Spring and Fall Preemergence Spring and Fall Preemergence Weed Control Options for TurfWeed Control Options for Turf

Dr. Tim R. Murphy

Extension Weed Specialist

University of Georgia

Griffin

Preemergence Options

Atrazine PendimethalinSimazine KerbBalan DimensionXL BensulideTeamPro PennantSurflan GalleryBarricade Devrinol

Repeat Applications - Summer

• Space 8 to 10 wks apart

• Apply 1/2 X fb 1/2X

• May improve control of crabgrass and goosegrass

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

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

Annual bluegrass

• Winter annual

• Germinates 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

Preemergence Herbicides

• Need rainfall or irrigation (1/2 inch)

• Do not control emerged weeds

• Granular or sprayable

• Most available on dry fertilizer carriers

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

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 required

• Uniform particle size is important

• Release characteristics of fertilizer product

• Control equivalent to sprayable and granular products

Preemergence Herbicides - Formulation Effects

Barricade lbs. ai/acreSmooth 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/acreSmooth

Crabgrass Goosegrass1EC 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/acreLarge

Crabgrass Goosegrass1EC 0.25 + 0.25 88 72

18-3-12G 0.25 + 0.25 96 94

Johnson and Murphy, 1991

Weed Life Cycles

• Summer annuals - < 1 yr.

• Winter annuals - <1 yr.

• Biennials - 2 yr.

• Perennials - > 2 yr.

Weeds can be a problem in all 12 months.

What is the best preemergenceherbicide for turfgrasses??

It depends……….

Preemergence Herbicide Selection

• Turfgrass species

• Weed species

• Immature vs. established

• Time of year

• Irrigation capabilities

• Renovation plans

Preemergence Herbicide Selection

• Granular or spray equipment

• Desired control level

• Application frequency

• Ornamental tolerance

• Cost??

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!

Lack of Preemergence Herbicide Performance

• No rainfall or irrigation

• Excessive rainfall shortly after application

• High rainfall year

• Poor site drainage

• Drought

• Rate too low

• Mow/Bag before incorporation