Weed identification and management

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Weed identification and management

• Jed Colquhoun
• UW Horticulture, weed ecology and management

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Weed identification and management

• What makes a plant a weed?
• Who cares? Impacts of weed invasions
• Why do weeds always win? Biology of weeds
• Get to know the enemy weed ID
• Anatomy of a weed
• Common Wisconsin weeds
• Strategies for weed management
• General techniques from vinegar to torches
• Strategies for herbicide use

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What makes a plant a weed?
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Definition of a weed

• A weed is an undesired plant out of place
• Butterfly bush in the landscape bed desirable
  ornamental
• Butterfly bush clogging a wetland marsh weed

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Weed impacts

• Weeds are costly
• 24 billion in agricultural crop loss
• 3 billion in control cost

Pimentel et al. 1999
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Weeds are costly

• Jointed goatgrass in wheat
• Infested 5 million acres wheat, 2.5 million acres
  fallow
• Spreads at a rate of 50,000 acres per year
• Reduces wheat yield by up to 50
• Cost in wheat 45 million/year

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Weeds are costly

• Kudzu in forestry
• In summer, grows about 1 foot per day
• Tap roots weigh 400 pounds
• Known as vine that ate the south
• Dominates 7 million acres in southeastern U.S.
• Host for soybean rust

Photos courtesy TNC
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Weeds reduce property value

• Leafy spurge
• Western U. S. land value reduced 83 by reducing
  grazing capacity
• Gorse
• West coast impenetrable thickets of gorse, with
  persistent growth after removal

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Weeds reduce recreational value and tourism

• Eurasian watermilfoil - Midwest
• Forms thick mats in water
• Reproduces from small fragments
• Limits boating, swimming, fishing
• Fouls water intakes, canals, flood control
• Decays in large masses on beaches

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Weeds threaten biodiversity

• Invasive weeds considered second greatest threat
  to endangered species
• Purple loosestrife
• Displaces native cattails, reeds, and sedges
• Reduces habitat for endangered bog turtles and
  ducks

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Weeds decrease water resources

• Saltcedar (Tamarisk)
• Grows along streambanks and marshes in Southwest
• Consumes more than 200 gallons of water per day
• Increases salinity of soil to the point where
  other plants will not grow

Courtesy TNC
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Weeds can endanger human health

• Giant hogweed
• Rapid, extensive growth
• Causes severe dermatitis and blistering in humans
• Introduced as an ornamental!

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Why do weeds always win?

• Dormancy broken when conditions favor survival
• Rapid early growth and expansion
• Early and fast root growth and penetration of a
  large area
• Efficient uptake and processing of nutrients and
  water

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Why do weeds always win?

• Ability to reproduce early in life cycle
• Prolific seed production
• Absorb resources in excess
• Tolerate low levels of resources
• Genetic and environmental adaptability
• Ability to develop resistance to control measures

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Reproduction by seed

• First infestation is dependant on seed
• Seed production varies greatly
• Canada thistle 700 seeds per plant
• Small broomrape 1,000,000 seeds plant
• Seed longevity can be up to 1,000 years!

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Vegetative reproduction

• Less longevity in soil than seeds
• Very small structures can reproduce
• Canada thistle ¼ root results in new plant
• Can be as prolific as seed production
• Yellow nutsedge 1,900 new plants and 18,000
  tubers in one year from one plant

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Crossing paths on their respective journeys of
destiny, Johnny Appleseed and Irving Ragweed nod
hello.
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Seed dispersal
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Weeds are for the birds

• Examples of weed seed in 6 random sources bought
  in retail shops
• Green foxtail Kochia
• Witchgrass Pigweed Common Lambsquarters
• Russian thistle Buffalobur Johnsongrass
• Nightshade Wild buckwheat Lanceleaf sage
• Safflower Barnyardgrass Common ragweed
• Downy brome Poygonum spp. Stinkgrass
• Velvetleaf Yellow bristlegrass Sage spp.
• Little burnet Asteraceae Pineappleweed
• Flax Wild poinsettia Bur ragweed
• Brassica spp. Panicgrass Jointed goatgrass
• Sandbur Sumpweed Puncturevine
• Sweet clover Broadleaf dock
• Common mallow

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Juniper seed deposited by birds on fence
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Get to know the enemy weed identification
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Weed identification is critical

• Patersons curse
• Misidentified in U.S. ten years ago
• Infests 80 million acres in Australia
• Control costs 50 million per year
• Very persistent
• Toxic to most animals

Australian Broadcast Co.
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Weed classification life cycles

