
garden
Black Nightshade - Solanum nigrum
© Project SOUND

Fortunately, weeds need water to germinate
and grow

 Water-wise gardening methods
will limit some weeds, simply by
decreasing available water
 Particularly helpful for shallow-
rooted weeds
 Also useful for ‘weeds of wet
places’ – will not survive in dry
soil
 Use target watering methods –
water only the plants you want
(drip; hose)

 Be patient – first couple of
years, when you need to water
shrubs more, are the worst
Broadleaf Plantain - Plantago major
© Project SOUND

Broadleaf Plantain – Plantago major
 Large leaves from basal rosette; originally
brought from Europe as medicinal plant
 Usually in damp area of garden

 Growth form: herbaceous perennial
 How it spreads: seed
 Crowd out; needs bare soil to germinate, grow
 Decrease water; aerating the lawn will also
help.
http://www.wildflowers-and-  Dig out before they set seed. Be sure to
remove as much of the roots as possible - can
weeds.com/Plant_Families/Plantaginaceae.htm

regrow from any pieces of the fibrous
You can use your knowledge of rootstalk that remain in the soil.
a weed’s growth requirements
to save time and effort  Chemical control -spot-treat with glyphosate
(Roundup), taking care not to get the chemical
on desirable plants.
© Project SOUND

Before planting a new area…prevention
almost always better than control

 Kill weed plants & seeds
 Solarization
 Chemical methods

 Turn the soil as little as
possible – avoid bringing up
buried weed seeds
 Control weeds before
installation – always less work
in the long run
 Be patient – the more
weeds/seeds are removed
before installation, the fewer
http://earthlandscapes.blogspot.com/2008/02/how-to-choose-best-lawn-grass-2.html you’ll have to pull later
Bermuda Grass
Cynodon dactylon © Project SOUND

Understanding seeds: what seeds need to
germinate

 Water – need to ‘re-hydrate’ before
seedling can start to grow
 Light (small seeds, including many
weeds) or dark (larger seeds)
Virgin’s Bower - Clematis ligusticifolia  Correct temperature; may be warm
Native plant – requires cold treatment or cool – and may be a rather narrow
range. In general, weeds tend to
have larger ranges, but many are
‘warm season’ or ‘cool season’ weeds
 Other factors (heat; smoke; cold
pre-treatment, etc): in general,
Oxalis/ Creeping Woodsorrel
weed seeds have few of these – it’s
Oxalis corniculata one of the reasons they are so
Weed – no special requirements successful
© Project SOUND
http://www.ars-grin.gov/npgs/images/sbml/?C=M%3BO=A

Key preventive method: blocking sunlight
so light-requiring seeds can’t germinate

 Mulches
 Organic
 Inorganic
 ‘Weed block’ methods
 Planting natives that will
create shade

© Project SOUND

Why barrier methods work:
several effects
 Block light, preventing seed
germination
 Physically prevent seedling
growth
 Reduce soil temperature –
particularly in spring – delay
emergence
 Increase soil moisture below
the barrier – too much for
some species (seeds &
seedlings rot)
 Decrease moisture above the
barrier – too dry for
germination
 Chemical compounds released
from barriers/ mulch may
inhibit germination and/or kill
seedlings
http://landscaping.about.com/od/weedsdiseases/ss/weed_fabrics_6.htm
© Project SOUND

Plastic weed barrier cloth (weed block) –
is it good for native plant gardens?
Arguments for Arguments against

 Doesn’t stop all weeds from growing
 Stop some weeds seeds  Weeds grow through the holes cut for
from germinating; blocks planting
light & forms physical  Weeds grow through/on top of the
barrier barrier cloth
 Relatively easy to install  Cloth gets clogged over time – becomes
a water barrier
 Can promote stem & root fungal disease
in trees & shrubs; interferes with
proper drainage
 Doesn’t allow groundcover plants to
root – or for successful re-seeding
 Hard to keep from looking unsightly-
even under mulch
 Can’t be used well on slopes or other
uneven terrain
http://homeideas.howstuffworks.com/weeds-and-invasive-plants/weed-barrier-basics.htm © Project SOUND

Physical barriers
have their place

 Weedblock (plastic or other)
 Under pathways
 Under patios, sitting areas
(hardscaped areas)
http://www.ndmnaturescapes.com/freshplanting.htm  Other areas where planting is
not an option

