YOUTH & FAMILIES AGRICULTURE HEALTH ECONOMY ENVIRONMENT ENERGY COMMUNITIES

Session 4:

Chemical Weed

Control Strategies

Chemical Control Is Often Based On A Herbicide’s:

• Selectivity

- Placement

- Timing

• Mode of action

• Spectrum of

activity

Selectivity Based On Plant Physiology

Causes a toxic reaction

in some plants (e.g., in

broadleaves vs. grasses)

2,4-D

Selectivity Based On Plant Physiology

Causes a toxic reaction

in some plants (e.g., in

broadleaves vs. grasses)

Herbicide blocks an

enzyme used in

amino acid or lipid

synthesis or

photosynthesis

2,4-D

Selectivity Based On Plant Structure

Leaf

shape

Selectivity Based On Plant Structure

Stomata, wax, hairs, or

dust on the leaves all

affect herbicide uptake

Selectivity Based On Application Timing

• Preplant incorporated (PPI)

• Preemergence to crop or weed (PRE)

• Postemergence (POST)

Selectivity Based On Placement

• Depth in soil

– Above crop roots

– Germinating seedlings

absorb herbicide

• Debris on soil surface

can reduce herbicide

effectiveness

Selectivity Based On Placement

• Keep herbicide from touching

desirable vegetation

– Spot spray

– Rope wick or wiper

– Directed sprays

Orchard

application

Herbicide Selectivity Based On Application Rate

Rate Examples

1 pt/acre for annual

broadleaf weeds

Lambsquarters

Mustard

2 qt/acre for perennial

broadleaf weeds

Dandelion

Canada thistle

4 qts/acre for woody

brush and trees

Red alder

Black poplar

Herbicide Mode Of Action

Herbicide Mode Of Action

Herbicide Mode Of Action

Herbicide Mode Of Action

Growth Regulator Herbicides

• Broadleaf weeds

– Can injure grass; depend on stage and rate

• Mimic hormones (auxins)

– Disrupt hormone balance and protein synthesis

– Epinasty (abnormal twisting and bending)

– Affects new growth

• Uptake through foliage

– Move in xylem and phloem

– Soil residual activity

Growth Regulator Herbicides

• Phenoxy Acetic Acids

– 2,4-D; MCPA

• Benzoic Acids

– Dicamba (Banvel)

• Picolinic Acids

– Triclopyr (Garlon)

• Mixes

– Triclopyr + 2,4-D (Crossbow)

Amino Acid Synthesis Inhibitor Herbicides

• Act on enzyme to prevent amino acid production

– Protein for normal growth

• Active on broadleaf and/or grass weeds

– Some give excellent perennial weed control

• Foliage and root uptake, move in xylem and/or phloem

• Injury symptoms slow (1 to 3 weeks)

– New foliage symptomatic first

– Stunting, yellowing or purpling

Amino Acid Synthesis Inhibitor Herbicides

• ALS enzyme inhibitors

– Sulfonylurea

• Rimsulfuron (Matrix)

• EPSP enzyme inhibitor

– Amino Acid Derivative

• Glyphosate (Roundup, Rodeo,

Aquamaster)

Lipid Synthesis Inhibitor Herbicides

• Controls weedy grasses

– Broadleaf plants tolerant

• Prevent fatty acid production for lipids

– Cell membranes and new growth

• Growth points become rotted and easily

removed from rest of plant

• Injury symptoms slow (1 to 2 weeks)

– New leaf tissue yellow or dead

• Foliage uptake, move in phloem

Lipid Synthesis Inhibitor Herbicides

• Aryloxyphenoxypropionate (the “fops”)

– Fluazifop (Fusilade)

• Cyclohexanedione (the “dims”)

– Sethoxydim (Poast), Clethodim (Select)

Seedling Growth Inhibitor Herbicides

• Soil applied

– Act on emerging weed seedlings

– Often die prior to emergence

• Active on developing roots and shoots

– Stops cell division, enlargement, and

protein synthesis

– Inhibit shoot elongation and lateral root

formation

Seedling Growth Inhibitor Herbicides

• Root Inhibitors

– Dinitroanilines

• Trifluralin (Treflan), Oryzalin (Surflan),

Pendimethalin (Prowl H2O)

• Shoot Inhibitors (MOA not completely known)