• Annual
• Life cycle completed in one year
• Rely on seed production for species survival
• In general, easiest plant form to manage
• Examples common lambsquarter, redroot pigweed

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Weed classification life cycles

• Biennial
• Life cycle completed in two years
• Flowering and fruiting in second year
• Examples wild carrot, poison hemlock

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Perennial weed classification

• Simple perennials
• Spread by seed only, not vegetatively
• HOWEVER, vegetative structures can regenerate
  when injured or cut!
• Examples common dandelion, plantain

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Perennial weed classification

• Creeping perennials
• Reproduce vegetatively and by seed
• Most difficult to control
• Examples Canada thistle, field bindweed,
  quackgrass

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Weed identification goals

• The goal today is not to learn the thousands of
  weeds encountered in the Midwest
• The goal is to learn how to identify a weed
• Plant anatomy
• Plant keys
• Useful resources

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Anatomy of a weed grass seedlings
Source Hartmann et al. 1988. Plant Science
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Anatomy of a weed broadleaf seedlings
Source Hartmann et al. 1988. Plant Science
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Anatomy of a weed roots

• Distinguishing root characteristics
• Fibrous vs. tap root
• Lateral roots
• Root hairs

Tap root
Fibrous root
Source Hartmann et al. 1988. Plant Science
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Anatomy of a weed stems

• Shape round (velvetleaf), angular (common
  lambsquarters), flat (annual bluegrass),
  triangular (nutsedge)
• Hairy vs. smooth
• Color

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Anatomy of a weed leaves

• Arrangement opposite vs. alternate vs. whorled
• Texture hairy vs. smooth, rough vs. waxy
• Veination parallel (grasses) vs. broad
  (broadleaves)
• Leaf shape
• Grass ligules present or absent, membranous or
  hairy

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Plant keys

• Start broad, narrow choices
• Series of yes/no questions take them one at a
  time, go back one step if necessary
• Double check answer with visual image, such as
  National Plants Database (http//plants.usda.gov/)

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Weed identification resources
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Common Wisconsin weeds

• Common lambsquarters
• Annual
• Broadleaf (dicot)
• Fibrous roots
• Angular stem
• Opposite leaves with powdered sugar

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Common Wisconsin weeds

• Yellow nutsedge
• Perennial with tuberous creeping roots
• Triangular stem
• Glossy, stiff leaves with no hair

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Common Wisconsin weeds

• Canada thistle
• Creeping perennial
• Spiny margins, lobed leaves
• Seedling leaves covered with hair
• Older leaves smooth on top
• Pink to purple flowers

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Common Wisconsin weeds

• Giant foxtail
• Annual
• Grass
• Round, rolled stem
• Hairy ligule
• Long, wiry hairs on upper leaf surface
• Leaf margin also hairy
• Fox tail-like seedhead

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Common Wisconsin weeds

• Wild carrot, Queen Annes Lace
• Biennial
• Roots have carrot odor
• Very dissected, fern-like leaves with carrot odor
• Several white umbels per plant, with red dot in
  center of umbel

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Weed management strategies
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3 best methods of weed control

• Prevention
• Prevention
• Prevention

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Only you can prevent weed invasion!

• Get to know the enemy
• Communicate geographically and between groups
• Keep an eye out for new invaders elsewhere
• Consider all points of entry
• Prevent reproduction of early invaders
• Be careful what you plant tag-a-longs

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Ecological weed management is based on how a
plant is built

• Annual vs. biennial vs. perennial
• Growth stage perennials act like annuals for a
  short period
• Timing relative to the seasons

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Management timing relative to the seasons

• Perennial weed growth schedule
• Spring export carbohydrates from roots to new
  shoots
• Summer capture and assimilate new energy
• Fall pack it in for winter carbohydrates
  transported to the roots
• Winter usually, minimal growth or activity

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Management timing relative to the seasons

• Perennial weed management general terms
• Spring limit new growth drain the roots
• Summer prevent energy capture
• Fall opportunity to attack the root storage
  system
• Winter eliminate new seedlings

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Manual removal

• Success determined by population and distribution
  is it feasible?
• Annual weeds easily removed
• Perennial plants are often subdivided
• Vegetative root pieces often produce new plants

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Biological control

• Several success stories
• Tansy ragwort
• Purple loosestrife
• Grazing blackberry
• Biological control of weeds is a difficult
  proposition

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Challenges to biological control

• The control agent must be very host-specific and
  not injure non-target species
• Survival in new climates can be difficult
• The life cycle of the control agent must match
  that of the target species
• Surrounding habitat should support control agent
  survival and reproduction

