Weed Science Principles for Master Gardeners

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Weed Science Principlesfor Master Gardeners

• Russell W. Wallace, Ph.D.
• Extension Vegetable Weed Specialist

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Definitions of a Weed

• Any plant that is growing out of place.
• A plant that has no known benefit to man.
• A plant that has not learned to grow in rows.
• The Creators torture of man.

Proboscidea louisianica (Nutt.) S. Wats. a.k.a.
Devils-Claw
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Why Control Weeds?

• Weeds are competition for
• Nutrients
• Moisture
• Light
• Space
• Destroy equipment
• Reduce quality of produce
• Reduce profits to grower/gardener

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Weed Biology
Grasses Broadleaves Sedges Annuals Perennials
Weed Science Society of America
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Weed Science Society of America
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Weed Science Society of America
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Methods of Weed Control

• Chemical
• Cultural
• Mechanical (physical)
• Biological
• Preventative

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Chemicals

• Use of manufactured herbicides to control
  perennial and annual weed species.

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Chemicals

• Flame weeders

Colorado State University
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Timings of Chemical Sprays

• Preplant incorporated (PPI)
• Applied before planting, mixed into the soil.
• Preemergence (PRE)
• Applied to soil before planting/weed emergence
• Postemergence (POST)
• Applied after crop emerges.
• Post-Directed (P-DIRECT)
• Applied after crop emergence, directed around
  crops.
• Lay-by
• Sprayed to soil around crop before or after
  emergence.

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Classifications of Herbicides
Grass killers Broadleaf killers Contact System
ic Selective Non-Selective
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Principles of Herbicide Selectivity
Herbicide placement Anatomical
differences Foliar retention Protected
growing points Differential susceptibility at
various plant growth stages Dormancy of crop
at time of application
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Principles of Herbicide Selectivity
Use of antidotes (safeners) Examples (Eptam,
Dual Magnum) Localized application of
absorbents (activated charcoal) Internal
factors Differential translocation to site of
action Absorption or accumulation at inactive
sites Differential metabolism by
crop Differential quantity/kind of seed
reserves Resistance at site of action
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Examples of Herbicide Selectivity
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What Happens to Herbicides After They Are Sprayed?
Volatilize and dissipate through air. Remain
on leaf surface as liquid or crystal. Penetrate
leaf cuticle (waxy layer) and stay
there. Penetrate leaf cuticle, enter cell wall
and move apoplastically through xylem
system Penetrate leaf cuticle, enter cell wall
and move symplastically (through phloem system).
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Areas of Herbicide Absorption
Foliage (leaves) POSTEMERGENCE Seedling
shoots Roots (root hairs) PREEMERGENCE
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Spray Additives Surfactants, Wetting Agents,
Stickers, Spreaders
Uniform spreading of spray solutions. Help
spray to remain on leaf surface. Assure that
droplets do not remain suspended on leaf
hairs. Partially solubilize the plant surface to
allow better penetration.
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Classifications of Herbicides
Wettable Powders (WP) Emulsifiable Concentrates
(EC) Water Dispersable Granules (WDG) Granules
(G) Soluble Powders (SP) Liquids
(L) Microencapsulated (M) Aqueous Suspension
(AS)
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Herbicide Active Ingredients
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Cultural

• Smother crops
• (living)
• Crop rotation
• Hand pulling
• Hoeing
• Mowing
• Water management
• Mulching
• (dead)

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Cultural

• Smother crops
• (living)
• Crop rotation
• Hand pulling
• Hoeing
• Mowing
• Water management
• Mulching
• (dead)

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Mechanical (physical)

• Cultivation
• Plastic films
• Weed fabrics

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Mechanical (physical)
Spider gangs Tine weeders Brush hoe
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Biological

• Utilizing natural enemies for control of weeds

1. Insects 2. Diseases 3. Mammals 4. Fish 5.
Birds 6. Natural compounds found in
organisms
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Biological
Biological weed control uses host specific
diseases and insects to integrate with and to
reduce herbicide use.
Rust fungus on quackgrass
Puncture vine weevils in Pacific Northwest
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Preventative

• Obey local, state, federal and international laws
  regulated seed transportation.
• Use certified weed-free crop seed.
• Use weed-free manure and hay.
• Clean cultivation and harvesting equipment
  between fields.
• Eliminate weed infestations near or around
  irrigation ditches or cultivated fields.
• Practice zero tolerance.

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Integrated Weed Management The use of two or
more of the recognized weed control categories.
Mechanical (physical)
Chemical
Preventative
Cultural
Biological
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Organic Mulches

• Bark (grounded and chipped)
• Attractive, physical suppression, watch for
  floating during heavy rains.
• Wood chips
• Physical suppression, watch for floating during
  heavy rains.
• Grass clippings
• Physical suppression, watch out for any
  herbicides that were applied to the lawn.
  Good source of added nitrogen.