 Other physical barriers (e.g.,
mowing strip, heavy metal or
wood strip set on edge) at shrub
bed/turf interface to prevent
turf and turf weeds from
encroaching into planted beds

You may also choose more eco-friendly barriers © Project SOUND

Eco-friendly ‘weed
block’ choices

 Newspaper (use a good
thickness to block light)
http://blueplanetgardening.com/sm-push-mulch-away.jpg
 Cardboard
 Degradable weed block
materials – most are
paper-based

‘Garden Trail’ weed block © Project SOUND

What kinds of seeds
are susceptible to
‘dark inhibition’?

 annual species that are small-
seeded and have a light
requirement for germination
such as common lambsquarters
‘Garden Trail’ weed block
and pigweeds are sensitive to
surface barriers
 large-seeded annuals and
perennial weeds are relatively
insensitive to the darkness;
however barriers/mulches still
provide mechanical barriers to
seedling growth.

© Project SOUND

Mulch – the best surface physical barrier
for native plant gardens
 Kind of mulch
 Should be appropriate for the native
plants you’ve planted
 Organic (bark, etc) for most local
shrubs/trees
 Inorganic for Coastal Prairie
(wildflowers) and desert plants

 Must be course enough texture to
allow the mulch surface to dry out

 Depth of mulch layer
 Must be deep enough to prevent
Lesson: geography of weeds light from reaching the seeds
suggests that mulch layer may be beneath it.
too thin at the edge
© Project SOUND

IPM plan changes through the life of a garden/bed

Pre-planting: Prevention/removal

Years 1-2: Monitoring & Removal

© Project SOUND
Pre-planting: Prevention/practices

Knowing the life cycle of weeds is key to your plan
 Knowing the ID of a weed will
tell you:
 Growth pattern/life cycle –
annual, biennial or perennial
weed
 Cool/warm season weed – when
to look for it
Annual weed – Gnaphaleum sp.
 How it likely enters your garden
– suggests ways to prevent this
 How it spreads
 Useful mechanical/physical
controls
 Chemical controls (if needed)

Perennial weed - Oxalis pes-caprae
© Project SOUND

Annual, Biennial & Perennial Weeds
Short-lived (fixed)
Spreading
Character Annuals perennials or
perennials
biennials
Vegetative
< 1 year 2 to a few years Long, indefinite
lifespan
Vegetative
No Accidental Yes
reproduction
Seed longevity Years to decades Years to decades A few years
Energy allocated
to seed High Medium high Low
production
Establishment Seeds Seeds Mainly vegetative
Usual means of In soil, manure, Soil, wind, feces,
In soil
dispersal equipment, wind crop seed
Lambsquarters, Quackgrass,
Examples Dandelion
Annual Bluegrass
http://www.css.cornell.edu/weedeco/WeedDatabase/index2.html bindweed
© Project SOUND

Annual weeds  Spread by seed. They may self-seed or
they may be brought into the garden by
wind, water, birds, animals or people.
 The most important way combat annual
weeds to prevent more seeds from
developing. Annual weeds are
phenomenally prodigious seed producers.
 A single crabgrass plant, for example,
can produce 100,000 seeds
 If you don't get rid of these intruders
before they develop viable seeds, the
number of weed plants will increase
every year,
 Examples of annual weeds include:
bindweed, chickweed, crab grass,
knotweed, lambs-quarters, mallow,
pigweed, purslane, speedwell, spurge and
yellow oxalis
 Your strategy: kill before they flower
Annual Sowthistle & set seed
Sonchus oleraceus
© Project SOUND

Annual weeds, ancient wisdom

http://www.backsavergrip.com/photos.htm

http://www.english.illinois.edu/maps/poets/a_f/erdrich/boarding/gallery.htm

 Getting weeds out of the garden at the start of the season,
when they're most vulnerable, is a smart strategy: it is easiest
then & it keeps annual weeds from forming seed heads
© Project SOUND

Puncture vine - Tribulus terrestris
 Sharp, thorny burs
 Grows in dry areas of garden



 Prevent introduction: sanitation

http://www.ppws.vt.edu/scott/weed_id/trbte.htm
 Hoe or dig plants before they can set seed;
cut below the crown to prevent regrowth.

 Chemical control: pre-emergence herbicides
containing trifluralin or pendimethalin may
be used on some lawn grasses and
ornamentals. For post-emergence control in
lawns, use a selective herbicide containing
MCPA, MCPP, and dicamba.
© Project SOUND

Vigilance is the key
 The only way to control annual
weeds is to get rid of them before
they go to seed. Luckily annual
weeds are very often shallow
rooted and can be easily hand
pulled or cut off with a hoe.

