Turfgrass Herbicide Use Characteristics

Tim R. Murphy

The University of Georgia

Preemergence herbicides are the foundation of annual grass control.

Turfgrass roots below the herbicide layer

Herbicide layer

Weed seeds germinate and are controlled as they come in contact with the herbicide.

Preemergence herbicides do not prevent weed seeds from germinating.

Preemergence Options

Atrazine Pendimethalin Simazine Kerb Balan Dimension XL Bensulide TeamPro Pennant Surflan Gallery Barricade Ronstar

The majority of herbicides used for preemergence annual grass control are dinitroanilines and dithiopyr

DNA’s Barricade Pendulum Surflan Balan TreflanDimension

Best used on established turf.

Mitotic inhibitors. Immobile in the

soil

Ronstar (oxadiazon)

Not a mitotic inhibitorPreferred herbicide for sprigging or high

traffic areas (athletic fields, tees, etc.)Preferred herbicide for preemergence

goosegrass controlWill control crabgrass but is more effective

on goosegrass

What is the best preemergenceherbicide for turfgrasses??

It depends……….

Preemergence Herbicide Selection

Turfgrass speciesWeed speciesImmature vs. establishedTime of yearIrrigation capabilitiesRenovation plans

Preemergence Herbicide Selection

Granular or spray equipmentDesired control levelApplication frequencyOrnamental toleranceCost??

Annual Grass Control Ratings

Herbicide

Crabgrass

Goosegrass

Annual Bluegrass

Benefin G F G-E Benefin + oryzalin G-E F-G G-E Benefin + trifluralin F-G F G-E Bensulide E P P-F Dithiopyr G-E F-G G-E Oryzalin G-E F-G G-E Oxadiazon G G-E G-E Pendimethalin G-E F-G G-E Prodiamine G-E F-G G-E

Crabgrass spp.

Summer annualAt least 5 species in GA (tropical, smooth,

large, southern, blanket)Germinates at soil temps. - 53 to 58 F., 4

inch depthLight required

Southern crabgrass

Smooth crabgrass

Goosegrass

Summer annualGerminates - soil temp. 4 inch depth

averages 60 to 65 F.Usually germinates 2 to 6 weeks later than

crabgrassLight required

goosegrass

Summer annual Prefers compacted areas that

are overwatered

goosegrasscrowfootgrass

Goosegrass Cultural Controls

Aerify to alleviate compaction Redirect trafficControl wateringEncourage dense turf

Core Aerification

Previously thought to break up herbicide layer and reduce weed control

Research shows little increased crabgrass or goosegrass due to core aerification

Annual bluegrass

Winter annualGerminates late summer-fall at soil

temperatures around 70 F.Second germination flush in mid- to late-

winter

Continuous annual bluegrass seedgermination occurred from mid-Nov.through early January in Knoxville, TN.

Callahan and McDonald, 1992

Annual bluegrass control

Preemergence Control Barricade, Pendulum Surflan, Dimension Balan, Ronstar Kerb Atrazine, Simazineannual bluegrass

Boat shaped leaf tip

Preemergence Herbicides

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

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.

Relative Solubility of Preemergence Herbicides

0.275 0.30.013

0.7

2.6

0

1

2

3

4

5

Surflan Ronstar Pendimet Treflan Barricade

ppm

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

Irrigation Timing and Formulation Effect on Crabgrass Control with Pendimethalin

0

5

10

15

20

25

30

35

40

45

Pla

nts/

sq.

ft.

GR 0 WP 0 GR 7 WP 7

GR = granular, WP = Sprayable

0 = watered in immediately

7 = watered in 7 days after application

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

Fertilizer/Preemergence Products

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

Fertilizer/Preemergence Products - Other Considerations

Uniform coverage requiredUniform particle size is importantRelease characteristics of fertilizer productControl equivalent to sprayable and

granular products

Preemergence Herbicides - Formulation Effects

Barricade

lbs. ai/acre

Smooth Crabgrass Control (%)

65WG 0.75 98

0.29G 0.75 91

0.5G 0.75 81

Yelverton, et al., 1996

Preemergence Herbicides- Formulation Effects

% Control

Dimension

lbs. ai/acre

Smooth Crabgrass

Goosegrass

1EC 0.5 64 31

1EC 0.75 91 29

0.25G 0.25 82 55

0.25G 0.38 100 78

0.25G 0.5 100 82 Johnson and Murphy, 1991

Preemergence Herbicides- Formulation Effects

% Control

Dimension

lbs. ai/acre

Large Crabgrass

Goosegrass

1EC 0.25 + 0.25 88 72

18-3-12G 0.25 + 0.25 96 94

Johnson and Murphy, 1991

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?

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!

Timing Summer Annual Grass Control

Late February to early March for crabgrass control

Goosegrass two to four weeks laterEarly application (late January, February) is

OK due to slower herbicide decomposition during cool weather.

Repeat Applications - Summer

Space 8 to 10 wks apartApply 1/2 X fb 1/2XMay improve control of crabgrass and

goosegrass

Guidelines - Preemergence

Labeled products onlyEstablished turfgrassApply before weed emergenceNeed rainfall or irrigation within 5 daysConsider split applicationsDelay mowing until after incorporationKnow future plans

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

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

Growth Regulator Herbicides

Phenoxy Picolinic Acid Benzoic Acid

2,4-D Lontrel Banvel

dichlorprop Turflon D Vanquish

mecoprop

MCPA

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.

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 (>) X (<) X

Trimec Southern X (<) X (>) X

Phenoxy + Dicamba Herbicides

Herbicide 2,4-D MCPP MCPA 2,4-DP dicamba

Triamine X X X

Triamine II X (>) X (<) X

Tri-Power X (<) X (>) X

Dissolve X X X

Triplet X (>) X (<) X (>)

Triplet Sens. X (<) X (>) X (<)

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 (<) X (<) X (<)

HorsePower X (>) X (>) X (>)

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.

Post Herbicide Use Guidelines

Avoid stress conditions (> 90 F.)Avoid spring transition on warm-seasonsRepeat applicationsDo not mow 24 to 48 hours before or after

applicationRainfall and irrigation effects

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 80°F.

Examples of Rain-Free Periods

MSMA - 24 hoursTrimec Classic - 24 hoursBasagran T/O - 8 hoursFinale - 4 hoursVantage - 1 hour

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.

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.

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.

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.

Lack of Post Herbicide Performance

Environmental stressesWeed growth stageRain/irrigation wash-offNo adjuvantPoor spray coverage

Lack of Post Herbicide Performance

Wrong rateWrong herbicideNo follow-up applicationMowing effects