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Organic Mulches

• Newspapers (shredded)
• Readily available, inexpensive, suppress weeds.
  Susceptible to high winds, watch out for earwigs,
  and ink could possibly be toxic.
• Pine needles
• Harder to get hold of, decrease soil pH (more
  acid), leachates can suppress weeds, slow to
  break down.
• Sawdust
• Improves soil organic matter, inexpensive, could
  cause problems with water penetration, and may
  alter the nitrogen balance in the soil (may need
  to add more nitrogen). Watch out for toxic
  chemicals in wood.

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Herbicides (Background)

• Trade name
• Roundup
• Active ingredient
• Glyphosate
• Chemical
• N-(phosphonomethyl)glycine

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Herbicides (Background)

• Granules
• Difficult to apply evenly
• Concentrates -
• Powders
• Granulars
• Liquids
• Tablets
• Ready-To-Use
• Generally 98 water
• Extremely costly on a.i. basis

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Herbicides (Background)

• Types of herbicide applications
• Preemergence applied before/after seeding or
  transplanting vegetables and ornamentals,
  incorporated or just surface-applied.
• Postemergence applied over the top of seedlings
  or mature plants (either dormant or actively
  growing), vegetables or ornamentals.

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Herbicides (Background)

• Herbicide types
• Contact when applied over the top of plants it
  does not translocate but causes death only to the
  plant parts/cells it contacts.
• Systemic when applied over the top of plants
  and it translocates (moves) throughout and kills
  the entire plant, including underground
  reproductive organs.

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Home Owner Use

• Always follow the label instructions!
• Watch out for drift or volatilization to
  non-target plants and areas, residual carryover,
  plant injury, and plant death, etc. Phenoxy type
  herbicides like 2,4-D, etc., can injure irises.

Some plants are extremely sensitive!
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Home Owner Use
2,4-D (phenoxy) injury on roses not sure if it
will make it back
(April 24, 2006)
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Home Owner Use
2,4-D (phenoxy) injury on shrubs
(April 24, 2006)
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Herbicide Labels

• Always read and follow label instructions.
• Be sure to know application timing and methods,
  label restrictions, areas of use, weeds
  controlled, crop/plant use, and human safety
  information.
• Precautionary Statements (on all labels)
• Harmful if swallowed. Do not breathe spray mist.
  Avoid contact with skin, eyes and clothing.
  Users should wear long sleeve shirts and long
  pants or equivalent, chemical resistant gloves
  and boots. Wash thoroughly after handling and
  before eating and smoking. Avoid contamination
  of feed and food-stuffs. Keep children and pets
  off the treated area until the spray has dried.
  Food utensils such as teaspoons and measuring
  cups should not be used for food purposes after
  use with this product.

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Useful References

• Cornell University
• Weed Control for the Home
  Vegetable Garden (1989)
• Website http//www.gardening.cornell.edu/
• University of California-Davis
• Weed Management in Lawns (2004)
• Weed Management in Landscapes (2001)
• Website http//www.ipm.ucdavis.edu/

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Weed Control in Landscape Beds
Not all ornamentals are listed on chemical
labels. Spray on a few plants before using on a
large area.
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Weed Control in Home Gardens
Some areas are just too small to use chemicals!
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Weed Control in Lawns
http//aggie-turf.tamu.edu
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Spraying Herbicides
Remember Herbicides are intended to kill plants!
The hazards of spraying!
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Retail Distributors of Herbicides

• Bayer
• Dragon
• fertilome
• Green Light
• Hi-Yield
• Monsanto
• Monterey
• Ortho
• Preen
• Scotts
• Southern Ag

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Distributor Websites (may be others)

• Ambrands www.amdro.com
• Bayer www.bayeradvanced.com
• Dragon www.dragonchemical.com
• fertilome www.fertilome.com
• Green Light www.greenlightco.com
• Hi-Yield www.fertilome.com (branded
  products)
• Monsanto www.roundup.com
• Monterey www.montereylawngarden.com
• Ortho www.ortho.com
• Preen www.preen.com
• Scotts www.scotts.com
• Southern Ag www.southernag.com

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Herbicide Retail Products

• Method of application
• Use in West Texas
• Retail names
• Weeds controlled
• Mechanism of action
• Soil residual
• Unique characteristics (if any)
• Available organic products

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Eptam

• Preemergence control
• In flowers and ornamentals, Irish potatoes and
  green beans (home garden).
• Active ingredient
• EPTC (Hi-Yield)
• Controls 13 grasses, 13 broadleaves, 2
  sedges.

