Herbicide Classification and Mode of Action Classification and Mode of Action Fabián Menalled Land...

Herbicide Classification and Mode of Action

Fabián Menalled

Land Resources and Environmental SciencesMontana State [email protected]

Some Things to Remember….• Photosynthesis (food)• Pigments (energy/light capture)• Respiration (energy)• Amino acids (proteins/growth)• Lipids (cell membranes)• Hormones (growth & development; auxin)

Why Know Herbicide Modes of Action?

• Better understanding of how herbicides perform

• Improve herbicide performance• Diagnose herbicide injury• Prevent and manage herbicide

resistance

Classification can be based on:1. Selectivity, persistence, mobility within

the plant, system, etc.

Herbicide Classification- Selectivity and Persistence -

• Selective Controls or suppresses one species of plant without seriously affecting the growth of another plant species, e.g. 2,4-D

• Nonselective Control plants regardless of species, e.g. glyphosate (Roundup)

• Residual Persist in soil,e.g. aminopyralid – (Milestone), clopyralid (Stinger), and picloram (Tordon)

• Non-residual e.g. glyphosate (Roundup)

Absorption and Translocation

Foliar Contact(Gramoxone)

Root Contact(Treflan)

Phloem (Roundup)

Xylem(Spike)

Xylem and Phloem(Banvel, Tordon)

Rangeland herbicides

Ecosystem

Classification can be based on:

2. Chemical structure or familyacetochlor: 2-choro-N-(ethoxymethyl)-N-(2-ethyl-6-methylphenyl)acetamide

1. Selectivity, persistence, mobility within the plant, etc.

Mode of action = the plant process or pathway inhibited by the herbicide

Contact

Absorption

Toxicity

Translocation

Target Site

Herbicide Mode of Action

Soil applied

Commercial Products (Roundup, Durango)

Mode of Action (Amino Acid Biosynthesis Inhibitors)

Site of Action (EPSPS inhibitor)

Chemical Family (Glyicines)

Active Ingredient (Glyphosate)

Classification byMode of Action

1. Lipid Biosynthesis Inhibitors2. Amino Acid Biosynthesis Inhibitors3. Cell Division Inhibitors4. Synthetic Auxins5,6,7. Photosynthesis Inhibitors9. EPSP Synthase Inhibitor14. Pigment Inhibitors22. Membrane Disruptors16,17,26. Unknown

Including the Group Number on the label is recommended, but not

required, by the EPA

Herbicide Mode of Action Groups

Group 1: Lipid synthesis inhibitors (“grass killers”)

Block ACCase enzyme

Trade Names: Hoelon, Fusilade, Poast, Axial, Puma, Assure

Symptoms

Mechanism of resistance: Altered target site

Altered target site (enzyme)

The normal

situation

A resistant enzyme


Group 2: Amino acid synthesis inhibitors; block ALS enzyme

Trade names: Glean, Telar, Finesse, Muster, Permit, Ally, Escort, Canvas, Finesse, Accent, Basis, Beacon, Exceed, Peak, Matrix, Oust, Maverick, Harmony, Pinnacle, Cheyenne, Reliance, Amber, Rave, Upbeet, Arsenal, Assert, Lightning, Motive, Plateau, Pursuit, Raptor, Sceptor, Broadstrike, FirstRate, StrongArm, Python

Mechanism of Resistance: altered target site

• Translocate to new growth in xylem and phloem

• Plants stop growing shortly after application, but plant death is very slow (10+ days)

Plateau Injury Symptoms

Chlorosis ofyoungest tissue

Stunting

Chlorosis of youngest tissue

ALS Inhibitor Symptoms


Group 4: Synthetic auxins

Overwhelm natural auxin pathways

Trade names: 2,4-D, MCPA, Banvel, Clarity, Milestone, Perspective, Tordon, Stinger, Curtail, Transline, Starane, Garlon, Remedy, Renovate, Paramount, Drive

Mechanism of Resistance: unknown

• Translocate in both xylem and phloem• Symptoms most obvious in new growth• Selectively kill broadleaf plants

• Soil residue varies from a few days to several years

Synthetic Auxin Symptoms

Phenoxy on Red Oak University of Illinois extension

Phenoxy drift on tomatoOhio State University

Benzoic acid on soybean

Photo: HMOA and Crop Injury SymptomsUniv. of Minnesota Extension

Washington State University Extension

Pyrdine on tomato


Twisting needles from drift

Tordon (plicoran) runoff into soybean field

Photo: Kansas State University Extension


Groups 5,6,7: Photosystem II inhibitorsBlock photosynthesis

Trade names: Aatrex, Princep, Simazine, Velpar, Sencor, Hyvar X, Sinbar, Basagran, Buctril, Bronate, Karmex, Direx, Lorox, Linex, Spike

