REASONS HERBICIDE APPLICATIONS SOMETIMES...

TVMA Annual Meeting

October 9, 2015

Bill Kline, Dow AgroSciences – Retired

William N Kline, LLC Ball Ground, GA

REASONS HERBICIDE APPLICATIONS

SOMETIMES FAIL

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Solutions for The Growing World

Why Is It Important to Understand Why

Herbicides Sometimes Don’t Work?

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Factors Affecting Herbicide Performance

Controllable

Uncontrollable

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Factors Affecting Herbicide Performance

Controllable

•weed ID – know the target weeds

• plant size and stage of growth

• herbicide selection

• adjuvant/surfactant selection

• water quality

• mixing (compatibility)

• application technique

•weather/environment (somewhat)

• herbicide resistance (somewhat)

Uncontrollable

• weather/environment

• herbicide resistance

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Impacts of Drought:

• Plant reactions to drought are natural and actually work against the efficacy of herbicides

• Cuticle thickness becomes a greater barrier to herbicide entry

• Plant growth slows down – herbicide does not translocate throughout the entire plant: foliage, stems and roots.

Weather

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Plant Responses to Drought

• Stomata on leaf surface close to reduce water loss

> Reduces herbicide uptake

• Leaves wilt, curl, or droop

> Impacts coverage and adhesion

• Leaves may develop thicker cuticle

> Impacts herbicide penetration

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Plant Responses to Drought

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So…….. What to do if you are experiencing drought

conditions?

• First question that we always ask. Is it possible to delay the herbicide

application?

• Sometimes, just wait for a decent rain event.

• Increase herbicide rate

• Increase total carrier volume (water carrier volume)

• Increase or change the surfactant/adjuvant

• Accept less weed control than you expect – this may happen even

with the options above.

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Drought Impacts on Bareground

Rain required to activate

http://www.dowagro.com/vm/

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Impacts of Rain

• Pay attention to weather forecast

• Know capabilities and limitations of herbicides

• Check product information for rainfastness

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Solutions for The Growing World

Improper Weed Identification, Rate,

Application Timing, and Adjuvant

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Misidentification

leafy spurge Canada goldenrod

“But I thought it was…………”

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Identifying Weeds From Pictures

“What is this?”

With camera phones and tablets

weed identification hasn’t become

any easier. Poor focus and lack

of detail on key plant structures

makes ID difficult on uncommon

species.

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Identifying Weeds

Making your pictures count

• Leaf shape and arrangement

• Pubescence, petiole, stem

• Flower detail

Accompanying information

• Location

• Site characteristics (wet or dry)

• Height at maturity

http://www.dowagro.com/vm/

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Proper Plant Identification

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Proper Plant Identification

Walnut Ailanthus

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Application Timing – Label Statements

• “For annual weed control best results are generally achieved when

applied to young, actively growing weeds”

> Germinate from seed , produce seed and die within one year

> Ragweed, pigweeds

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Annual Weeds

Emerge Vegetative growth Flower Mature

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Application Timing – Label Statements

• “For perennial weed control best results are generally achieved when

applied during the vegetative/bud/bloom stage or fall rosette stage”

> Perennial weeds: Emerge from rootstock, produce seed, go dormant (last

more than 2 years)

> Canada thistle, ironweed, dog fennel, woody plants, etc.

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Perennial WeedsVegetative regrowth

after mowing or

development of a

rosette as with thistles,

etc.

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Know Labeled RatesRate

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Know Label Recommendations – read footnotes under tables

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Application Timing

Biggest issues

• Manpower – “we want to target optimum timing but logistics and available

manpower sometimes gets in the way…”

Use Higher Rates; change application method; change herbicide mixtures:

• Hard to control species are prevalent

• Weeds in advanced stages of growth

• Less than favorable growing conditions exist

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Root to Shoot Ratio

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Foliar Applications Too Early

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Foliar Applications Too Late

• Foliar applications lose

effectiveness as the fall season

begins – depends on the herbicide

being prescribed; consider

alternative herbicide mixtures.

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Cultural Considerations

Reduced control may result when

plants:

• Recently mowed, grazed, or cut

(pre or post app)

• Not allowed to re-grow to

recommended stage for treatment

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Use of Adjuvants/Surfactants

Most herbicides require a particular adjuvant, surfactant or diluent.

Generally most important for foliar applications!

• Considerations

> Type of leaf: waxy or hairy

> Leaf interception

> Post-impact drop behavior

• Spend some time learning about these products – lots of changes and improvement in recent years.

• Read product labels for specific adjuvant recommendations

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Effect of adjuvants on droplet behavior on leaves

Waxy leaf

Hairy leaf

Droplet evaporation and spread on waxy and hairy leaves associated with type and concentration of

adjuvants Linyun Xu,a Heping Zhu,b∗ HErdalOzkan,c William E Bagleyd and Charles R Krauseb

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Solutions for The Growing World

Sprayer/Equipment Calibration

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Sprayer Calibration

“Can’t you just tell me how much to put in my 100 gallon sprayer?”