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Stale seedbed a fresh start

• Till soil to final seedbed
• Allow weeds to germinate (irrigate if necessary)
• Remove/control germinated weeds
• Manual removal
• In dry months, shut off water
• Herbicides
• Plant desirable species (minimal tillage)

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Solarization

• Clear polyethylene mulch traps solar energy
• Intense heat and sunlight required, often for
  about a month
• Weed seed cell structure is damaged and microbial
  degradation is high
• After solarization, mulch is removed

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Solarization

• Emergence of annual grass and broadleaf weeds can
  be reduced up to 99
• Effective only in upper soil layers
• Small-seeded weeds controlled better than
  large-seeded weeds
• Perennial weeds not controlled as well
• Moist soil traps heat better than dry soil

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Flame weeding

• Propane fueled burners for weed control
• Idea is not to burn off weeds, just break cell
  membranes (dark green color after flaming)
• Controls primarily young, emerged annual
  broadleaf weeds that have exposed growing points

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Flame weeding

• Grass and perennial weed control often poor, with
  re-growth after treatment
• Grass weeds growing point often below-ground
• Perennial weeds re-grow from root tissue
• Energy costs are high

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Corn gluten meal

• Corn gluten meal is a protein by-product of wet
  milling for animal feed
• Inhibits root growth at seed germination, leading
  to plant moisture stress
• Applied prior to weed emergence
• Contains 10 nitrogen
• Applied after weed emergence, likely fertilizing
  weeds

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Corn gluten meal

• Non-selective will prevent weed and DESIRABLE
  plant emergence
• Results have been very mixed
• Species dependent
• Perennial, established weeds not controlled

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Vinegar/acetic acid

• Burns back emerged weeds
• Can be dangerous to humans (check labeling
  requirements cant just pour out the vinegar as
  a herbicide)!
• Very mixed results
• Perennial and established annual weeds often
  re-grow
• Non-selective will also injure desirable plants

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Herbicides

• Active ingredient vs. trade name
• Similar to the ingredient list in food items

www.naturallandscapes.org
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Selectivity application and placement

• Pre vs. post herbicides
• Contact vs. translocated herbicides
• Soil placement

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Selectivity herbicide uptake
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Herbicide translocation
Water
Sugar
Nutrients
Amino acid
Xylem
Phloem
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Selectivity metabolism

• Herbicide activation vs. deactivation
• Speed of metabolism is important

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Selectivity target site

• Absent in tolerant plants
• Altered in some herbicide resistant plants

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Common herbicides

• Growth regulators
• 2,4-D (turf mixes)
• MCPP (turf mixes)
• dicamba (turf mixes)
• triclopyr (brush control)
• glyphosate (Roundup, etc.)
• Read label prior to ANY herbicide use!!!!

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Growth regulatorsweeds controlled

• 2,4-D, dicamba, MCPP broadleaf, annual weeds
• Triclopyr broadleaf perennial weed control
• Postemergence, seedlings, shorter soil residual

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Growth regulatorsplant systems involved

• Plant hormones chemical signals that coordinate
  plant activities
• germination
• growth
• reproduction
• death

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Growth regulatorsmode of action
upset hormone balance disrupt cell enlargement
and cell division uneven or abnormal plant
growth plant death
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Growth regulators selectivity

• Grasses absorb and transport growth regulators
  less effectively than broadleaves, and metabolize
  them faster
• Grasses can still be injured or killed!
• Within broadleaves, controlled species metabolize
  growth regulators slowly

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Growth regulatorssymptoms
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Growth regulatorssymptoms
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Growth regulatorssymptoms
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Growth regulatorsstrengths

• Economical
• Minimal resistance development
• Old standby, the kinks are worked out
• Broad spectrum broadleaf control

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Growth regulatorsweaknesses

• Established and perennial weeds can be difficult
  to control
• Drift and volatilization risks
• Persistence in compost

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Herbicide persistence in compost
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Glyphosateplant systems involved
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Glyphosatemode of action
herbicide binds to enzyme amino acid production
halted 70 of carbon in plant is missing
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Glyphosatesymptoms
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Glyphosatesymptoms
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Glyphosatesymptoms
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Glyphosatestrengths

• Perennial weed control
• Non-selective, broad spectrum
• Relatively low toxicity concerns
• Limited soil residual

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Glyphosateweaknesses

• Non-selective kills or damages almost
  everything!
• No residual weed control
• Poor control in drought conditions
• Resistance development old tools dont work
  anymore

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Susceptible 1 pint/Acre (21 DAT)
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Resistant 1 pint/Acre
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Resistant 4 pints/Acre
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Resistant 8 pints/Acre
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