PL SC 352 Midterm 3

Group 3 and 4 Herbicide Properties

Selective grass and broad leaf weed control

Applied to soil (pre-plant incorporated, PPI)

Poor water solubility

Little to no translocation in plant

Adsorb to soil and organic matter

• More tightly held on OM

• Low leaching potential

Can volatize and photodegrade

Degraded by microbial action

Group 3 and 4 Herbicides Mode of Action

Target Site

• Tubulin

  • Microtubules

  • Binds to β-tubulin which prevents polymerization to create microtubules

  • Results in cessation of meristematic cell divisions

• Microtubules functions

  • Cell division: mitotic spindles organize and separate chromosomes

  • Cell elongation: microtubules play active role

Injury to Plants

Lack of cell division – growth

Lack of cell elongation and growth (roots)

Loss of membrane integrity – cell death

Also affects cuticle development

Basis of Selectivity

Unclear basis for selectivity

No differences between monocots and dicots

Possible selectivity based on seed lipid content related to herbicide uptake

Selectivity

In grass, selectivity based on anatomical differences, herbicide placement and seed depth

Mesocotyl elongation in many grass weeds elevates coleoptile node to near soil surface but not in cereals.

• Therefore, most sensitive zone in cereals can remain below the treated soil layer

• Coleoptile not sensitive to DNAs

Auxinic Herbicides: The First Selective Herbicides

2,4-D and MCPA were discovered independently in the UK and USA in the 1940’s

Development of new auxinic herbicides continues as an active research area

Group 4 Auxinic Herbicides

Acts like an uncontrolled auxinic hormone in broadleaf plants – deregulation of growth

Systemic herbicides, weak acids/water soluble

Affect mainly broadleaves but grasses can be affected if applied at some stages

• Selectivity due many factors, differential metabolism, plant morphology

Symptoms include growth deformation, epinasty, leaf cupping

Resistance weeds – very few resistance weeds

Dicamba resistant crops in pipeline

Soil residual activity depends on the rate of degradation by soil microbes – some very long residual, some short

POST emergence for the control of broadleaf weed in grass crops

Soil residual activity varies with individual herbicides

Some are volatile, differ by formulations

• Vapor drift

Translocate from leaves or roots to growing points

Selectivity due to metabolism of the herbicide to a non-toxic form

Uptake and Translocation

Rapid translocation

Weak acid trapping

Phloem translocation

Mode of Action: Deregulation of Auxin Hormone Balance

Auxin (IAA) concentration is a function of synthesis degradation and conjugation

Sites of Action

Not a simple mode action

Duplicate, at least in part, the action of plant hormones that are not well understood

Slow and rapid changes upon application are observed

MOA must account for both

Slow and Rapid Responses

Auxin- responsive genes (AR)

In the absence of IAA, AR genes are repressed by a AUX/IAA repressor protein that sits on the gene

In the presence of IAA, AUX/IAA is degraded by TIR1 (complex) and the gene is expressed

IAA binds to the TIR1 to allow TIR1 to degrade Aux/IAA and allow gene expression

Soil Residual Activity

Short residual products are broken down by soil microorganisms

Long residual products

• The combination of water solubility, and long residual activity mean these herbicides are subject to leaching and off target movement

Kochia Resistance

Is resistant to the group 2s (ALS inhibitors), the group 9’s (glyphosate) and group 4’s (dicamba)

Physical Weed Control

Refers to mechanical or hand controls where the pest is actually attacked and destroyed.

• Tillage, fire, removal by hand, grazing and mowing are all used to destroy weeds and prevent reproduction

• Weeds are not controlled through a single operation

• AB Gov – physical control of pests

Tillage Considerations

Amount of tillage affects

• Weed seed distribution

• Soil moisture and temperature

• Crop residues

• Run-off (fertilizer/pesticides)

Zero till: problem with perennials, volunteer crops, and wind-dispersed seeds

Tilling for perennials – how far do tap roots go down. Can you till that far?