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Eptam

• Symptomology
• Weeds fail to emerge, or injured plants appear
  with malformed leaves and twisted seedlings.
  Grass leaves rolled tightly and do not unroll.
  Broadleaves may have cupped or crinkled leaves.
• Soil residual
• Very short, 2 3 weeks, less active in soils
  with high organic matter. Very
  volatile in soil, needs to be
  incorporated by mixing soil or with water.

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Glyphosate

• Postemergence control
• (a.k.a. Roundup)
• Use in West Texas
• Walkways, driveways, patios, flower beds, around
  fence lines, buildings, trees and shrubs.
  Non-selective herbicide.
• Other retail names
• KillZall (Hi-Yield)
• Weed Grass Killer (Preen)
• Power Force Grass Weed Killer (Bayer)
• Remuda Full Strength (Monterey)
• Nutgrass, Poison Ivy Vine Killer (fertilome)
• Controls Annual and perennial grasses
  broadleaves, as well as
  unwanted shrubs and vines.

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Glyphosate

• Symptomology
• Growth is inhibited followed by leaf yellowing
  and death within 4 7 days (susceptible weeds)
  and 10 20 days for less susceptible plants.
  Leaf yellowing more pronounced in immature leaves
  and growing points.
• Soil residual
• None.

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Herbicidal Soap

• Postemergence control
• Contact action within hours, avoid contact with
  any desirable plants. Will not
  control underground reproductive tissues.
• Use pattern
• Preplant applications
• Active ingredient
• Ammoniated salt of fatty acids
  (Monterey)
• Controls Small grasses and broadleaves

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Herbicidal Soap

• Soil residual
• None
• Unique characteristics
• Some products are organically certified, but can
  still cause skin irritation and eye injury.

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Image

• Pre and Postemergence control
• Good for nutsedge control
• Use in West Texas
• In turf (bermudagrass, zoysiagrass) and selected
  landscape ornamentals.
• Active ingredient
• Imazaquin (AMBRANDS)
• Controls 8 grasses, 22 broadleaves, 6 sedges.

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Image

• Symptomology
• Growth inhibition with 1 to 2 weeks, yellow
  meristems followed by general foliar yellowing
  and death.
• Soil residual
• May last up to 1 year depending on crop to be
  planted.

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Manage

• Pre and postemergence control
• Small broadleaves and nutsedge
• Use in West Texas
• Established lawns, ornamental turf, and
  landscaped areas.
• Active ingredient
• Halosulfuron (Monsanto)
• Controls Nutsedge and some broadleaves

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Manage

• Symptomology
• Rapid growth inhibition with POST applications,
  leaf yellowing occurs within 3 7 days, and
  death of plant in 7 14 days. PRE applications
  cause shoots to become yellow and die soon after
  weed emergence. Slow death to weeds.
• Soil residual
• Low mobility, with short to moderate persistence.

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Nutgrass Nihilator

• Postemergence control
• For annual broadleaf weeds and nutsedge.
• Use in West Texas
• Established turf, ornamentals and groundcovers.
• Active ingredient
• Bentazon (Monterey)
• Controls 19 small broadleaves and nutsedge.

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Nutgrass Nihilator

• Symptomology
• Leaf yellowing begins in 3 5 days followed by
  foliar desiccation and death. Bronzing may occur
  on tolerant crops.
• Soil residual
• None

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Over-The-Top Grass Killer

• Postemergence grass control
• Annual and perennial grasses
• Use in West Texas
• Annual and perennial flower and shrub beds,
  groundcovers, herbaceous plants and evergreens.
  Safe on fountain and mondo grasses.
• Active ingredient
• Fluazifop-p-butyl (fertilome)
• Controls 19 annual and 16 perennial grasses

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Over-The-Top Grass Killer

• Symptomology
• Translocates slowly throughout the entire plant
  in the phloem. Growth ceases soon after
  application, leaf chlorosis developing on young
  and actively growing tissues first. Older leaves
  turn purple, orange or red before becoming
  necrotic.
• Soil residual
• None.

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Power Force Grass Weed Killer

• Postemergence control
• General weed control
• Use in West Texas
• Walkways, driveways, patios, flower beds, around
  fence lines, buildings, trees and shrubs.
  Non-selective activity.
• Active ingredient
• Glufosinate-ammonium (Bayer)
• Controls grasses, broadleaves, unwanted brush
  and vines.

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Power Force Grass Weed Killer

• Symptomology
• Leaves turn yellow and wilt within 3 5 days
  followed by death in 1 2 weeks.
• Soil residual
• No soil activity.

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Trifluralin

• Preemergence control
• (a.k.a. Treflan, etc.)
• Use in West Texas
• Ornamental and vegetable gardens, and established
  bermudagrass, ryegrass, zoysiagrass, and fescues.
• Retail Names
• Vegetable and Ornamental Weeder (Monterey)
• Garden Weed Preventer (Preen)
• Crabgrass Control (Hi-Yield)
• Controls Over 15 annual grasses, and 12
  broadleaves.

