wide world of weeds, dr. ron strahan, lsu agcenter
TRANSCRIPT
Some reasons weeds are
problems?1) Reduce yields of crops – harvest efficiency
2) Reduce land use efficiency
3) Spoil beauty of turf and ornamental areas
4) Diminish enjoyment of outdoor recreation
5) Can cause allergic reactions due to toxicity
Why so many weeds? – Pigweed
example
13,000 – 100,000 seed/year
Dormancy – survive 30 years
Don’t allow seed production
How are weeds able to persist?
1) Number of seed produced
2) Survival of weed seed
3) Dormancy
4) Vegetative reproduction
How do weeds spread?
1) Nature
Animals and birds – Chinese tallow tree
Winds – dandelion
Rains and flooding
Some type of runner – rhizome, stolon
2) Humans
Impure seed/sod – contaminated wildflower
Compost and mulch – animal droppings
Irrigation – wet areas for sedges
Machinery – contaminated mowing equipment
Contaminated soil
Types of Weeds• Broadleaves –
– Netted veination
– 2 cotyledons
– Taproot
– Showy flowers
• Grasses –– Parallel
– 1 cotyledon
– Fibrous roots
• Sedges –“nutgrass”
– Triangular stems
– Leaves in 3’s
Virginia
buttonweed
Crabgrass
purple nutsedge
Types of Weeds
• Annual and perennial summer weeds
• Annual and perennial winter weeds
Goosegrass (a) Virginia buttonweed (p)
Burweed (a)
Crabgrass (a)
Annual
bluegrass (a) dandelion (p)
Weed Control in Lawns
Most important concept in weed control
is proper turfgrass management
Thin Turf = Weedy Turf
Indicator Weeds
Soil condition Indicator weeds
soil compaction
goosegrass, Poa
low nitrogen clovers
poor drainage
Dollarweed, sedges,
doveweed
drought Dallisgrass, bahiagrass
Weed Control in Lawns
• Before you spray a herbicide – you need a basic knowledge of lawns and weeds
• Improper applications can be very costly
• Spray wrong herbicide on turf
• Equipment not calibrated
• Did not read label
Choosing the right turfgrass
species
• Purpose of turf – plans for area
• Match grass with growing area
– Shade
– Soil type
– Traffic
– High maintenance vs. low maintenance
Proper Management First
• Choose the right grass species
• Mowing and fertilizing
• Traffic control
• Control diseases and insects that weaken
turf
• Applying irrigation properly
Mowing Heights
• St. Augustinegrass - 3”
• Zoysiagrass - 1 to 2”
• Centipedegrass - 1 1/2 to 2”
• Bermudagrass - 3/4 to 1.5”
Definitions
• Active ingredient – molecule that
provides herbicidal action
– Glyphosate – Roundup, Eraser etc
– Trifluralin – Preen, Treflan
• Mode of action – physiological process
that leads to negative plant effects
– Photosynthesis inhibitor - Atrazine
– Mitosis disruptor – Preen
– Amino acid production disrupted - Roundup
Types of Herbicides
• Preemergence – Weed preventor/residual
herbicides – controls weeds before you
see them
• Postemergence – kills weeds that are
actively growing
Effective Preemergence
Application
• Apply before weeds germinate
• Adequate rainfall or irrigation is needed
• Do not expect all season control - reapply
Crabgrass
• Summer annual
• Produces lots of seed
• Germinates - soils reach 53 - 58F
• Light is required for germination
Goosegrass
• Summer annual
• Produces lots of seed
• Germinates - soils reach 60-65F
• Light is required for germination
When to apply preemergence
herbicide in turf
• Summer Weed Control- Around March 1 in North LA
Scotts Halts
Green Light Crabgrass Preventer
Hi Yield with Dimension
• Winter Preemergence – apply toward the end of September or early October
Types of Herbicides
• Nonselective – kills everything -
Roundup, Finale
• Selective – controls certain plants and
releases other species – Weed-B-Gone,
Vantage, Atrazine
What determines selectivity?