Mechanism of Resistance: altered target site

• Injure old growth first, move only upward in xylem• Injury symptoms: yellowing (chlorosis) of leaf tissue

followed by death (necrosis)

Injury from PSII herbicideInterveinal, tip, and margin chlorosis

Interveinal chlorosis

Leaves necrotic


Group 9: Glycines (glyphosate)

Inhibit amino acid biosynthesis

Trade names: Roundup, Gallup, Kleenup, Landmaster, Pondmaster, Ranger, Rodeo, Touchdown

Mechanism of Resistance: reduced translocation, gene amplification

• Translocates to new growth in xylem and phloem

• Plants stop growing quickly, but plant death is slow (10+ days)

chlorosisshortened internodes

stem proliferation

Glyphosate Injury Symptoms


Group 22: Bipyridiliums (paraquat)

Divert electrons from photosynthesis

Trade names: Reglone, Gramoxone, Scythe, many others

Mechanism of Resistance: enhanced detoxification

• Contact activity only; Doesn’t translocate

• Extremely toxic to animals and humans


Group 22: Bipyridiliums (paraquat)

Symptoms

Other Herbicide Mode of Action Families

Groups 16,17,26: Unknown

Group 3: Microtubule assembly inhibitors

Group 14: Protoxinhibitors

Group 15: Long chain fatty acid synthesis inhibitors

Why Know Herbicide Modes of Action?

Better understanding of how herbicides perform

Improve herbicide performanceDiagnose herbicide injury• Prevent and manage herbicide

resistance

Herbicide Resistance is

The ability of a plant to survive and reproduce after treatment with a dose of herbicide that would normally kill the plant

Is it a serious issue? April 13, 2016: • 467 Resistant Biotypes

• 249 Species (144 dicots and 105 monocots)

• 86 crops in 66 countries

• 157 out to 281 different herbicides

• 22 of the 25 known herbicide sites of action Source: International survey of herbicide resistant weeds

www.weedscience.org

Kochia

R. thistle

Green foxtail

Cheatgrass

Wild oat

Persian darnel

Where do Resistant Weeds Come From?

It’s all about selection…..

When a strong selection pressure is applied consistently, nature evolves rapidly away

Presenter

Presentation Notes

When there’s a heritable trait, such as plant height, that is acted on strongly in a consistent way over time, directional selection drives evolution away from the selection pressure. For example, mowing a population repeatedly can consistently select the tallest plants out of the population, selecting for those plants that are able to maintain their fitness by reproducing at shorter and shorter statures.

When a strong selection pressure is applied consistently, nature evolves rapidly away

selection onextreme

(e.g. mowing)

Trait value (e.g. height)

13 2

Num

. of i

ndiv

idua

ls

Adapted from A. Davis

Presenter

Presentation Notes


Adapted from A. Davis

Presenter

Presentation Notes

Here’s a soybean field on an organic farm up near Rockport. The farmers had contacted me to ask for assistance in managing their out of control giant ragweed population. As a first test, I decided to look at the germination timing of this population, in comparison to a natural streambank population of giant ragweed. Here’s what it looked like. Any guesses as to why this germination profile extends so long into the season? What tool might they have been using? Yes, they were very dependent on repeated cultivation for most of their weed control, and the giant ragweed population had hedged its bets against this stress by having more of the population come up later in the season, after cultivation had stopped.

DNA

Resistance passed on to next generation

Herbicide application: selection pressure for resistant plants

Succeeding generations are also resistant

Herbicide application: selection pressure

Reproduction (sets seeds)DNA mutation: allows resistance

to a herbicide

They’ll come up with a new chemical…right?

Presenter

Presentation Notes

There are 6 big companies doing research and development. There have been no new mode of action chemicals created in the past 20 years. It’s your job to help slow down the pace at which weeds are developing resistance to the chemicals we use. Ok, so how do we do that.

Always rules

In other words…

Presenter

Presentation Notes


Tank Mixes and Evolution of Resistance• Mixing partners

– Different site of action– Similar efficacy and persistence

Assumptions• Target site dominant inheritance • Outcrossing species

Years1 3 5 7 9 11 13 15

% R

esist

ance

0

20

40

60

80

100

Adapted from Powels et al. 1997

A or B used alone

B in rotation

A in rotation

A & B in mixture

In the long term, selection of multiple herbicide resistance

Use herbicides to tune,rather than drive, weed

management system

Davis et al. 2012

Fabian Menalled

719 Leon Johnson Hall

Montana State University

Bozeman, MT 59717

[email protected]

406-994-4783

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Herbicide Classification and Mode of Action Classification and Mode of Action Fabián Menalled Land...

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