Turfgrass Herbicide Use Characteristics

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Turfgrass Herbicide Use Characteristics

• Tim R. Murphy
• The University of Georgia

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Preemergence herbicides are the foundation of
annual grass control.
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Weed seeds germinate and are controlled as they
come in contact with the herbicide.
Herbicide layer
Turfgrass roots below the herbicide layer
Preemergence herbicides do not prevent weed seeds
from germinating.
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Preemergence Options
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The majority of herbicides used for preemergence
annual grass control are dinitroanilines and
dithiopyr

• DNAs
• Barricade
• Pendulum
• Surflan
• Balan
• Treflan
• Dimension

• Best used on established turf.
• Mitotic inhibitors.
• Immobile in the soil

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Ronstar (oxadiazon)

• Not a mitotic inhibitor
• Preferred herbicide for sprigging or high traffic
  areas (athletic fields, tees, etc.)
• Preferred herbicide for preemergence goosegrass
  control
• Will control crabgrass but is more effective on
  goosegrass

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What is the best preemergence herbicide for
turfgrasses??
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It depends.
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Preemergence Herbicide Selection

• Turfgrass species
• Weed species
• Immature vs. established
• Time of year
• Irrigation capabilities
• Renovation plans

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Preemergence Herbicide Selection

• Granular or spray equipment
• Desired control level
• Application frequency
• Ornamental tolerance
• Cost??

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Annual Grass Control Ratings
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Crabgrass spp.

• Summer annual
• At least 5 species in GA (tropical, smooth,
  large, southern, blanket)
• Germinates at soil temps. - 53 to 58 F., 4 inch
  depth
• Light required

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Southern crabgrass
Smooth crabgrass
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Goosegrass

• Summer annual
• Germinates - soil temp. 4 inch depth averages 60
  to 65 F.
• Usually germinates 2 to 6 weeks later than
  crabgrass
• Light required

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goosegrass

• Summer annual
• Prefers compacted areas that are overwatered

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crowfootgrass
goosegrass
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Goosegrass Cultural Controls

• Aerify to alleviate compaction
• Redirect traffic
• Control watering
• Encourage dense turf

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Core Aerification

• Previously thought to break up herbicide layer
  and reduce weed control
• Research shows little increased crabgrass or
  goosegrass due to core aerification

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Annual bluegrass

• Winter annual
• Germinates late summer-fall at soil temperatures
  around 70 F.
• Second germination flush in mid- to late-winter

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Continuous annual bluegrass seed germination
occurred from mid-Nov. through early January in
Knoxville, TN. Callahan and McDonald, 1992
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Annual bluegrass control
Boat shaped leaf tip

• Preemergence Control
• Barricade, Pendulum
• Surflan, Dimension
• Balan, Ronstar
• Kerb
• Atrazine, Simazine

annual bluegrass
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Preemergence Herbicides

• Need rainfall or irrigation (1/2 inch)
• Do not control emerged weeds

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Preemergence Herbicides

• If irrigation is not available, apply well in
  advance of expected weed germination to allow for
  an activating rainfall.
• Loss of activity may occur if they are not
  watered in within 7 to 10 days.
• Losses from photodecomposition and volatilization
• Treflan (Team) is the most volatile, Barricade
  the least volatile.

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Relative Solubility of Preemergence Herbicides
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Preemergence Herbicide Volatility
Herbicide Vapor Pressure (mm Hg) Relative Volatility
Benefin 1.0X 10-5 Moderate
Pendimethalin 9.4 X 10-6 Low
Surflan 2.5 X 10-8 Very Low
Barricade 3.3 X 10-9 Very Low
Dimension 4.0 X 10-6 Low
Kerb 8.5 X 10-5 Moderate
Bensulide 8.0 X 10-7 Very Low
Ronstar 7.8 X 10-7 Very Low
Aatrex 2.9 X 10-7 Very Low
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Irrigation Timing and Formulation Effect on
Crabgrass Control with Pendimethalin
0 watered in immediately 7 watered in 7 days
after application
GR granular, WP Sprayable
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Granular Formulations

• Poor Distribution of Active Ingredients
• Spreader not calibrated, changes with age
• Bag settings are only guidelines
• Spreader and/or product cause a skewing of
  product distribution over the turf
• Particle size too large for uniform coverage
• Lower application rates reduce uniform coverage

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Fertilizer/Preemergence Products

• Correct fertilizer analysis??
• Time of year??
• N-release characteristics??
• Supplemental fertilizer applications??
• Supplemental herbicide applications??

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Fertilizer/Preemergence Products - Other
Considerations

• Uniform coverage required
• Uniform particle size is important
• Release characteristics of fertilizer product
• Control equivalent to sprayable and granular
  products

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Preemergence Herbicides - Formulation Effects
Yelverton, et al., 1996
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Preemergence Herbicides- Formulation Effects
Johnson and Murphy, 1991
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Preemergence Herbicides- Formulation Effects
Johnson and Murphy, 1991
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Preemergence Herbicide Timing

• Soil temperatures can vary in a neighborhood -
  south facing slopes warm earlier in the Spring
• Coarse textured soils warm more quickly than
  fine-textured soils
• Most preemergence herbicides are degraded by soil
  microorganisms - activity is less at 45 degree
  vs. 70 degree soil temp. Most warm-season grassy
  weeds germinate at 55 to 65 F. APPLY EARLY
• Can the site be irrigated for activation?