Purpose

• Deliver specified rate per acre

Frequency

• More frequent the better

• Visually check nozzles before every use

• Knowing the nozzle output at a given pressure doesn’t mean it will

always be that way

> Corrosion

> Bad gauges

> Pressure drop between the gauge and the nozzles

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Solutions for The Growing World

Water Quality

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Impacts of Water Quality

• Turbidity – when suspended solids (silt, clay, other organic matter)

floating in water

> Some herbicides bind to particles suspended in water = less available for

target plant(s) example - glyphosate

• Water hardness – all water sources in nature contain dissolved minerals

such as calcium, magnesium, and iron.

> Herbicide molecules attach to positively charged mineral molecules (cations)

in hard water = less available for target plants

> Label should provide warnings if water hardness is a potential problem for a

given herbicide.

• Water pH – very acid or very alkaline water can increase the rate of

herbicide degradation in the tank; generally not a problem in the SE.

Source: Purdue University Extenion,“The Impact of Water Quality on Pesticide Performance” PPP-86

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Solutions for The Growing World

Improper Mixing & Incompatibility

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Mixing Herbicides

• Read label for special instructions

• Check for compatibility

Example from Garlon 3A label: “If tank

mixing with Rodeo herbicide, mix the

Garlon 3A with at least 75% of the total

spray volume desired and ensure that

Garlon 3A is well mixed before adding

the Rodeo to avoid incompatibility.”

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Solutions for The Growing World

What Can Happen During Application

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Impacts of Spray Drift

• Off-target movement of spray

droplets

Non targetDrift

Target Area

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Improper Coverage

• Brush height and density impact volume needed and proper application method

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Inadequate Spray Pattern

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Solutions for The Growing World

When Individual Plant Treatments

Go Wrong

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When Basal Bark Treatments Don’t Work

• Didn’t treat completely around each

stem

• Didn’t treat stem at all (common

problem at higher stem densities)

• Stem too large (or thick corky bark)

• Basal mixture not properly mixed

and agitated

• Exposed roots not treated

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When (Water Based) Cut Stump Treatments

Don’t Work

• Didn’t treat immediately after cutting

> Remember “Seconds Count”

• Didn’t treat entire cambium/outer 2 inches

• Treated cut surface when covered with saw

dust or other debris

• Cut and treated during heavy sap flow

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Cut Stump Treatments

• Treat entire cambium/outer 2 inches of sapwood

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Cut Stump Treatments

• Treat entire cambium/outer 2 inches of sapwood

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When Oil Based Cut Stump Treatments Don’t

Work

• Treated wet bark – turns milky

• Didn’t treat entire cambium/outer 2

inches, exposed bark, & root flares

• Treated cut surface when covered with

saw dust or other debris

• Mixture not properly mixed or agitated

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Hack & Squirt Treatments

• Cuts about 2 inches apart for most species

• Angle cuts downward - 45 degrees

• Cut must penetrate into sapwood

• Fill each cut (about 1 pull) but not to the point of running out of “cup”

• Apply mixture immediately to the cut

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When Hack & Squirt Treatments Don’t Work

• Cut not angled properly to “hold”

mixture

• Cuts too far apart

• Not enough mixture applied

• Cuts not deep enough to allow mixture

to enter cambium/sapwood

• Diluted mixture not properly agitated

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Making a Multi-year Commitment

• Some species require multiyear applications

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Reasons herbicide Applications Sometimes Fail

• Hopefully this review has provided you with some “food for thought” on

things that can go wrong with herbicide applications.

• And, hopefully this review will help you to reduce you chances of

reduced efficacy or herbicide failure.

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Solutions for The Growing World

Questions?

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Solutions for The Growing World

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Low Volume Basal Bark Treatments

• One of the most versatile

treatments

• Performed anytime of year

except when bark is wet

• For trees and brush <6” in

diameter

Autumn Olive, Granite City, IL. Garlon 4 Ultra @ 25% + Bark Oil Blue LT @ 75%

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Hack and Squirt Treatments

Doing a “hack” job

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Coverage

“But then I’ll have to fill up again”• Aerial: 5 gpa

• Ground broadcast: 15 gpa

• IPT and Directed: ?????

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Choosing the Right Broadcast Equipment• Boomless vs. Boom

> Overlaps are of concern for certain brush and tree species

> Some herbicides shouldn’t be overlapped

• Max rate being applied

• Grass damage

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The Following Video Clips come from:

Midwest Area Home / Application Technology Research Unit / Services /

Evaporation and spread of surfactant-amended droplets on leaves

USDA ARS

Heping Zhu

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Recommended Guides Based on Water pH:

• A higher or lower than optimal pH causes some herbicides to begin

degrading

• pH 3.5 – 6 satisfactory for most spraying and short-term (> 1 day)

storage of mixtures

• pH 8-9 adequate for immediate spraying for most herbicides. Most

products mixed in alkaline water should be sprayed the same day.

• Label should provide warnings if pH is a potential problem for a given

herbicide.

Source: Purdue University Extenion,“The Impact of Water Quality on Pesticide Performance” PPP-86

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Cut Surface Treatments

Water Based Treatment

• Applied < 1hr after cutting

•Remember “Seconds Count”

• Can perform all year except during

heavy sap flow

• Apply to cambium/outer 2 inches

Oil Based Treatments

• Applied up to several weeks after cutting

• Perform all year except when bark wet

• Applied to cambium/outer 2 inches,

outer bark, and root flares

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Matching Application Method and Nozzles to Target

Species Height and Density

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Leaf Structure & Terminology