 Hopefully you will see less and less
annual weeds as the season goes
along, but new seeds will always
find their way in and some seeds
remain dormant in the soil until
ideal conditions present
themselves and they germinate, so
http://www.frenchgardening.com/aujardin.html?pid=310620990670798
weeding is an ongoing process.

If you get in the habit of doing a little weeding each time you
work in your garden – or even every day - it won’t become an
overwhelming task (this is known as the ‘Bradley Method’.
© Project SOUND

Crabgrass - Digitaria species
 Thrives in hot moist areas – lawns,
flower gardens
 Shallow-rooted

 Growth form: annual grass


 Pull before it sets seed.
 Water deeply, but infrequently; this
tactic will dry out crabgrass roots,
killing the weeds or at least
diminishing their vigor.
 Solarization can control crabgrass if
high temperatures are achieved.
http://www.ppws.vt.edu/scott/weed_id/digis.htm

© Project SOUND

Crabgrass - Digitaria species

 For chemical control in lawns and
around ornamentals, use a pre-
emergence herbicide such as
trifluralin; apply it in late winter to
early spring, depending on when
http://www.ppws.vt.edu/scott/weed_id/digsa.htm
crabgrass germinates in your zone (a
local nursery or your Cooperative
Extension Office can provide this
information). For post-emergence
control around ornamentals, apply
fluazifop-butyl or sethoxydim.

http://www.aragriculture.org/horticulture/ornamentals/weed_id/crabgrass.htm

© Project SOUND

Control methods: mechanical

 Hoeing is by far the easiest
 Draw Hoe - the familiar flat-
bladed hoe works best when pulled.
With a sharp blade, you can make
quick work of the long rows
between vegetable crops.
http://landscaping.about.com/od/weedsdiseases/ss/weed_fab

 Warren Hoe - has a pointed blade
rics_3.htm

heart-shaped blade that is usually
used for creating furrows but also
works well for small weeds and
weeding between rows.
 Scuffle, Stirrup, Hoola or Dutch
Hoe - Cuts weeds at the surface in
a push/pull motion. Easy to use and
nice for covering a larger area.

© Project SOUND


http://landscaping.about.com/od/weedsdiseases/ss/weed_fabrics_3.htm © Project SOUND

 Hand pulling/digging
 Good for small numbers of weeds
 Allows you to get the roots out
(important for some perennial weeds)
 The easiest and most convenient
weeder is your hand.
 It becomes second nature to yank a
weed or two every time you walk
http://homeideas.howstuffworks.com/weeds-and-invasive-
plants/how-to-weed-your-garden-in-spring-and-summer.htm

outdoors.
 Hand pulling is also the best method
for a densely planted garden bed that
has been neglected.

 Wide variety of hand tools – try
them out to see what works best for
you

http://www.sujutools.com/image/gardentool2.jpg © Project SOUND

 The Heart Hoe with its single
Classical weeding tools edge thin blade is for ridding
your garden of unwanted weeds
and roots. It also is handy for
weeding the cracks in the
sidewalk and driveway.

 The Claw is excellent for
cultivating flower beds and
vegetable gardens.
 The Cape Cod Weeder has an
angled blade that removes weeds
below the surface of the soil.
This tool will also handle those
weeds in the cracks of sidewalks
and driveways.

The Weed Slicer (Dutch Hoe) cuts off weeds at the roots with little soil disturbance
The Diamond Hoe has an unique diamond-shaped blade for cultivating soil, dislodging
weeds and roots, or breaking up clumps of dirt.
The Trowel is for digging; The Transplanting Trowel has a narrower blade for precise
digging in any garden. It is very good for tight spaces, planting bulbs or fitting
transplants into a full bed.
The Dandelion Weeder is for getting under weeds with tap roots, like dandelions, and
prying them out.
© Project SOUND
http://yardener.com/YardenersToolshedofProducts/HandTools/HandToolsForLawnCare/HandToolsForWeeding/WeedersbySnowNealley

Spotted Spurge - Chamaesyce (Euphorbia) maculata
 prostrate, often forming dense mats
 Broken stems emit a milky sap

(summer)


 Prevent it’s entry into the garden –
good prevention methods
 Solarization prior to planting to kill
seeds
 Mulching to prevent germination
 Hand pulling
 Only if these fail do you resort to
chemical methods
http://www.aragriculture.org/horticulture/ornamentals/weed_id/spurge_spotted.htm © Project SOUND