Really early tillage use - seedbed prep

By ~6000 B.C. there are drawings of a Y-shaped branch tipped with bronze.

3000 B.C. – Hand sickle was invented.

1000 B. C. - T-shaped implement pulled by cattle or slaves.

500 B.C. drag harrow from a tree limb with short stubs of branches

1000 A.D – harrow was a A-shaped log with wooden pegs

• Horse collar

Development of ploughs

By 1617 – Wood ploughs with iron-pointed share

Moldboard plough with iron share patented by Thomas Jefferson in 1797

All steel plow by 1837, chilled steel moldboard and shares by 1869

Disk Harrows

Deeper tillage

Works via burying weed seeds. Some weeds have trouble emerging from deeper in the soil profile

Size affects depth

Heavy Tine Harrow

Pulls weeds out of the ground

Shallow disturbance vs discing

Rod Weeder 1912-1914

First tool developed specifically for weed management

Rotary Hoe

Controls early emerged weeds, physically flicking them from the soil

Shallow soil disturbance

Interrow Cultivation

Clearance is important for post-emergence control

Works between rows

Various tools which can fit between rows

Mowing

Can be more labour intensive

Can be used to manage patches

May require multiple passes to control regrowth or later emergence

Mulching

Uses:

• Horticulture

• Greenhouse / Protected Ag

• Field margins or patches

Types:

• Plastic mulch/plasticulture

• Straw

• Hydro-mulch

Straw Mulch

Straw use on strawberries

Absorbs moisture

Modulates soil temperatures

Hydro-Mulch

Used for erosion control and hydroseeding

Plastic Mulch

Different colors and densities

Used commonly with drip irrigation and fumigants

Weeds can occur in planting holes and in breaks in plastic

Evaluation of Physical Control Strategies for Kochia Patch Management

Methodology

• Six treatments

  • Non-treated, mowing, AC Saltlander, Black Plastic, Hydro-Mulch, Chaff

Plastic mulch works best, then chaff, coco mulch and lastly mowing

For HWSC to be effective

Weed seeds must be retained at time of crop harvest

Produced at a height where they will be collected by combine

Able to collect weed with combine

Multiple Methods of HWSC

Narrow windrow burning

Direct bale system

Chaff lining

Chaff cart

Chaff tramlining

Impact mills

Nonselective, non residual herbicide

Since commercial introduction in 1974, glyphosate [N-(phosphonomethyl)glycine] has become a dominant herbicide worldwide

Many uses: Pre-seeding, in-crop (on glyphosate-resistant crops), pre-harvest, no-till fields, complete vegetation in industrial sites, direct spray in orchards, forestry after dormancy

• Glyphosate was a major contribution to reduction of tillage

Non-selection – no metabolized by the crop – kills both broadleaves and grasses

Non-residual – no uptake from the soil, degraded rapidly in the soil by microbial activity

Physical Properties

Zwitterion = Several protons can be disassociated as the pH of the solution changes. + and – charges.

Is a weak acid herbicide

Subject to weak acid trapping

Site of Action – EPSPS – Enolpyruvyl-3-phosphate synthase

The enzyme is part of the shikimate pathway that converts shikimate (a product of the pentose phosphate pathway) to aromatic amino acids

The enzyme is located in chloroplasts (encoded by nuclear DNA)

Glyphosate is structurally similar to phosphoenolpyruvate and binds to the substrate binding site, inhibiting the activity and blocking aromatic amino acid biosynthesis.

