Using Pre-emergence Using Pre-emergence Herbicides Effectively – Herbicides Effectively – Herbicide misuse Issues in Herbicide misuse Issues in the Landscapethe Landscape

Ralph E. WhitesidesRalph E. WhitesidesExtension Weed SpecialistExtension Weed SpecialistUtah State UniversityUtah State University

What is a pre-emergence What is a pre-emergence herbicide?herbicide?

Herbicide applied after crop is Herbicide applied after crop is planted but before the weeds planted but before the weeds emergeemerge

Does not work on established Does not work on established perennial weeds or cropsperennial weeds or crops

Requires rainfall or irrigation to Requires rainfall or irrigation to activate the herbicideactivate the herbicide

Timing is Everything!Timing is Everything!

Herbicide on ground & activated Herbicide on ground & activated prior to weed seed germinationprior to weed seed germination

Spray applications of pre-Spray applications of pre-emergent herbicides applied in emergent herbicides applied in the rainthe rain

Irrigation required if no rainfallIrrigation required if no rainfall

Getting it Right!Getting it Right!

Crabgrass in turf pre-emergence Crabgrass in turf pre-emergence control indicatorscontrol indicators

Some use forsythia bloomSome use forsythia bloom Too early – should be forsythia Too early – should be forsythia

petal fallpetal fall Too early run the risk of “break Too early run the risk of “break

through”through”

Getting it Right! (continued)Getting it Right! (continued)

Soil temperature – upper half inch of Soil temperature – upper half inch of soil – early in day, not in sun, measure soil – early in day, not in sun, measure the site you intend to treatthe site you intend to treat

Temperature above 50 °F three Temperature above 50 °F three consecutive days make application!consecutive days make application!

Make split-applications if necessaryMake split-applications if necessary First part of split earlier than a single First part of split earlier than a single

application – second treatment 7-8 application – second treatment 7-8 weeks laterweeks later

Environmental EffectsEnvironmental Effects

Pre-emergence at right time & Pre-emergence at right time & activated usually very good to activated usually very good to excellent controlexcellent control

Must be threshold level of herbicide in Must be threshold level of herbicide in soil to be effectivesoil to be effective

Abnormally high rainfall could dilute Abnormally high rainfall could dilute below threshold level – sandy soil is below threshold level – sandy soil is constant problem – consider split constant problem – consider split applications applications

In CombinationIn Combination

Fertilizer carrierFertilizer carrier Herbicide rate is fixed to fertilizer Herbicide rate is fixed to fertilizer

raterate Sprayed versus spreader Sprayed versus spreader

delivereddelivered Both do a good job if applied in Both do a good job if applied in

time and activatedtime and activated

Target PracticeTarget Practice

Target weed – annual bluegrassTarget weed – annual bluegrass Winter annual – germinates in late Winter annual – germinates in late

summer/early fallsummer/early fall Apply mid-August if germination in Apply mid-August if germination in

SeptemberSeptember Soil temperature – does not germinate Soil temperature – does not germinate

until soil is until soil is consistentlyconsistently below 70 °F below 70 °F Can’t control perennial annual bluegrassCan’t control perennial annual bluegrass

Gallery (isoxaben) Controls Gallery (isoxaben) Controls Perennial BroadleavesPerennial Broadleaves

Used for keeping dandelion and Used for keeping dandelion and clover from re-invading turfclover from re-invading turf

Necessary to control existing Necessary to control existing perennial firstperennial first

What could cause a pre-What could cause a pre-emergence herbicide to fail?emergence herbicide to fail?

1. You failed to read the label1. You failed to read the label2. You disrupted the chemical barrier2. You disrupted the chemical barrier3. Your herbicide combination (or lack 3. Your herbicide combination (or lack

thereof) did not cover a broad weed thereof) did not cover a broad weed spectrumspectrum

4. You failed to incorporate the herbicide 4. You failed to incorporate the herbicide with irrigationwith irrigation

5. You routinely over-watered your plants5. You routinely over-watered your plants

What are 10 reasons that pre-What are 10 reasons that pre-emergence herbicides fail?emergence herbicides fail?

1. You failed to read the label1. You failed to read the label2. You disrupted the chemical barrier2. You disrupted the chemical barrier3. Your herbicide combination (or lack 3. Your herbicide combination (or lack

thereof) did not cover a broad weed thereof) did not cover a broad weed spectrumspectrum

4. You failed to incorporate the herbicide 4. You failed to incorporate the herbicide with irrigationwith irrigation

5. You routinely over-watered your plants5. You routinely over-watered your plants

What are 10 reasons that pre-What are 10 reasons that pre-emergence herbicides fail?emergence herbicides fail?

1. You failed to read the label1. You failed to read the label2. You disrupted the chemical barrier2. You disrupted the chemical barrier3. Your herbicide combination (or lack 3. Your herbicide combination (or lack

thereof) did not cover a broad weed thereof) did not cover a broad weed spectrumspectrum

4. You failed to incorporate the herbicide 4. You failed to incorporate the herbicide with irrigationwith irrigation

5. You routinely over-watered your plants5. You routinely over-watered your plants

What are 10 reasons that pre-What are 10 reasons that pre-emergence herbicides fail?emergence herbicides fail?

1. You failed to read the label1. You failed to read the label2. You disrupted the chemical barrier2. You disrupted the chemical barrier3. Your herbicide combination (or lack 3. Your herbicide combination (or lack

thereof) did not cover a broad weed thereof) did not cover a broad weed spectrumspectrum

4. You failed to incorporate the herbicide 4. You failed to incorporate the herbicide with irrigationwith irrigation

5. You routinely over-watered your plants5. You routinely over-watered your plants

What are 10 reasons that pre-What are 10 reasons that pre-emergence herbicides fail?emergence herbicides fail?

