Maximizing Preemergence Herbicide Performance in Tall Fescue

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Maximizing Preemergence Herbicide Performance in
Tall Fescue

• Tim R. Murphy
• The University of Georgia

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Tall Fescue/Southern Transition Zone

• Growth slows in high heat and humidity
• Susceptible to brown patch (only limited
  resistance in commercial varieties)
• Turf density decreases with resultant decrease in
  competitive ability
• Often reseeded annually or every other year

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Differential large crabgrass control in tall
fescue. Johnson, 1993
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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 for Tall Fescue
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Annual Grass Control Ratings
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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.
• Trifluralin is the most volatile, Surflan the
  least volatile.
• Losses from photodecomposition and volatilization

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Irrigation Timing and Formulation Effect on
Crabgrass Control with Pendimethalin
WP Sprayable, 7 watered in 7 days after
application
GR granular, 0 watered in immediately
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Maintain Healthy Turfgrass

• Manage the roots to have good shoots
• Soil testing is a must!
• Utilize cultural practices (fertility,
  irrigation, mowing height, etc.) to improve
  stress tolerance
• Keep mower blades sharp !

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Brown Patch in Tall Fescue

• Rhizoctonia solani
• Favored by night temps. gt 60 F. and gt 10 hrs.,
  foliar wetness for several days
• Cloudy weather, poor soil drainage, lack of air
  movement, late afternoon watering
• Severity increases with excessive N fertilization
  and on soils low in P and K

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Smooth Crabgrass Control - Pendimethalin


Rated 8/23/99
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Smooth Crabgrass Control - Prodiamine
Rated 8/23/99
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Smooth Crabgrass Control - Oxadiazon
Rated 8/23/99
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Reseeding Restrictions
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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.
• Relatively immobile in the soil
• Spring applications can thin fall-seeded fescue

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Tolerance of Fall-Seeded Tall Fescue to
Spring-Applied Preemergence Herbicides

• B. J. Johnson T. R. Murphy
• The University of Georgia

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Methods

• Seeded Ky 31 in mid-Sept., -Oct. and
• -Nov.
• Applied herbicides on Feb. 28
• 2 yr. study
• Recorded quality and density ratings following
  spring and early summer

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Tolerance of Fall-Seeded Tall Fescue to Pre
Herbicides
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Results

• No herbicide reduced density of tall fescue
  seeded in mid-Sept. or mid-Oct.
• Pendimethalin, XL, Dimension, and Surflan reduced
  density 17 to 40 for fescue seeded in mid-Nov.
  in both yrs.
• In 1 of 2 yrs. Balan and Ronstar reduced density

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Fall-Seeded Tall Fescue

• Related study showed that early-Nov. seeded tall
  fescue was tolerant to Feb. 1 Apr. 1, Mar. 1
  May 1, or Apr. 1 June 1 applications of
  Barricade at 0.5 0.5 lbs. ai/acre
• Prinster, SWSS Proc. 47255.

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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 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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Timing Summer Annual Grass Control

• Late February to early March for crabgrass
  control
• Goosegrass two to four weeks later
• Early application (late January to early
  February) is OK due to slower herbicide
  decomposition during cool weather. (do only in
  well-established tall fescue)

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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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Avoiding Phytotoxicity

• Read the label to make sure the herbicide is
  registered for use on the turf
• Apply the herbicide at the recommended rate and
  determine application intervals
• Test unfamiliar products and tank mixes on a
  small scale

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Avoiding Phytotoxicity

• Keep sprayers calibrated and in good working
  order
• Agitate spray mixture
• Avoid application to stressed turfgrasses
• Keep accurate records of all applications