• Time of application
• Rate of application
• Chemical, biochemical, morphological or
physiological differences
Knowledge of when and how to use
herbicides
Types of Herbicides
• Contact – burns back what only what it
hits - Diquat, Finale
• Translocating (systemic) – move
throughout plant – Weed-B-Gone,
Vantage, Roundup
Roundup
• Active ingredient – glyphosate
• Will kill or injure most plants
• A systemic herbicide – good on perennial weeds
• Totally deactivated when it hits soil
• Visual symptoms in 2-4 days in growing points
• Find everywhere
Postemergence Facts
• Easier to control small actively growing weeds
• Some temporary injury to turf
• Greater turf injury at high temps (> 85F)
• Few options for St. Augustinegrass - very injury
prone
Bad Times to Apply Herbicides
1) Transition periods for lawns
2) Drought stressed periods
3) Newly sodded, sprigged, or seeded turf
4) Increased injury to turf when temps are above 85 F – some herbicides are volatile
5) When you did not read the label
What’s on Label
1) Type of formulation – L, DG, WP, DF
2) Use classification – general use vs restricted
use
3) Common and chemical name
4) Precautionary statements
Proper Pesticide Use
1) Read label – label tells how to use and precautions
2) Store properly
3) Never eat or smoke near chemicals
4) Wear protective clothing
5) Use correct rate (calibrate)
6) Avoid drift and water contamination
7) Triple rinse containers
IPM
Takes into account all disciplines that affect
plant health
Make treatments when pest reach
unacceptable levels – monitoring is necessary
Object – not to eliminate pest but keep
populations below damaging levels
Pesticides and the
Environment
Master Gardeners have a unique
opportunity to educate others about
proper pesticide use and the environment
Reducing plant stresses reduces pesticide
loads on the environment
Steps Applying Preen/Amaze etc. –
Existing Bed
1. Remove existing weeds by hand
2. Sprinkle granules as directed over
existing landscape plants and on top
of old mulch – water in
3. Do not expect all season control -
reapply
Steps for Pre application – new bed
1. Prepare flower bed
2. Transplant landscape plants and water
3. Sprinkle herbicide granules as directed
over new landscape plants – rinse off
4. Apply mulch
5. Do not expect all season control - reapply
Consumer Preemergence
Herbicides for Flowerbeds
• Preen – active ingredient is dithiopyr now
• Amaze – benefin + oryzalin
• Hi-Yield with Dimension – dithiopyr
Work extremely well and very safe
Preemergence Herbicides – Will
not work on …..
• Bermudagrass
• Torpedograss
• Florida Betony
• Chamberbitter
Chamberbitter
• Summer annual
• Vietnam
• Reproduces by seed
• Each fruit contain 6 seeds
• Very common in flower beds
Chamberbitter – what do you do?
• Light is needed for germination
• Add thick mulch in March
• Keep it hand pulled
Florida Betony Staychis floridana
• Perennial plant
• Square stem
• White to pink flowers
• Reproduces quickly by tubers
• Smells like an ashtray
Control? Florida Betony Staychis floridana
• No selective post control in landscapes
• No preemergence
• Weed fabric not effective
• Non-selective herbicides
• WIPE with Roundup
• Apply Bobcat
Control Grasses in the flowerbed
• Vantage - sethoxydim -
• Hi-Yield Grass Killer- sethoxydim – up to 3 oz/gallon – can be used in vegetable gardens
• Ferti-lome Over the Top II – is now sethoxydim – also can be used in vegetable gardens
• Grass B Gon RTU – same as Fusilade – ready to use
These herbicides work well on most summer grasses except……
Image• Pretty good on sedges (nutgrass)
• Active ingredient – imazaquin
• 3.75 oz/gallon
• Dollarweed – very slow
• Landscape uses
• Safe on all warm season turf
• Image has become a brand –use the imazaquin active ingredient
Sedgehammer (halosulfuron)
• Also called Monterey Sedge Killer
• Purple and yellow nutsedge
• Safe on all warm season turf
• Available in consumer packets for 1 gallon of spray material
• May be applied around woody ornamentals
Sedge Control in Lawns and
Landscape
• Sedgehammer Herbicide - Best sedge activity available to homeowners – safe for the lawn
• Sedgehammer Herbicide - can be applied around woody ornamentals
• Image Herbicide- Good on sedges plus some broadleaf activity – several tolerant ornamentals in landscape beds – safe for the lawn
• Indian Hawthorne, gardenia, asiatic/confederate jasmine
Holly (several), Juniper (several), red crape myrtle, liriope, mondo, Hosta
Winter Broadleaves
• Bedstraw
• Black medic
• Common
chickweed
• Henbit
• White clover
• Lawn burweed
Broadleaf Weed Killers – For Homeowners
• 2,4-D, Mecoprop, Dicamba
• Watch the hot weather on St. Aug – spot treat
• Don’t expect Virginia buttonweed control
• Excellent on winter broadleaves
2,4-D
• Broadleaf weeds only
• Can be tough on Centipedegrass and St. Augustinegrass – very tough in hot weather
• Watch out for tomato and okra – very sensitive
• Fair on buttonweed
• Poor on mature lawn burweed (sticker weed) and white clover
Weed B Gon
• Ortho
• 3 way herbicides
• Easiest on turfgrass – go with this one if it is 90F
• Low % of 2,4-D
• Excellent for winter broadleaves
Weed Free Zone
• Ferti-lome
• 3 way plus carfentrazone
• Decent St. Aug tolerance
• Available at nurseries and feed stores
• Same strength as professional Speedzone
Atrazine consistently out-
performs other herbicides on
winter weeds
*Safe for St. Augustinegrass, centipedegrass, zoysiagrass
and dormant bermudagrass
*Be careful with newly planted shrubs – less issues with
established trees
Lawn Burweed – sticker weed
•Treat in February and
March
•Too late in April and
May
•Atrazine, Weed B
Gon, Weed Free
Zone
Clover Options
• Atrazine is unbeatable for winter weed control
• Weed B Gon
• Bayer Broadleaf Weed Killer – St.