Annual Bluegrass - Poa annua
 Bunching grass
 Great seeder

 Growth form: annual grass (cool-season)

 How it spreads: seeds
http://www.aragriculture.org/horticulture/ornamentals/weed_id/bluegrass_a
nnual.htm
 Avoid bringing into garden – particularly
in nursery pots, on equipment, clothing
 Mulch - coarse, thick to block light
 Limit water; Zone 2 or 1-2 – has shallow
roots
 Mechanical weeding – before it seeds
 Chemical methods – often not needed

© Project SOUND

Mechanical/Physical Controls – other
 Flaming
 Done with a high flame temp. torch;
 Plants are not burned but ‘boiled’
 Not very effective with grasses
 Be careful to not ignite mulch
 Foaming –
 Hot-foam and steaming is mainly done
by professionals; cool foams are
available (Weed B Gon & others)
 Good selectivity – can ‘spot kill’
 No fire danger
 Can’t use near water; kills fish

 Boiling water – good for weeds in
pavement

© Project SOUND
http://yardener.com/FlamingWeedTools.html

Mechanical/Physical Controls, cont.
 Mowing/cutting (e.g.,
‘weed-whacking’)
 Good in large areas; better
than nothing
 Ok for annuals prior to
seeding; not so helpful for
perennials
 Tilling
 Keep to a minimum – brings up
new seeds in our climate

 Newer technologies
 Lasers – now being tested in
agriculture

© Project SOUND

Consider buying
some good tools

 If you do a lot of
weeding you’ll grow to
appreciate a good tool –
works well & easier on
http://ergonomics.about.com/od/gardeningequipment/ss/useradtools_7.htm
the body

Radius Garden Weeder

© Project SOUND

What the pro’s like….
 Asparagus knife
 Hori-hori knife
 Fiskars ‘Big Grip Knife’
(~$10)

http://www.fine-tools.com/garten.htm

© Project SOUND

Perennial Weeds
 Live more than a single season.
 Usually reproduce both by seeds
and vegetative reproduction
(underground root systems
(rhizomes) and/or sending out
runners (stollons) aboveground.
 Are the most difficult to get rid of
in the garden.
 Examples include: bindweed,
nutsedges, dandelion, dock, ground
ivy, horsetail, Japanese knotweed,
plantain, poison ivy, Bermuda grass,
etc.
 some weeds that are annuals in
other climates are short-lived
perennials in ours (Ex: Cheeseweed)
© Project SOUND
http://www.zum.de/stueber/lindman/234.jpg

Cheese Weed - Malva neglecta
 long, tough taproot

 Growth form: herbaceous short-lived perennial
(in our climate)

http://jeantosti.com/fleurs3/

 Hoe or pull these weeds when they're young.
 Chemical control:
 pre-emergence herbicide containing isoxaben to
prevent seedlings from becoming established in
lawns and around ornamentals.
 post-emergence control in lawns, use a product
containing MCPA, MCPP, and dicamba.
 Spot-treat young weeds with an herbicide
containing glufosinate-ammonium or lyphosate,
avoiding contact with desirable plants.
© Project SOUND

Some weedy invasive perennial grasses spread via
seed alone

Pampas Grass - Cortaderia selloana
http://www.hotgardens.net/Blooming_Pampas_Grass.JPG

Fountain Grass – Pennisetum setaceum
Mexican Feather Grass – Nassella
(Stipa) tenuisima © Project SOUND

But most have modified roots & stems
that help them to thrive

 Runners (stolons): A well known example of that would be
crabgrass. It spreads with creeping stems that grow along
the ground. Buds along the runners produce plantlets that
root and spread very quickly
 Roots or Rhizomes: Quackgrass would fall into this
category. It has tough, white rhizomes that look like roots
and are very sharp. Weeds that spread by roots or
rhizomes can regrow after being cut back. Even chopped up
pieces of root or rhizome may regrow.
 Bulbs and bulbils: An example of this is a spiky grass called
nutsedge. It has tubers or little bulbs that break off when
you pull the grass therefore never eliminating the
plant. They can pop up over night (again and again and
again...!).