Lethality

The shikimate pathway is a major carbon pathway

By blocking EPSPS, shikimate and shikimate 3 phosphate builds up to high amount – over 60% of the carbon can be converted to these compounds in treated plants

Insufficient aromatic amino acid production to maintain necessary protein synthesis

carbon flow to the shikimate pathway results in shortages of carbon for other essential pathways

Glyphosate Resistant Crops

Modified EPSPS with reduced binding affinity for glyphosate (all crops)

Originally in canola, an additional change, glyphosate oxidoreductase (GOX) which degrades glyphosate and reduces the movement to seeds

Group 9 Resistance in Weeds

Introduced in the 1970s

Most widely used herbicide in the world

• Enough glyphosate has been sold in N. America to spray a billion acres

• Used prior to RR crops, pre-seeding, chemfallow

Resistance is due to selection from repeated application

Mechanisms of Group 9 Resistance

Single amino acid changes to the EPSPS reduces the binding of glyphosate to the target site

• Reported in goose grass from Malaysia

• Low level of resistance

  • (≈2 fold)

Altered translocation

Reduced translocation of glyphosate produces PHOENIX morphology

Rapid death of the plant that received the glyphosate

• Regrowth from the balance of the plant

Duplication of the EPSPS gene

Glufosinate

Non-selective herbicide that inhibits glutamine synthetase (GS)

Blocking this enzyme leads to a buildup up of NH3 and glyoxylate

Inhibition of photosynthesis, and a rapid destruction of membranes, cells die rapidly

Not translocated because of rapid effect

Liberty Link crops are resistant because of insertion of pat or bar gene cloned from soil bacterial that metabolize the herbicide

Non-toxic

Group 14 Herbicides

Peroxide Bleaching Herbicides or Protoporphyrinogen Oxidase- Inhibiting Herbicides (PPO)

Light dependent herbicide

Inhibition of Heme and Chlorophyll Biosynthesis pathway

They block Protoporphyrinogen Oxidase (PPO) enzyme by binding with it

The PPO enzyme converts Protoporphyrinogen IX (protogen IX) to Protoporphyrin IX (proto IX)

Heme and Chlorophyll production is stopped

Group 15 - Pyroxasulfone

Herbicides inhibit the synthesis of very long chain fatty acids (VLCFA)

VLCFA are formed in the endoplasmic reticulum

In the absence of VLCFA the membranes become leaky

Pyrasulfotole Uptake and Translocation

Foliar Uptake

Weak acid herbicide with moderate solubility in water

Translocated through phloem and xylem

Translocated to the plant’s meristematic regions.

Inhibits the enzyme 4-hydroxy phenylpyruvate dioxygenase (HPPD)

Action one: cuts off the energy process: (plastoquinone biosynthesis)

Action two: cuts off the vitamin process (α tocopherol biosynthesis)

Action three: cuts off the protective process: (carotenoid biosynthesis)

• characteristic foliar bleaching symptoms

Pyrasulfotole and Bromoxynil - Synergistic Effects

Pyrasulfotole inhibits the HPPD enzyme

• Plastoquinone (PQ) biosynthesis is inhibited

• bromoxynil (Gp. 6) directly competes with PQ for binding in the photosynthetic apparatus

• lower concentration of PQ after pyrasulfotole treatment = better efficiency of bromoxynil

Summary of Group 9 and other herbicides

Glyphosate (Group 9 herbicide) widely used for its multiple uses, low residual activity and non-toxicity

• Resistance in weeds has become an increasing problem

Glufosinate (Group 10 herbicide) is another herbicide inhibiting amino acid biosynthesis (glutamine)

Group 14 and 15 herbicides are soil applied and non-translocated

• Affects heme/chlorophyll (Group 14) and very long chain fatty acid (Group 15) production

HPPD inhibitor (Group 27) e.g. pyrasulfotole

• Used in combination with photosynthesis inhibitor (Group 6)

What is cultural control?

More ‘abstract’ than the other three components of IWM

Management of weeds through use of competition, management of resources, and management of the environment

• Manipulate the crop environment to make it less favourable for weed growth

How do we make a crop competitive?

Seeding rate, seeding depth, fertility, inoculation, seed treatments, variety type, crop type, crop rotation, soil moisture

Plant Competition - What are we looking for?