– Substituted Amide

• Napropamide (Devrinol), Pronamide (Kerb)

Photosynthesis Inhibitor Herbicides

• Bind to specific sites in chloroplasts to shut down photosynthetic process

– Secondary toxic substances likely produced

– Chlorosis then necrosis

• Control grass or broadleaf weeds

• Most are applied preemergence

• Postemergence causes rapid burning

• Grape products are mobile, taken up via roots or foliage and move in xylem

Photosynthesis Inhibitor Herbicides

• Phenylureas

– Diuron (Karmex)

• Nitriles

– Dichobenil (Casoron)

Glutamine Synthesis Inhibitor Herbicide

• Inhibits the enzyme GS

– Glutamine production stops, ammonia builds up

in the cells, leads to chlorosis then necrosis

• For annual weed control; perennials will

regrow

• Absorbed through foliage, no translocation,

not selective

• Organophosphorus

– Glufosinate (Rely)

Cell Membrane Disruptor Herbicides

• Postemergence, contact

• Activated by sunlight to form oxygen compounds

(hydrogen peroxide) which rupture plant cell

membranes

• Symptoms quick (1 to 2 hours)

– Rapid burn-down

• For annual weed control; perennials will regrow

• Grape products are nonselective

Cell Membrane Disruptor Herbicides

• Bipyridyliums

– Paraquat (Gramoxone)

• Diphenylethers

– Carfentrazone (Aim), Flumioxazin

(Chateau), Oxyfluorfen (Goal),

Pyraflufen (Venue)

• Oils and acids

– Clove oil (Matran), Pine oil

(Interceptor), Acetic and Citric Acids

(vinegars, Green Match), Pelargonic

Acid (Scythe)

Pigment Inhibitor Herbicides

• Prevent formation of chlorophyll

– Can’t photosynthesize

– White or translucent leaf coloration

results

• Grape product is mobile, taken up via

roots or foliage and move in xylem

• Pyridazinones

– Norflurazon (Solicam)

Herbicide Mode Of Action

A foliar-applied, systemic, photosynthesis inhibitor (atrazine). It is applied to a leaf, absorbed through the cuticle, translocated to the chloroplasts (site of action), and then inhibits photosynthesis (mechanism of action).

Herbicide Mode Of Action

A foliar-applied, systemic, photosynthesis inhibitor (atrazine). It is applied to a leaf, absorbed through the cuticle, translocated to the chloroplasts (site of action), and then inhibits photosynthesis (mechanism of action).

Herbicide Mode Of Action

A foliar-applied, systemic, photosynthesis inhibitor (atrazine). It is applied to a leaf, absorbed through the cuticle, translocated to the chloroplasts (site of action), and then inhibits photosynthesis (mechanism of action).

Herbicide Mode Of Action

A foliar-applied, systemic, photosynthesis inhibitor (atrazine). It is applied to a leaf, absorbed through the cuticle, translocated to the chloroplasts (site of action), and then inhibits photosynthesis (mechanism of action).

Herbicide Application

• Foliar-applied

• Soil-applied

- Usually requires

incorporation

‣ Water: irrigation,

sprinkler, rainfall

‣ Mechanical:

tillage, raking

Herbicide Precautions, Drift

• Close proximity, downwind

- Sensitive areas

- Wind direction/speed

- Product characteristics (vapor pressure)

• Long distance movement

- Volume applied

- Wind direction

- Surface air stability http://www.cepolina.com

Herbicide Precautions, Drift

• All formulations of

2,4-D and other

growth regulator

herbicides can cause

injury to grapes at

very low levels

– Amine and low

volatile esters

– High volatile esters

are illegal in WA

Herbicide Precautions, Movement in Water

• Lateral movement to neighboring properties

• Vertical movement to groundwater - Label has leaching

statement

- Site vulnerability

- Soil type and moisture content

- Expected rain or irrigation

Herbicide Precautions, Other Factors

• Soil/Plant Material Residuals

- May persist for weeks to years

- Root zones of grape plants

- Downslope movement of herbicides/soils

- Activity in compost or soils

http://blog.vicivino.com

Have You Completed The Four Weed Sessions?

Session 1: Biology of Weeds

Session 2: Weed Reproduction

Session 3: Non-chemical Weed Management

Session 4: Chemical Weed Management