© Project SOUND

Weeding Perennial Weeds
 If you catch them young, perennial weeds can usually be pulled
out of the ground easily.
 Once established, they can be next to impossible to get rid of, as
anyone who has battled Bermuda grass or yellow nutsedge in
flower beds will attest.
 With perennials, it is essential to get all of the plant out of the
ground. When perennial weeds are tender seedlings, they can
usually be pulled up by hand with ease, especially when the soil is
moist. But the more time you allow these weeds to take hold, the
harder they are to eradicate. The least bit of Bermuda grass
rhizome left behind can sprout into a new plant.
 The best time to weed is shortly after a rain or an irrigation
cycle. Hand-pulling is the quickest method. If the weeds don't
yield easily or if they detach from the roots when you pull,
switch to a trowel or dandelion weeder and dig or pry them out.

© Project SOUND

http://www.clintsdandydigger.com/

‘Weed Twister vs. Tree of Heaven
© Project SOUND

Special management strategies for perennials

 Exhaust the roots by
continual cutting/hoeing
 Remove roots/rhizomes
or other reproductive
organs from the soil
http://www.moberlymo.org/index.aspx?NID=232

© Project SOUND

http://pirateneo1.blogspot.com/2009/03/back-soon.html

Burmuda Buttercup : Oxalis pes-caprae

 Hoeing and tilling are not good choices for removing perennial
weeds.
 Hand weeding will work if you are very thorough about getting
the whole plant and root system.
 Sometimes herbicides are the only solution for eradicating
tough perennial weeds like poison ivy, ground ivy and brambles.
© Project SOUND

Yellow (Creeping) Woodsorrel - Oxalis corniculata
 Very aggressive invader
 Sun or shade

 Growth form: herbaceous perennial with
fleshy taproot

 How it spreads: seed (propelled to 6 ft);
shallow, spreading root system

 Dig out small plants before they set
seed.
 Water deeply but infrequently

© Project SOUND

Yellow (Creeping) Woodsorrel - Oxalis corniculata


 For chemical control, use a pre-
emergence herbicide containing
oryzalin or pendimethalin to
prevent seeds from germinating
and becoming established. Spot-
treat oxalis in garden areas with
glyphosate, taking care to avoid
contact with desirable plants

http://www.ipm.ucdavis.edu/PMG/WEEDS/creeping_woodsorrel.html

© Project SOUND

Biological controls
 The use of plant-feeding insects, pathogens, or diseases that are host-
specific to a noxious or invasive weed species, with the intention of
suppressing the weed’s population to an acceptable level.
 Biological control does not intend to eradicate the target weed species, but
instead is used to bring the plant into balance with the rest of the landscape.
It is important to note that successful biological control agents are specific to
the plant they are intended to control. In other words, the biological control
agent feeds and develops only on the intended weed species. Therefore, the
risk to other plants and organisms in the ecosystem is minimal.
 Examples:
 Large herbivores: sheep, goats
 Weed-specific pests (insects)
 Example: releasing weevils that eat the seed of musk thistle; Releasing an insect whose
larvae eat the roots of the weed.
-Releasing a round worm (nematode) or a mite that causes a gall (swelling) on the plant.
-Infecting the weeds with specific fungi that damage that weed.
 Potential problems: loss of specificity; toxicity of other control methods to the insects
 Weed-specific diseases
 Example: Puccinia rust can be used to control nutsedge
 Lots of interest/research but not much application to garden yet

© Project SOUND

Chemical controls
 Non-biologics
 Vinegar mixed with a little dish soap
 Non-selective – don’t get it on things
you want
 Works best on young weeds
 Salt – best for weeds in pavement

http://www.housenumbers.ca/weeds.html  Biologics
 Example: AAL-Toxin (isolated from
the pathogenic fungi, Alternaria a
lternata f. sp. lycopersici ) - Highly
susceptible species include such
important agricultural weeds as black
nightshade

© Project SOUND

Control methods: ‘Safe Organic’ pre-
emergents with corn gluten meal
 ‘Safer ‘Concern’ - Contains corn gluten meal (84%) and
sulfate (16%)
 Application Recommendations:Apply 10-20 lbs. per 1000
square feet in the Spring & Fall for pre-emergent
protection. Weed Prevention Plus is granulated and easy to
apply with a spreader or you can apply with the 5 lb. shaker
bag to small garden areas. Homogenous pellet provides
uniform nutrient and herbicide distribution. This product can
also be applied as a regular nitrogen fertilizer in the Summer.
 Recommended for the control of curlydock, purslane, clover,
dandelions, crabgrass and many other common weeds. Proper
application provides up to 90% effective weed control in the
first year for dandelions and crabgrass. Safe for children,
pets and wildlife immediately after application. Can be applied
at any time without burning. Water thoroughly after
application then allow to dry for 2-3 days.