It is evident that practically all the advantages or weapons of competing species are epitomized in two words - amount and rate

• more rapid and complete germination

• larger, and deeper roots

• larger and rapidly growing leaves

• taller and more branching stems

4R Fertilizer

Right rate, right time, right place, right kind

Some weeds are more competitive for fertilizer than our crops

The Compelling Case for Higher Crop Density

Of 91 cases in the literature in 29 different crops, only 6 failed to show decreasing weediness with increasing crop density

Row Spacing

Data is not as robust in terms of an effect as seeding rate

Difficult to do row spacing side by side

• Packers/soil movement

• Row spacing availability (extremes)

On farm – the row spacing of the seeder is the row spacing of the seeder

• Consideration for purchasing

• Consider row spacing in Europe vs. Canada

New Study - More Diversity

Supplement natural wild oat infestation in fall and spring of the 1st year

Combine optimal cultural wild oat management tactics with truly diverse rotations (not just summer-annuals) under no-till regime

14 Treatments

• 100% herbicide, Chem Fallow and Alfalfa checks

All plots receive a full rate of dicot herbicides

4 x 15 m plots in RCBD with 4 replications

8 locations

The early years - low on the priorities

Primitive agriculture between 15,000 and 10,000 B.C.

Likely no or at least little conscious or intentional practice of weed removal

Agriculture stabilized - move into tillage

By ~6000 B.C. there are drawings of Y-shaped branch tipped with bronze

T-shaped implement pulled by cattle or slave by about 1000 B.C.

500 B.C. drag harrow from a tree limb with short tubs of branches

1000 A.D. harrow was a A-shaped log with wood pegs

• Horse collar

Into the Tillage

By 1617 – wood ploughs with iron-pointed share

Moldboard plough with iron share patented by Thomas Jefferson in 1797

All steel plow by 1837, Chilled steel moldboard and shares by 1869

What was the primary function of ploughs/tillage?

1864

• First chance to not walk

• Two-wheel sulky plough

Number of other agricultural inventions 1870s - 1920s

Not a huge impact on weeds

Steam driven tractors

Hand sprayers

Gas powered tractor

The first chemical control of weeds

What was the first herbicide chemical to be used to control weeds?

• Likely salt, not the first recorded study but first believed herbicide

First studied chemical on record?

• Lime for the control of horsetail in Germany in 1854

Rate and exposure

Concern about the rates of herbicides we use today and exposure of the public to these chemicals

Most chemicals in modern ag are applied at a rate of X g/acre or X mL/acre

Salt heavily used in Kansas 1930s-1950s

• 20 tons/acre

Natural Herbicides

Element based herbicides

Sodium chloride (salt)

Sulfuric acid

Copper sulfate

Iron sulfate

Nitric acid

Other herbicides

Kerosene/gasoline

Sodium chlorate

• Idaho 1927-1935 used 4 million pounds

• Kansas used ~3 million pounds from 1939-1940

Salt of dinitrophenol in 1933 for annual forbs in cereals, onions, peras, and flax

The first “conventional” herbicide

2,4-D

Patented in 1945

Registered in 1947

Still in use today

1950 Conference

The effect of chemicals on wheat: 2,4-D (esters vs amines, sodium salts), oil sprays, 2,4,5-T, methoxone

The effect of chemicals on oats: 2,4-D

The effect of chemicals on barley: 2,4-D

The effect of chemicals on flax: 2,4-D, TCA, MCPA

The effect of chemicals on legumes: 2,4-D, but more diverse chemistries as well

Herbicide Resistance

The inherited ability of a plant to survive and reproduce following exposure to a dose of herbicide normally lethal to the wild type.

• Genetic modification, natural selection, etc.