1. You failed to read the label1. You failed to read the label2. You disrupted the chemical barrier2. You disrupted the chemical barrier3. Your herbicide combination (or lack 3. Your herbicide combination (or lack

thereof) did not cover a broad weed thereof) did not cover a broad weed spectrumspectrum

4. You failed to incorporate the herbicide 4. You failed to incorporate the herbicide with irrigationwith irrigation

5. You routinely over-watered your plants5. You routinely over-watered your plants

6. You tried to save a few pennies by 6. You tried to save a few pennies by using a lower herbicide rateusing a lower herbicide rate

7. You failed to use proper sanitation7. You failed to use proper sanitation8. You topdressed fertilizers8. You topdressed fertilizers9. You did not calibrate your 9. You did not calibrate your

equipmentequipment10. You applied herbicides to 10. You applied herbicides to

soil/containers that already had soil/containers that already had weedsweeds

6. You tried to save a few pennies by 6. You tried to save a few pennies by using a lower herbicide rateusing a lower herbicide rate

7. You failed to use proper sanitation7. You failed to use proper sanitation8. You topdressed fertilizers8. You topdressed fertilizers9. You did not calibrate your 9. You did not calibrate your

equipmentequipment10. You applied herbicides to 10. You applied herbicides to

soil/containers that already had soil/containers that already had weedsweeds

6. You tried to save a few pennies by 6. You tried to save a few pennies by using a lower herbicide rateusing a lower herbicide rate

7. You failed to use proper sanitation7. You failed to use proper sanitation8. You topdressed fertilizers8. You topdressed fertilizers9. You did not calibrate your 9. You did not calibrate your

equipmentequipment10. You applied herbicides to 10. You applied herbicides to

soil/containers that already had soil/containers that already had weedsweeds

6. You tried to save a few pennies by 6. You tried to save a few pennies by using a lower herbicide rateusing a lower herbicide rate

7. You failed to use proper sanitation7. You failed to use proper sanitation8. You topdressed fertilizers8. You topdressed fertilizers9. You did not calibrate your 9. You did not calibrate your

equipmentequipment10. You applied herbicides to 10. You applied herbicides to

soil/containers that already had soil/containers that already had weedsweeds

6. You tried to save a few pennies by 6. You tried to save a few pennies by using a lower herbicide rateusing a lower herbicide rate

7. You failed to use proper sanitation7. You failed to use proper sanitation8. You topdressed fertilizers8. You topdressed fertilizers9. You did not calibrate your 9. You did not calibrate your

equipmentequipment10. You applied herbicides to 10. You applied herbicides to

soil/containers that already had soil/containers that already had weedsweeds

Are there cases of Are there cases of herbicide misuse in the herbicide misuse in the landscape?landscape? 2009 example – provided with home owner approval2009 example – provided with home owner approval Homeowner had 5 London Plane (sycamore) treesHomeowner had 5 London Plane (sycamore) trees Fairly large caliper trees when plantedFairly large caliper trees when planted Now 12 years oldNow 12 years old Trees 1, 3, and 5 were being encroached upon by Trees 1, 3, and 5 were being encroached upon by

trees 2 and 4trees 2 and 4 Decided to remove the trees on May 6, 2009Decided to remove the trees on May 6, 2009 Cut the trees down with chain saw, removed the Cut the trees down with chain saw, removed the

stumps and limbsstumps and limbs

Bad DecisionsBad Decisions After trees were removedAfter trees were removed Father-in-law says these will sucker and Father-in-law says these will sucker and

make a mess of the yardmake a mess of the yard We better treat the stumps!We better treat the stumps! I have just the stuffI have just the stuff Returns with container of Tordon 22KReturns with container of Tordon 22K Treats stumps with straight material using Treats stumps with straight material using

a brusha brush 13 days latter the call came to USU13 days latter the call came to USU

What did the yard What did the yard look like in the look like in the beginning?beginning?

What do you tell What do you tell the homeowner the homeowner

now?now?

Some Important FactsSome Important Facts Sycamore trees don’t suckerSycamore trees don’t sucker Sycamore trees do root-graftSycamore trees do root-graft Tordon 22K is highly mobile in plantsTordon 22K is highly mobile in plants Dow says the product likely moved into Dow says the product likely moved into

adjacent trees within 3-5 hours of original adjacent trees within 3-5 hours of original treatmenttreatment

Separate the treesSeparate the trees Picloram can leak out of trees into soilPicloram can leak out of trees into soil Remove soil and cut roots, remove stumpsRemove soil and cut roots, remove stumps

What will happen What will happen to the trees that to the trees that were not cut were not cut down?down?

Three months Three months laterlater

Seven months Seven months laterlater

When can I replant When can I replant some trees?some trees?

Picloram PersistencePicloram Persistence Average field half-life is 90 daysAverage field half-life is 90 days Half-life range is 20-300 daysHalf-life range is 20-300 days Dissipates more rapidly in warm Dissipates more rapidly in warm

moist conditions of the southmoist conditions of the south If half-life is 300 days it may take If half-life is 300 days it may take

more than 3-5 years before it would more than 3-5 years before it would be safe to replant deciduous treesbe safe to replant deciduous trees

Highly leachable in some situationsHighly leachable in some situations

How does this How does this impact my impact my neighbors?neighbors?

Read the LabelRead the Label

Follow label Follow label instructionsinstructions

There is a reason There is a reason why some why some pesticides are pesticides are Restricted in Use – Restricted in Use – this example is one of themthis example is one of them