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Trifluralin

• Symptomology
• Weeds fail to emerge due to inhibition of
  coleoptile or hypocotyl growth, as well as
  inhibition of root growth. Roots appear stubby
  and tips become thickened.
• Soil residual
• 2 6 months.
• Unique characteristics Needs incorporation,
  tightly adsorbed to organic matter in the soil.

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Vantage, Grass Getter, Grass Killer

• Postemergence grass control
• Use in West Texas
• Ornamental landscape beds, around trees, patios,
  driveways, groundcovers, shrubs, wildflowers,
  non-bearing food crops.
• Active ingredient
• Sethoxydim (Monterey, Hi-Yield, Southern Ag)
• Controls 35 annual and perennial grasses.

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Vantage, Grass Getter, Grass Killer

• Symptomology
• Translocates slowly throughout the entire plant
  in the phloem. Growth ceases soon after
  application, leaf yellowing develops on young and
  actively growing tissues first. Older leaves
  turn purple, orange or red before dying. Takes 1
  3 weeks.
• Soil residual
• None.

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Weed Impede

• Preemergence control
• Older chemistry
• Uses in West Texas
• Landscaper ornamentals, bedding plants,
  non-bearing fruit and nut trees, established warm
  season turf, ornamental bulbs, ground covers,
  non-bearing vineyards, non-planted areas.
• Active ingredient
• Oryzalin (Monterey)
• Controls 26 grasses, 19 broadleaves and
  suppresses many others.

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Weed Impede

• Symptomology
• Weeds fail to emerge due to inhibition of
  coleoptile or hypocotyl growth, as well as
  inhibition of root growth. Roots appear stubby
  and tips become thickened.
• Soil residual
• 2 6 months.

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Natural Herbicides

• Granules
• Concentrates -
• Granular
• Liquid
• Ready-To-Use

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Corn gluten meal

• Preemergence control
• Granular, use around established vegetables
• Use in West Texas
• Vegetable gardens and lawns
• Retail name
• Vegetable Garden Weed Preventer (Preen)
• Corn Weed Blocker (Down to Earth)
• Controls
• 9 grasses, 10 broadleaves (including crabgrass,
  dandelion, pigweed and lambsquarters).

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Corn gluten meal

• Mechanism of action
• Prevents the normal development of roots from
  sprouting seeds. Does not kill directly but
  causes seedlings with less than normal root
  systems to succumb to dehydration when exposed to
  drought stress.
• Symptomology
• Deformed emerging weeds.
• Soil residual
• Use 10 20 lbs/ 1000 sq. ft, up to 4 6 weeks
  residual.
• Unique characteristics Biological by-product,
  must be watered in, no control for
  established weeds.

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Essential plant oils

• Active ingredients
• Clove, thyme, and/or
  cinnamon oils
• Use in West Texas
• Postemergence burn down
• Retail names
• Xpress, Matran II, Weed Zap, Natures Glory Weed
  and Grass Killer
• Controls Broad spectrum

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Essential plant oils

• Mechanism of action
• Contact herbicides. Will not kill unexposed
  growing points.
• Symptomology
• Rapid desiccation of the leaves
  and stems.
• Soil residual
• None.
• Unique characteristics Smell better than
  standard herbicides!

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Pelargonic Acid

• Postemergence control
• Use in West Texas
• Contact, non-selective control of grasses and
  broadleaf weeds prior to planting.
• Retail name
• Scythe (Mycogen)
• Controls grasses, broadleaves

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Pelargonic Acid

• Mechanism of action (Fatty acid)
• Disrupts membrane permeability resulting in cell
  leakage and death.
• Symptomology
• Rapid cell and leaf death (within hours).
  Foliage turns dark and water-soaked.
• Soil residual
• None.

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Vinegar (acetic acid)

• Postemergence control
• (a.k.a. Concentrated vinegar 25).
  Cooking vinegar is 5 acetic
  acid.
• Use in West Texas
• Preplant burn down, or directed spray.
• Retail name
• Burnout II Weed Grass Killer (St. Gabriels
  Laboratories), also contains lemon juice and
  clove oil.
• Natures Glory Weed Grass Killer (Monterey)
• Controls Multiple annual grasses and
  broadleaves, will not kill the growing points of
  plant unless contacted.

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Vinegar (acetic acid)

• Mechanism of action
• Contact, no translocation, cellular disruption.
• Symptomology
• Leaves turn black and water-soaked within hours.
• Soil residual
• None.
• Unique characteristics Costs up to 65/A.

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Any Questions?
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Thats it for your basic review of Weed Science
Principles!

• Any Questions?
• Contact information
• rwwallace_at_ag.tamu.edu
• http//lubbock.tamu.edu/horticulture/