http://www.organic-gardening-shop.com/Agorganics/Product_Details.aspx?ProductID=120
© Project SOUND

Some pesticide definitions
 Preemergence Herbicides
 Preemergence herbicides affect germinating seeds.
 To be effective, the herbicide should be applied two to three weeks
before weed seeds germinate.
 Consequently, preemergence herbicides are most effective against
annual weeds.
 Postemergence Herbicides
 Postemergence herbicides are used to kill weeds after the weed
plants are up and growing.
 To be effective, most postemergence herbicides must be absorbed
through the leaves; consequently, liquid sprays generally work better
than dry, granular materials.
 Postemergence herbicides are most effectively applied when weeds
are young and growing vigorously.
 For some weeds, repeated application at 20–30 day intervals may be
required for control.
© Project SOUND

Some pesticide definitions
 Selective postemergence herbicides
 are usually used to control annual,
biennial, and perennial broad-leaved
weeds because they will kill many
broadleaf plants without damaging
grass plants.
 There are also selective herbicides
that kill only grasses
 Nonselective postemergence
herbicides
 kill all plants, both desirable and
undesirable.
 These herbicides can be used to spot
treat perennial grassy weeds that
are not affected by selective
herbicides.
 To spot treat an area, thoroughly wet
the weed foliage with herbicide
solution.

http://www.dgsgardening.btinternet.co.uk/weedremoval.htm
© Project SOUND

How do herbicides work

 Pre-emergent

 Post-emergent
 Block key chemical pathways in the plant: plant
hormones; chemicals needed for photosynthesis
 Inhibit basic cell functions: cell division;
production of key chemicals

© Project SOUND

Herbicides: pre-emergent

 Last 6-12 months

http://www.ctmpest.com/weedPreventionAndControl.htm

http://www.viewpoints.com/Preen-Garden-Weed-Preventer-review-166f1 © Project SOUND

Yellow nutsedge - Cyperus esculentus
 Looks like a sedge
 Grows in moist areas

 Growth form: perennial sedge (summer)

 How it spreads: seed; tubers (nutlets) from
roots

 Remove when young ― < 6 inches tall. Older,
taller plants are mature enough to produce
tubers; when you dig or pull the plant, the
tubers remain in the soil to sprout.
 For chemical control, try glyphosate, being
careful not to get the chemical on desirable
plants. It is most effective when the plants
are young; it will not kill tubers that have
become detached from the treated plant
© Project SOUND

Bindweed - Convolvulus arvensis
 Also called wild morning glory, bindweed
grows in open areas usually in loam to clay
soils

 Growth form: perennial vine from deep root

 How it spreads:
 Bindweed is deep rooted, so pulling
usually doesn't eradicate it ― the stems
break off, but the weed returns from the
roots.
 Dig the roots out repeatedly (persistence
is required).
 Prevent seeding: hard-coated seeds can
sprout even after lying dormant in the
soil for 50 years!
© Project SOUND

Bindweed - Convolvulus arvensis
 For chemical control, you can use a pre-
emergence herbicide containing trifluralin
around ornamentals. In midsummer, when
bindweed is at the height of its growth
season but has not yet set seed, spot-treat
isolated patches with glyphosate, taking
care to avoid contact with desirable plants.
If the weed is twined around desirable
plants, detach it before treating. Repeated
applications are usually needed to destroy
the root system.

© Project SOUND

Bermuda Grass - Cynodon dactylon
 A fine-textured and fast-growing
perennial, frequently planted as a lawn

 Growth form: perennial grass (summer)

 How it spreads: spreads by underground
stems (rhizomes), above ground runners
(stolons), and seed.
http://www.aragriculture.org/horticulture/ornamentals/weed_id/bermudagrass.htm

 If you have a Bermuda grass lawn, use
deep barriers or edging to prevent it
from advancing into other parts of the
garden.

