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Herbicides in Forestry

How Herbicides Work

Non-Native Invasive Plants Workshop

Wilkesboro, NC

May 8, 2012

Bill Pickens

Conifer Silviculturalist

North Carolina Forest Service

Outline

• Herbicide Terminology - classifies by

characteristics

• Factors that affect herbicide efficacy

• Herbicide Mode of Action

• Review specific characteristics of some

common forestry herbicides

• Plant physiology, bio-chemistry, agronomy,

research, environmental conditions, plant

identification, safety, certification,

licensing………

• There’s a lot to know

• And they are not created equal

� Terminology for Herbicide Characteristics

• Foliar vs Soil Active

• Herbicides with both are often most effective

• Soil active can be persistent

• Pre- Emergent vs Post emergent

• Selective vs non – selective

• Selective can target specific NNI

� Terminology for Herbicide Characteristics

• Persistent vs non- persistent

• What’s a half life?

• What degrades it?

• How will desirables be impacted?

• Salts vs Ester

• Salts are water soluble

• Salts require a surfactant

• Ester are volatile

• Ester penetrate woody tissue more readily

Active Ingredient

Trade Name

Pre-emer-gent

Post-emer-gent

Selec-tive

Non-selec-tive

Limited mobility

Xylem Trans-located

Phloem Trans-located

Persis-tent

Non-Persis-

tent

Glyphosate Accord x x x x

Triclopyr Garlon x x x x

2,4-D x x x x

Hexazinone Velpar x x x x x x

Imazapyr Arsenal x x x x x x

Metsulfuron Escort x x x x x x

Clopyralid Transline x x x x x

Sulfometuron Oust x x x x x x x

Picloram Tordon x x x x x x

Fosamine Krenite x x x x

Factors that affect Herbicide

Effectiveness

�Stage of growth of plants

�Leaf shape and texture

�Soil – texture, pH

�Plant species (resistant vs. susceptible)

Factors that affect Herbicide

Effectiveness

�Temperature

�Drought

�Soil Moisture

�Rainfall after application

�Light

�Tank mixes and antagonism

�Water quality

Right Herbicide +Timing + Rate

= Success


©Forest Productivity Cooperative

What are Adjuvants???

Answer: anything added to a pesticide spray

mix to increase effectiveness

•Improve --delivery, retention on foliage,

penetration,

Types of Adjuvants

Surfactants- ---chemicals that modify the surface properties of materials they contact

and influence the wetting or spreading of the liquids.

Defoamers --- reduce surface tension of bubbles.

Buffers --- reduce pH of alkaline waters.

Crop oils --- petroleum or vegetable oil based product usually 2% emulsifier and

98% oil added for dissolving waxy surfaces.

Crop oil concentrates---petroleum or vegetable oil based usually 15-20%

emulsifier and 80-85% oil.

Drift Control Agents- reduce spray drift

Penetrants- enhance a liquid’s ability to enter pores or penetrate a surface

Emulsifiers- enable oils to be mixed in water.

You mean herbicides aren’t all the same

How Do Herbicides Work?

� Plants

� Complex organisms: physiological processes

Growth

Development

Photosynthesis

Respiration

Defense

Reproduction

Transpiration

Protein Synthesis

Fatty Acid Metabolism

1000’s more….


� Herbicide Modes of Action

� Disrupt one or more vital processes

• Highly specific

Enzyme

Building BlockBuilding Block



� Disrupt one or more vital processes

• Highly specific

Enzyme

Building Block

Herbicide



� Auxin mimics

• Garlon, Tordon, 2,4-D

� Amino acid inhibitors

• Accord, Arsenal

� Photosynthesis inhibitors

• Velpar, Paraguat

� Mitosis inhibitors (mersitems)

• Krenite

� Cell membrane destroyers

• Paraquat

� Lipid biosynthesis inhibitors

• Poast, Vantage, Fusilade


Imazapyr

� Arsenal AC, Chopper

� Foliar Applications

� Site Prep

� Pine release (fall)

� Cut Stump

� Tree Injection

Imazapyr


� Amino acid inhibitor (branched chain)

� Isoleucine, Leucine, and Valine are not produced

Imazapyr


� Non-selective --(but tolerated

by some conifers)

� Post Emergent

� Control -- broad range of

grasses, broadleaved herbs,

and woody species

� Symptoms appear slowly -- in

youngest leaves first (chlorosis)

� Persistent -- Average soil half

life is 25-141 days

Imazapyr


� Below pH of 5, dry conditions, low temps

� Binds to clay and organic matter

� Very persistent in soil

� Stable in soil for more than a year at normal

temperatures

� Above pH of 5

� It may leach from soil

� more available to the plant

� Degradation is slowed

Glyphosate

� Accord, Roundup, One Step

• Site prep and Release

• Foliar application

• Cut stump

• Tree Injection

Glyphosate


� Amino acid inhibitor (aromatic)


� Non-selective herbicide

� Foliar applications only

� Symptoms first evident on

new growth

• Pigment loss

• Growth stoppage

• Distorted growth

� Fast symptoms, slow death

Glyphosate


� Deactivated by soil, dust

� Post emergent

� Non-Persistent –does not leach

� Absorbed by green tissues only

� Can volatilize on hot days!

Glyphosate

Sulfometuron Methyl

� Oust

� Foliar Spray

� Site prep

� Pine release

� Pre-emergent

� Persistent

� Most effective against grasses

and broadleaf weeds in early

stages of growth

Sulfometuron Methyl

� Oust

� Non-selective

� Accumulates in mersitems

� Symptoms first show 2-3 weeks

after application

� Death (4-6 weeks)

Sulfometuron Methyl

� Oust, Oustar

� Persistent at soil pH > 6.8

� Cold dry conditions after

application slow activity

� Leaches out of soils, especially at

higher pHs

� Usually short-lived in the soil, but

persistence has been observed

under some conditions (2+ years)

Triclopyr

� Garlon, Pathfinder

� Auxin Growth Regulator

� Site prep & TSI

• Foliar application

• Tree Injection

• Cut stump

• Basal bark

� Should not contact pine

foliage, directed

applications only, may

cause temporary injury

Triclopyr


� Selective --effective

against broad leaf species

only, not grasses

� Rapidly taken up by roots

and leaves and

transported to growing

tissues

Triclopyr


� Volatile, high danger of drift

� In the soil, it is rapidly

deactivated, but does not bind

to soil particles

� Usually degrades in 30 days

Picloram

� Pathway, Tordon

� Auxin Growth Regulator

� Site prep and TSI

� Foliar application

� Cut stump

� Basal Bark

� Effective against broad leaf

species only, not grasses

� Taken up readily by roots, less

so by foliage

Picloram

� Pathway, Tordon

� May leach from roots of treated plants

� Readily leaches out of soil, but may

bind to organic matter

� Usually persists in soil for less than 3

months, but organic matter and/or dry

conditions drastically increases half-

life (3+ years)

� Toxic to pines, especially when

stressed

•Cut-stump treatment targeting hardwoods

Read and follow the label!!

Questions?

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