Herbicide Resistant Crops

Crops not typically tolerant, made tolerant to herbicides

• Glyphosate

• Glufosinate

• Imi (group 2) herbicides

Herbicide Resistant Crop Approvals

Roundup ready soybeans were 1st in 1996

Roundup ready and liberty link canola in 1997

In western Canada primarily RR and LL canola, soybean and corn (southern Prairies and MB)

NOT all GMO (i.e. Clearfield lines are non-GMO, created via mutagenesis)

Not problem free

Problems in Herbicide Resistant Crops

Herbicide resistance

Movement of transgenes/HR traits into weedy relatives

Anti-GMO sentiment

Anti-pesticide sentiment

Regulations

Quick Brief of Biocontrol

Typically biocontrol of weeds means use of pathogens or insects for management

Other biological organisms can be used too

Biocontrol History

First search for biocontrol of weed with insects

• Hawaii in 1902

• Australia in 1914

1920 Cactoblastis cactorum introduced to Australia for the Prickly Pear Cactus

Chrysolina beetle on St. John’s Wort in 1935-1944 (studies as early as the 1920s)

Pathogens for Weed Control

First in 1981 called Devine (for stranglervine control) in the US

• Phytophthora palmivora Butl.

Biomal was the first bioherbicide registered in Canada

• For control of Round-leaved mallow

• Colletotrichum gloeosporiodes f. sp. Malvae

• Registered in 1992, production stopped 2 years later

Shift in market

Harvest Weed Seed Control

A new paradigm of weed control, developed and refined in Australia

Goal: to manage weed seeds still in field at harvest and prevent dispersal

Managing rather than spreading weed seeds at harvest

First tool – not designed for weed control

Genomics

Mapping the DNA of the weed genomes – 31 online to date

Understanding weediness, diagnosing HR, management strategies, etc.

Difficult with complex genome species – wild oat (hexaploidy) – mapped in 2025

Alternative Management Strategies

Current or ongoing innovations

• Weed-It

• Inter-row tillage (old in row crops, new in small grains, oil seeds)

• Clipping

AI involved weeding/robotics

Weed recognition

Information in the Blue Book (crop Protection Guide)

Phone numbers/contacts

Plant staging

How to select a chemical for pest control

Sprayer operations

Mixing order

Pesticides and the environment, container disposal

Safety & PPE

Herbicide group information

Product Selection

How do I remove X weed from Y crop?

• Ex) wild oats from wheat?

Where can we get information on which products are available to us?

• Internet

• Retailer/herbicide company

• Herbicide labels

• Guides to Crop Protection – in Alberta often referred to as the Blue Book

Wild Oats in Wheat Crop

1. Identify the weed of interest (wild oats)

2. Identify the crop of interest (wheat)

3. Choose a viable herbicide option

   • E.g. Axial

Axial (pinoxaden): broad-spectrum annual grass control in wheat and barley crops

And consider whether herbicide resistance may impact your choice

Herbicide Labels

Herbicide labels are the law. Read and follow the label

Contain extensive information about the product and how to use it.

Genuinely helpful information, not only boring legalese.

Health Canada app and website search tool for all registered pesticide products in Canada.

Axial

Label Information:

• Chemical volume: 500 mL/acre (1200 mL/ha)

• Spray volume: 20-40 L/acre (50-100 L/ha) of water volume

Scenario:

• Imaginary Field size: 30 acre (12.1 ha)

• Sprayer tank capacity: 2,000 L

• Spray volume: 40 L/acre (100 L/ha)

• Calc 1: 30 acre x 500 mL/acre = 15000 mL (15 L).

• Calc 2: 30 acre x 40 L/acre = 1200 L (0.6 tanks).

• Calc 3: in the tank, combine 15L chemical + 1185 L water = 1200 L

Boring math but crucial if you want to be a herbicide applicator

Mixing Spray Tank

1. Clean spray tank, ½ fill with clean water, then agitate

2. Add 15 L Axial herbicide (or tank mix, if using) and agitate 2 minutes (e.g. fill with water up to ¾ full)

3. Add correct amount of adjuvant if required (see label)

4. Agitate for 2 minutes, add the rest of the water

5. Spray target area

6. After sitting still or break in spraying, agitate before spraying again

7. Use the spray suspension as soon as it is prepared

8. If an oil film starts to build up in the tank, clean with a detergent

Volume, Speed, Pressure

Volume often specified by the label – adjust the output volume by changing nozzle size, pressure, and speed.