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Suggested Application Dates

• North Georgia
• Spring, March 1 - 20
• Fall, August 20 - Sept. 15
• South Georgia
• Spring, Feb. 10 - March 1
• Fall, Sept. 20 - Oct. 15
• Early is always better than late!

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Timing Summer Annual Grass Control

• Late February to early March for crabgrass
  control
• Goosegrass two to four weeks later
• Early application (late January, February) is OK
  due to slower herbicide decomposition during cool
  weather.

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Repeat Applications - Summer

• Space 8 to 10 wks apart
• Apply 1/2 X fb 1/2X
• May improve control of crabgrass and goosegrass

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Guidelines - Preemergence

• Labeled products only
• Established turfgrass
• Apply before weed emergence
• Need rainfall or irrigation within 5 days
• Consider split applications
• Delay mowing until after incorporation
• Know future plans

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Lack of Preemergence Herbicide Performance

• Applied after weed emergence
• No rainfall or irrigation
• Excessive rain after application, high rainfall
  year
• High rainfall year
• Poor site drainage
• Drought
• Rate too low
• Mow/Bag before incorporation

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Broadleaf Control

• Most broadleaf control is done with postemergence
  herbicides.
• The essential broadleaf herbicides are
• Postemergence - growth regulators and
  sulfonylureas
• Pre and post atrazine, simazine, metribuzin.
• Pre only - Gallery

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Growth Regulator Herbicides
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Broadleaf Herbicides

• There are many growth regulator combinations on
  the market.
• Mixtures of broadleaf-active herbicides tend to
  control more weed species than each individual
  component herbicide.

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Phenoxy Dicamba Herbicides
Herbicide 2,4-D MCPP MCPA 2,4-DP dicamba
Weedar 64 X
MCPP-4 X
2 Plus 2 X X
Four Power X X
Turf D DP X X
Trimec Classic X (gt) X (lt) X
Trimec Southern X (lt) X (gt) X
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Phenoxy Dicamba Herbicides
Herbicide 2,4-D MCPP MCPA 2,4-DP dicamba
Triamine X X X
Triamine II X (gt) X (lt) X
Tri-Power X (lt) X (gt) X
Dissolve X X X
Triplet X (gt) X (lt) X (gt)
Triplet Sens. X (lt) X (gt) X (lt)
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Phenoxy, Dicamba, Picolinic Herbicides
Herbicide 2,4-D MCPA clopyralid triclopyr dicamba
Lontrel X
Turflon Ester X
Confront X X
Chaser (ester) X X
Chaser II Am. X X
Cool Power (ester) X (lt) X (lt) X (lt)
HorsePower X (gt) X (gt) X (gt)
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Post Herbicide Use Guidelines

• Try to avoid spraying warm-season grasses during
  transition.
• Shade grasses are less herbicide tolerant than
  grasses growing in full sun.
• Spray when wind speeds are less than 5 mph.

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Post Herbicide Use Guidelines

• Avoid stress conditions (gt 90 F.)
• Avoid spring transition on warm-seasons
• Repeat applications
• Do not mow 24 to 48 hours before or after
  application
• Rainfall and irrigation effects

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Post Herbicide Use Guidelines

• Do not water for 12-24 hours.
• Need a rain free period of at least 6 hours.
• Avoid extreme temperatures. Apply when
  temperatures are between 40 and 80F.

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Examples of Rain-Free Periods

• MSMA - 24 hours
• Trimec Classic - 24 hours
• Basagran T/O - 8 hours
• Finale - 4 hours
• Vantage - 1 hour

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Post Herbicide Use Guidelines

• Annual weed control is excellent in the seedling
  stage and poor as the weed matures
• Perennial weeds are more susceptible in the
  Spring or Fall because root reserves are usually
  depleted and the weed has less recovery potential
• Apply to actively growing weeds - the cuticle is
  more easily penetrated
• Sprays give better control than granules.

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Post Herbicide Use Guidelines

• Repeat applications are most effective for tough
  perennials.
• Apply during good growing conditions when
  adequate soil moisture is present.
• Add a surfactant if called for on label.

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Non-Target Plants

• Check for restrictions on the use of herbicides
  around trees and shrubs.
• Be very careful around vegetables and ornamentals
  with growth regulator herbicides.
• Avoid applying dicamba and atrazine under shallow
  rooted ornamentals such as azalea and
  rhododendron.

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Nonselective Broadleaf Control

• Roundup Pro - slow acting (7-14 days) but
  provides the best control of perennials.
• Reward - fastest burndown, poor perennial
  control, poor grass control.
• Finale - Almost as fast as Reward, will leave a
  straight edge, very good on white clover and
  other legumes. Not good on perennials.

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Lack of Post Herbicide Performance

• Environmental stresses
• Weed growth stage
• Rain/irrigation wash-off
• No adjuvant
• Poor spray coverage

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Lack of Post Herbicide Performance

• Wrong rate
• Wrong herbicide
• No follow-up application
• Mowing effects