© Project SOUND

Bermuda Grass - Cynodon dactylon
 Dig up stray clumps before they form
sod, being sure to remove all the
underground stems; any left behind can
start new shoots. Repeated pulling and
digging are generally necessary to stop
this weed; mulches will slow it down, but
it eventually grows through most of them.
 For chemical control, you can use a
selective herbicide containing fluazifop-
butyl or sethoxydim, which can be
sprayed over some ornamentals. Spot-
treat actively growing Bermuda grass
with glyphosate, taking care not to get
the chemical on desirable plants.
http://www.ipm.ucdavis.edu/PMG/WEEDS/bermudagrass.html

© Project SOUND

Other weedy grasses that spread via
seed and rhizomes

Quack grass - Elytrigia repens Panic Veldt Grass - Ehrharta erecta Kikuyugrass -
Pennisetum clandestinum

© Project SOUND

Safety precautions when using herbicides

 Read and follow all package instructions
 Provide adequate ventilation and wear a respirator,
rubber gloves, goggles, and protective clothing
when handling.
 Remove contaminated clothing and launder prior to
reuse.
 Shower after completing the job.
 Wash hands with soap and water before eating,
smoking, or using the toilet.
 Store in a secure, dry, well-ventilated, separate
room, building or covered area

© Project SOUND

 Most herbicides become less effective when a
plant is under stress. Along with crops, most
weeds are also experiencing water stress under
current conditions. Therefore, you may have to
wait until the soil is fairly moist before applying
any systemic herbicides (e.g., Roundup) to manage
weeds.
 Most systemic herbicides perform better under
conditions that are ideal for weed growth. When
the plants are free of stress, herbicides are
absorbed faster and move better within the plant
system, providing more efficient kill.
© Project SOUND

 Fall is a good time to apply systemic herbicides to manage perennial weeds.
These weeds have perennating organs like rhizomes and stolons that help
them persist year after year. Development of these organs usually occurs
during the early fall. During a drought, it is possible that drought tolerant
perennial weeds are more prevalent in fields than annual weeds. Therefore,
fall may be a good time to apply a systemic herbicide (an herbicide that is
absorbed and moved within the plant tissues). A non-selective systemic
herbicide like glyphosate could be applied as a spot application. Grass killers
(graminicides) like sethoxydim, clethodim or fluazifop may also be applied
during fall to manage perennial grasses.

 The main key to control of perennial weeds is application of glyphosate,
dicamba (Banvel), and/or 2,4-D when they are are in the bud to bloom stage,
or as late in the fall as possible before the weeds senesce or growth ceases
due to frost or freeze. At this growth stage, the weeds will move herbicide
throughout the plant and into the roots, resulting in maximum kill of the
entire plant. The best opportunity for making this type of application is
during the late-summer through fall after wheat harvest when plants have
grown undisturbed for several months.

© Project SOUND

Potential problems with use of herbicides

 Cost
 Herbicide-resistant weeds. The evolution
of "superweeds" capable of resisting
herbicides

© Project SOUND

Summary: Identifying a weed will allow you
to choose the best strategy to prevent its
spread
 Annual weeds – reproductive strategy: seeds
 Key – prevent seed production

 Biennial/non-spreading weeds – reproductive strategy: seeds
 Removal (mechanical best) – hopefully when young (year 1)
 Prevent seed production – year 2

 Perennial weeds – reproductive strategy: seeds, vegetative
 Removal – hopefully when young (year 1)
 Prevent seed production and/or other primary means of
reproduction
 May need to use chemical controls – but only after other means
are exhausted
 Use UC IPC website for up-to-date management
recommendations

© Project SOUND

Advice from pros: The ABC’s of Weeding
 Learn how the weeds spread (root
system or seed dispersal) to
understand when and how to handle
them.
 Keep cultivation/tilling to a minimum
 Get the weeds early before they
flower and go to seed.
 Get ‘em while they’re small.
http://walkinggodsway.blogspot.com/2008/06/taught-
through-image-today.html
 Frequent, short weeding sessions are
the best way to stay on top of
Repetition is the key to weeds. Not only does this eliminate a
combating persistent weeds. long, tiring weeding session, it also
Even tough weeds such as lets you dispatch weeds while they’re
bindweed and kikuyu grass can still small and easy to eliminate.
be brought under control with  Weed wet. Weeding goes faster and
careful and fastidious weeding easier when the soil is moist than
practices. when the soil is dry
© Project SOUND

What is a noxious weed?