If holding nozzle size constant

• Increased pressure – increased water volume

• Increased speed – decreased water volume

As nozzle opening gets bigger

• Decreased pressure – decreased water volume

• Increased speed – decreased water volume

Rate Controllers

adjust the pressure and herbicide solution output according to speed.

What is drift?

Off target movement of spray droplets.

Reduces weed control in your field.

May damage other crops or plants nearby.

Is a concern when wind too strong – or no wind

Sprayer Settings to Reduce Drift

Create coarser sprays

• Decrease pressure

• Increase nozzle orifice

• Use a low drift nozzle

Protect the spray from the wind (shrouds, keep boom low)

Herbicide Choice

• Use less volatile chemistry on hot days

• Use less potent chemistry on windy days

Watch for Temperature Inversions

Inversion suppresses thermal turbulence

Spray-laden air flows either downhill (like water) or horizontally with light breezes rather than diffusing upward.

Why does droplet size matter?

Does my field have small, dense, hard to hit weeds, or larger, easier to hit weeds?

What nozzles do I have available? What pressure level can my spray system sustain?

What is the risk of drift today (how windy is it)? Are there sensitive crops or habitats nearby that would suffer from drift?

Is there a temperature inversion happening?

Is rain coming? Do I need this herbicide to dry as quickly as possible?

Am I going to use a contact or systemic herbicide?

What is the inhalation risk of this herbicide? (Depends on wind, temperature inversion, humidity)

Application Methods

Application of agricultural herbicides by drone is not yet legal in Canada

• Not on label (legal document).

Major ag company taskforce has been created to work on getting “drone” on herbicide labels. Trials ongoing, some data submitted to PMRA.

Could be extremely useful for industrial vegetation management and/or spot spraying

Applicated Timings of Herbicides

Very Early Season Applications

• Pre-plant incorporation

• Pre-seeding

• Pre-emergence .

Early-Mid-Late Season Applications

• Post-emergence

• Pre-harvest

• Post-harvest

Pre-plant incorporation

applied to soil during tillage

Pre-seeding

applied after tillage but before seeding.

Pre-emergence

applied after seeding but before germination.

Post-emergence

applied once the plants have germinated, varies by crop growth stage and herbicide.

Pre-harvest

applied once the crop is mature, accelerates seed maturation and drying of plants (desiccation)

Post-harvest

applied after harvesting crop, kills translocating perennial weeds and reduces weed seed production

Applications Timing in Practice

A healthy, competitive crop is the most important effective tool against weeds.

Scenario: glyphosate resistant canola.

• Post-emergence: glyphosate - wait until broadleaf weeds are toonie size, wild oats have 2-3 leaves, the better, and canola is around cotyledon stage. In general: the earlier you spray, the better. The smaller the crop plant, the less herbicide it takes up/processes (less stunting).

• Pre-harvest: apply diquat, saflufenacil, or carfentrazone, wait for 50-70% seed color change or until around 20% seed moisture.

• Post harvest: glyphosate, dicamba, 2,4D - spray before freezing. After swathing or straight cutting, allow weeds time to put out a new leaf ¬蚠more susceptible to herbicide uptake.

Western Canada primarily conducts post-emergence applications.

To address emerging weed issues, new products with new modes of action are increasingly designed for pre-seeding and pre-emergence applications.

Consult the Blue Book, agronomists, sales reps, Ag Fieldman, etc. - can help you choose the right herbicide for the right weeds in the right crop at the right time.

Herbicide Record Keeping

Date, rate, crop sprayed, area sprayed (e.g., ha), water vol, nozzle, weather, issues, outcome

Why keep detailed herbicide records? 1) figure out what works, 2) see where you went wrong if application failed, 3) to calculate overall herbicide use and for purchasing in future seasons, 4) proof of application for clients 5) in case of an audit, 6) may be legally required for spraying in certain situations, 7) liability protection

Pesticide Applicator Certification

Available from Lakeland College.