Augustinegrass Formula
• Ferti-lome Weed Free Zone
Dollarweed
• Perennial
• Indicates wet areas
• Reproduces by seed
and rhizomes
1. Atrazine
2. Weed Stop 2X
3. Ortho Weed B Gon
4. Ferti-lome Weed Free
Zone
5. Scott’s Bonus S – Weed
& Feed
Weed and Feed
• Careful around flower beds shrubs
• Don’t always perform well in our experiments
• Prefer addressing fertilizer/weed problem
separately
• Late-March to April timing
Vantage / Poast or Hi-Yield Grass Killer
• Sethoxydim – active ingredient
• Use in Centipedegrass only – no other southern turf is tolerant
• Good on bermudagrass
• 1 oz per gallon but centipede will tolerate higher
• Annual bluegrass not controlled
Torpedograss Suppression in
Centipedegrass
Latest LSU Research – 3 applications of
Vantage (sethoxydim) spaced 28 days
apart - suppression
Virginia Buttonweed
• Tolerates low mowing
• Highest seed germ
at 86 F - July
• Reproduces by seed – 2 seed in every capsule (above/below ground)
+ stem fragments etc.
• Number 1 weed in South
Weed Free Zone
• Ferti-lome
• 4 way herbicide that contains carfentrazone
• Decent St. Aug tolerance
• Same strength as professional Speedzone
• Decent but not great VBW control – 2 applications needed
• Rate = 1.5 oz/gallon
VBW Consumer Herbicides
1. Manor – 80%
2. Weedfree Zone – 60% - 2 shots are needed for long term control
3. Weed Stop 2X – 45%
4. Weed B Gon – 40%
5. Weed B Gon Max – 35%
6. Bayer Southern – 30%
7. Southern Ag Trimec – 30%
Dallisgrass
• Perennial - stubby rhizomes
• Common throughout the south
• Tolerates low mowing and drought
• Fairly cold tolerant
Dallisgrass Control
• Vantage –
centipedegrass
• MSMA – now very
limited use
bermudagrass
• Roundup – St.
Augustinegrass
Best Brush Killers – contain triclopyr
• Ortho Poison Ivy and Brush Killer, Hi-Yield , Bayer Brush Killer – contains about 8% triclopyr
– Briars
– Woody plants
– Usually 4 to 8 oz per gallon of water
• Triclopyr - be careful with woody roots
– Can be absorbed by bark on trunks!!!
Poison Ivy
• Perennial
• Reproduces by seed
• Has some look-a- likes
• Roundup, Brush-B-
Gone, Greenlight Cut
vine and stump killer
Fingers 3 turn and flee…..fingers 5 let it thrive
Use Triclopyr for unwanted trees and vines with the cut
stump method (Greenlight Cut-vine and Stump Killer or Brush B Gon)
Cut unwanted vine or tree with loppers and treat fresh cut with triclopyr
Glyphosate with 41% active
• Roundup, Hi-Yield Killzall, Eraser, Eliminator etc.
• Will kill or injure most plants
• A systemic herbicide – good on perennial weeds
• Totally deactivated when it hits soil
• Visual symptoms in 2-4 days in growing points
Roundup Brands
• 18%, 41%, 50% glyphosate
• Ready to use products also – usually < 2%
• Roundup Extended – Contains diquat and imazapic – Around trees
– Patios – bricks and driveways, gravel areas
– Do not spray in flower beds
• Prone to drift with high pressure and windy conditions
Rubber Glove/Cotton Glove
• 4 oz glyphosate in 32 oz water
• Rubber glove inside cotton glove
• Dip and squeeze off excess
• Use ungloved hand to remove desirable foliage
• Gently wipe weed leaves
Perfectly Natural - Organic
• 90% vinegar and 8% clove oil
• RTU – no mixing
• Smells good
• Tried it – works well on small annuals
Preen Organic Corn Gluten
• 100% granulated corn gluten meal
• Apply 5 lbs. per 250 sq. ft. (25' x 10') to flower bed
• gluten releases an enzyme that interferes with germinating seeds
• Gave fairly good weed control for 20 days in an experiment
What can I do right now?
• Carefully spot apply broadleaf killer to lawn
• Clean out flower beds and apply Preen, Amaze,
etc.
• Spot treat with Roundup
• Kill vines with cut stem treatment