 Invasive alien plant: an invasive
unwanted non-native plant
 According to The Flora of North
America, the most comprehensive
reference on this continent's plants,
one-fifth to one-third of all species
growing north of Mexico have come
from other continents.
 Noxious weed: any species of
plant which is, or is likely to be,
detrimental or destructive and
difficult to control or eradicate
 We are located in the Los Angeles
Weed Management area – report
noxious weed infestations to them
http://www.co.chelan.wa.us/nw/nw_weed_photos.htm © Project SOUND

Comparison of common weedy plants
and invasive plants.
Agricultural or garden weeds Invasive plants
Introduction Usually accidental by people, Can be accidental, but more often
animals, equipment, or seed the original intention was for
contamination. ornamental or aquarium use, or for
forage, food, fiber, medicinal, or soil
stabilization purposes.

Disturbance Require human disturbance to Benefit from human disturbance, but
establish and persist. disturbance not required.
Persistence Will not persist without human Once introduced, plants survive and
disturbance, usually soil tillage or spread on their own without further
irrigation. human assistance.

Life form Primarily terrestrial annuals or All growth forms, including aquatic,
herbaceous perennial species. climbing vines, parasitic,
herbaceous, or woody plants. Can
have annual, biennial, or perennial
life cycles.

http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn74139.html
© Project SOUND

In natural areas (and in your garden ecosystem),
noxious weeds impact native ecosystems by:
 Reducing biodiversity
 Altering hydrologic (water) & soil
conditions
 Altering fire intensity and
frequency
http://faculty.jsd.claremont.edu/dthomson/studentres.htm

 Modifying successional pathways
 Competing for pollinators
 Displacing rare plant species

 Replacing complex communities
with simple communities
http://www.nps.gov/hafo/naturescience/grasses.htm

Cheat Grass – Bromus tectorum © Project SOUND

Characteristics of invasive plants: general

 Fast, aggressive growth that robs soil,
water and nutrients from desirable plants
nearby.
 Quick adaptation to the existing
environment.
 Ability to thrive in disturbed areas (wet or
dry) and poor soil.
 Resistance to heat and drought.
 Deep, strong roots making them difficult to
eradicate.
 Lack of natural pest or predator. Invasive
species seldom show signs of disease or
pest damage.
Coast Acacia – Acacia cyclops
 Some invasive species are able to produce
toxins that inhibit competitor's growth.

© Project SOUND

What you can do about invasive weedy
plants in S. CA

1. Know what species
are a problem in
your area
2. Get rid of these
plants in your yard
3. ‘Don’t Plant a Pest’
4. Report infestations
5. Lobby to get weedy
pest plants out of
the horticultural
trade

http://resistancestudies.org/?cat=3
© Project SOUND

Don’t Plant a Pest  Iceplant/hottentot fig (Carpobrotus edulis)
 Ivy (Hedera spp.)
 Periwinkle (Vinca major)
 Pampas grass (Cortaderia selloana)
 Fountain grass (Pennisetum setaceum)
 Scotch, French, Portugese, bridal, and
Spanish brooms
 Acacia/western coastal wattle (Acacia
cyclops)
Acacia
 Myoporum (Myoporum laetum)
 Mexican fan palm (Washingtonia robusta)
 Canary island date palm (Phoenix
canariensis)
 Brazilian pepper tree (Schinus
terebinthifolius)
 Blue-gum and red-gum eucalyptus
(Eucalyptus globulus, E. camuldulensis)
 Tree of Heaven - Ailanthus altissima
http://www.cal-ipc.org/landscaping/dpp/socal.php © Project SOUND
Myoporum

I thought that was a native plant…
 Some native plants can ‘take
over’ and become weedy or
invasive:
 ‘groundcover’ natives that
spread via rhizomes
[Woodmints] or stolons
[native strawberries]
 Clonal species [Narrow-leaf
Willow; some of the shrubby
native mallows]
 Plants that grow very fast
[Calystegia]
 Plants that reseed very well in
your yard [grasses; some
wildflowers]
 Know the characteristics;
plant where you take
advantage of these
characteristics – e.g., where
you want them to take over
© Project SOUND

Climate change & invasive plants
 Gardeners may also have to cope with a new cast of characters.
Some researchers are trying to identify exotic species with weed
potential before they jump the garden fence - plants with
windblown or bird-dispersed seeds, species that reproduce
vegetatively through runners, generalists that thrive in a variety of
habitats - and working with growers and nursery folk to make sure
new invasives don't get into the horticultural trade.
 Climate change is a moving target, and some effects could turn out
to be stronger than the models account for. There's also no
foolproof way to identify which plants will become invasives. But
with weeds moving both in from wildlands and out into them, it's
safe to say that weed control will still be on every thoughtful
gardener's agenda.


© Project SOUND

Weeds 2009

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Weeds 2009