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Basics of Turfgrass Weed Management. Tim R. Murphy Crop and Soil Sciences The University of Georgia. What is a Weed?. A plant out of place A plant whose virtues have yet to be discovered A flower in disguise. Is this plant a weed???. Common ragweed decreases crop yields, allergen

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basics of turfgrass weed management

Basics of Turfgrass Weed Management

Tim R. Murphy

Crop and Soil Sciences

The University of Georgia

what is a weed
What is a Weed?
  • A plant out of place
  • A plant whose virtues have yet to be discovered
  • A flower in disguise
is this plant a weed
Is this plant a weed???
  • Common ragweed
    • decreases crop yields, allergen
  • Poison ivy
    • skin rashes, fruit consumed by birds
  • Tall fescue
    • desirable turf and forage grass
    • a weed in warm-season turfgrasses

Human beings decide which

plant is a WEED!!!!

why are weeds an annual problem
Why are weeds an annual problem?
  • Seed and vegetative structure dormancy
  • Prolific seed producers
  • Spread of seed
weed seed survival insured by
Weed seed survival insured by:
  • Hard seed coat (testa)
  • Deep burial
  • After ripening mechanisms
  • Germination inhibitors

Weeds are prolific seed producers.


Broadleaf plantain 36,000

Lambsquarters >30,000

Crabgrass 53,000

Texas Panicum 23,000

Annual Bluegrass 2,000


Weeds - Nutsedge



1 ft.



3,000,000 Plants

4,000,000 Tubers



introduced weeds
Introduced weeds
  • Johnsongrass
  • Common lespedeza
  • Crabgrass
  • Broadleaf plantain
  • Water-hyacinth
factors affecting seed germination
Factors affecting seed germination
  • Oxygen
  • Light
  • Scarification
  • Temperature
  • Water
control vs eradication
Control vs. Eradication


-Process of limiting a weed infestation to a

level that is economically or aesthetically



-Elimination of all plants and plant parts of

weed species from an area.

  • Compete with desirable plants for sunlight, moisture and nutrients
  • May exert allelopathic effects
  • Reduce yields or quality of harvested product
turfgrass weeds
Turfgrass Weeds
  • Reduce quality

- leaf width, shape, color differences

  • Reduce density

- outcompete turfgrasses, can lead to erosion

  • Decrease aesthetic value or utility of the turfgrass.

- difficult to mow, disrupt uniformity of playing surfaces, safety considerations, attract insects

develop a plan
Develop A Plan
  • Goals
  • Methods
  • Economics
  • Alternatives
  • Benefits
the goal
The Goal

Establish and maintain a high quality, nearly weed-free turfgrass.

integrated weed management
Integrated Weed Management
  • Methods
    • Preventive
    • Cultural
    • Biological – not available in turfgrasses
    • Mechanical
    • Herbicides
preventive methods
Preventive Methods
  • State and Federal laws
  • Weed-free seed, sod, sprigs
  • Weed-free topsoil, topdressing
  • Clean equipment
  • Field borders
cultural methods
Cultural Methods
  • Adapted turfgrasses
  • Fertility
  • Cultivation
  • Water management
  • Insect and disease control
soil fertility effects on weeds
Soil Fertility Effects on Weeds
  • Low N - legumes, mosses, speedwell
  • High P - annual bluegrass
  • High N - common chickweed, ryegrass, annual bluegrass
  • Low soil pH - red sorrel, broomsedge
weeds favored by high soil moisture
Weeds Favored by High Soil Moisture
  • Sedges - purple nutsedge, green kyllinga
  • Rushes
  • Annual bluegrass
  • Mosses, algae
  • Alligatorweed
  • Pennywort
weeds favored by low soil moisture
Weeds Favored by Low Soil Moisture
  • Prostrate spurge
  • Poorjoe
  • Common lespedeza
  • Prostrate knotweed
weeds favored in compacted soils
Weeds Favored in Compacted Soils
  • Annual bluegrass
  • Goosegrass
  • Prostrate knotweed
  • Common lespedeza
  • Path rush
weeds may indicate a nematode problem
Weeds may indicate a nematode problem
  • spurges
  • Florida pusley
  • prostrate knotweed
mechanical methods
Mechanical Methods
  • Mowing
  • Hand removal
why does mowing control tall growing weeds
Why does mowing control tall-growing weeds?
  • Reduces apical dominance of main stem
  • Basal buds initiate growth
  • Continued clipping depletes root carbohydrates
  • Prevents weed seed formation
why does mowing not control low growing weeds
Why does mowing not control low-growing weeds?
  • Primary growing point is located beneath the mower blade.



  • Herbicide – a chemical used to control, suppress or kill plants.
  • Preemergence – applied before weed seeds germinate
  • Postemergence – applied to emerged weeds
  • Turf species vary in tolerance
  • Weed species vary in susceptibility
  • Turfgrass species and weed identification is critical to herbicide selection!!!!
maintain healthy turfgrass
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 !
  • Use the best species and cultivars for your location
identify the weed problem
Identify the Weed Problem
  • READ textbooks and periodicals
  • Keep a diagnostic tool kit - hand lens, etc.
  • Know the life cycle of the pest (What temp. does a specific weed seed germinate?)
  • Is the weed the cause or effect of the problem?
  • Confirm your diagnosis
weed thresholds
Weed Thresholds - ??
  • Site - putting green, lawn, etc.
  • People - expectations
  • Weed - population dynamics
  • Budget - dollars
scouting sites
Scouting Sites
  • Use zig-zag pattern
  • Make random stops
scouting sites46
Scouting Sites
  • Identify weeds and life cycle
  • Record observations by area

- ornamental beds

- turfgrass areas

* front lawn

* back lawn

scouting sites47
Scouting Sites
  • Record density by species
  • Low - 1 to 10%
  • Medium - 11 to 20%
  • High - > 20%
when to scout
When to Scout?
  • Mid-winter months - winter weeds
  • Late-April to July - summer weeds
  • Late summer - assess summer program
  • Late spring - assess winter program
developing a weed management program
Developing a Weed Management Program
  • Prevent weed introduction
  • Properly maintain turfgrasses
  • Identify weeds and learn life cycle
  • Initiate control practices
    • Preventive
    • Cultural
    • Mechanical
    • Herbicides