15 applicator classes.

Certification involves a core module common to classes, plus at least 1 specific class. 1 test for the core, 1 test for the license class.

Very common for agricultural, industrial & landscape classes to be taken together.

Need a 70% on each test to pass.

Valid for 5 years - can retake test after expiry or obtain enough credits to ensure certification renewal.

Authorized Assistants (AAs)

Don’t want to become a full Certified Applicator?

Pesticide applicator trainers can provide training & exams to individuals and certify AAs.

Employers often have trainers on staff who can certify their seasonal spray staff as AAs.

AAs may conduct all the same applications as the certified applicator, under direct supervision of that applicator.

Pesticide Application near water

Pesticide use near water is strictly regulated to avoid negative impacts to aquatic ecosystems, irrigation, drinking water, etc.

EPEA prescribes the Environmental Code of Practice for Pesticides:

Spraying within 30 m of open body of water:

• By ground equipment only.

• Do not spray on eroding soil.

• Do not apply within 1 m of water unless specified on label.

• Code of Practice only applies to certain active ingredients (Tables 1 & 2).

• Applies to WCA species, woody vegetation interfering with infrastructure (and recently updated to include FAA species)

• Cannot spray more than 10% of any 100 square meters in the zone 1 – 5 meters from an open body of water for Table 1 herbicides.

• Cannot spray more than 30% of any 100 square meters in the zone 5-30 meters from an open body of water for Table 2 herbicides

Context: spraying aquatic invasive pests in water or large infestations near waterbodies.

Special Use Approvals (SUA) are required for applications within 30 m of an open body of water UNLESS following the Code of Practice.

SUA is NOT needed for cropland, pasture, turf, or landscaped areas.

Pesticide label restrictions about application near water still apply.

Takes about 2 months to obtain from AB Environment – plan ahead.

Deposit of Deleterious Substances Approval required for bodies of water containing fish.

Both applications must be submitted to Alberta Environment & Protected Areas.

The authorized applicator is responsible for determining whether something is an open body of water as defined by law.

Open Body of Water

Includes:

• Lakes, rivers, streams, irrigation canals, and other natural water bodies.

• >0.4 ha on public property.

• >4 ha on private property.

• Vegetation changes, soil changes, or water stain are typically used to define the high water mark.

Does NOT include:

• Ponds or dugouts with no flow onto another property.

• Roadside ditches.

• Dry, intermittent streams less than 0.5 m.

• Stormwater and water treatment systems.

What is herbicide resistance?

The inherited ability of a plant to survive and reproduce following exposure to a dose of herbicide normally lethal to the wild type (WSSA)

Driven by humans or nature

• Human creation by gene modification

• Mutations or existing selectivity to a herbicide

Herbicide Efficacy

• How much herbicide enters the plant cell, and how long does the active form remain available to interact with the target site?

Important First Cases

2,4-D resistant wild carrot (Daucus carota) population discovered in 1957

• First observed case of herbicide resistance

Rigid ryegrass (Lolium rigidum) in western Australia

• Resistant to 11 herbicide groups in 12 countries

• First case of group 2 resistance in 1982

Wild oat (Avena fatua)

• Group 1 resistance discovered in 1988

Kochia (Bassia scoparia)

• Group 2 resistance discovered in 1988

Approximately 11 new unique cases reported annually

Canadian Herbicide Resistance

At least 56 unique cases of herbicide resistance (Heap, 2026)

• Some weeds overlap (i.e. Group 1 & 2 resistant wild oats)

• At least 128 total cases

Most Concerning:

• Kochia (Group 2, 4, 9, 14)

• Wild Oats (Group 1, 2, 14, 15)

• Green Foxtail (Group 1, 2, 3)

• Redroot Pigweed (Group 2, 5, 6)