Turfgrass HerbicideFamilies & Mode-of-Action

Tim R. Murphy

The University of Georgia

Mode-of-Action - The entire sequence ofevents that happen from the time the herbicide is absorbed to the eventual plant response (usually death).

Herbicide Mode-of Action

Mode of Action

Three phases* Absorption* Movement to target site* Inhibit biochemical reaction

Herbicide Mode-of-Action

The way a herbicide kills or inhibits the growth of susceptible plants!!

Why understand herbicide MOA?

Better understanding of how herbicides perform.

Diagnosing herbicide injury. Professionalism. Public relations.

Herbicide Classification

Selectivity Herbicide movement in plants Timing of application Chemical Family Mode of Action

Herbicide Classification - Selectivity

Selective controls or suppresses one species of plant

without seriously affecting the growth of another plant species.

Example2,4-D will control many broadleaf weeds without

seriously affecting turfgrasses.

Herbicide Classification - Selectivity

Nonselective Nonselective herbicides control plants

regardless of species. Examples

Roundup Pro, Finale, Reward, Scythe

Xylem - nonliving tissue in a plant that transports water and mineral nutrients from the roots to the shoots.

Phloem - living tissue that transports sugars from the site of synthesis or storage to the site of use.

Phloem mobile herbicides move up and down in the plant

Xylem mobile herbicides move up in the plant

Contact herbicides do not move in the plant

Translocated herbicides move.

Contact Rupture cell

membranes. Symptoms

appear within hours.

Need complete coverage for kill.

Xylem MobileTaken up by primarily by roots.Found in older leaves that are exporting sugars.

Do not move downward when foliar applied.

Phloem MobileMove to points of active growth or food storage.Affect shoot tips, young buds and leaves.Can cause contact burn.

Herbicide Movement in Plants

Mode-of-Action

Retention Absorption Translocation to active cell site Inhibit biochemical reaction Plant metabolism or breakdown

Plant leaf cuticle.

Plant Processes Affected by Turfgrass Herbicides

Photosynthesis Amino acid and protein synthesis Cell division Cell membranes Growth regulation Growth inhibition Fatty acid synthesis

Photosynthesis

CO2 + H2O + Sunlight = C6H12O6

OR

Carbon dioxide + water + sunlight

will yield

Sugar

Triazines

Atrazine – Aatrex, Simazine - Princep Metribuzin – Sencor Used only on warm-season turfgrasses Root and shoot absorbed (except simazine) Inhibits photosynthesis, eventual membrane

disruption, requires light Pre and Post control

Light and active photosynthesis needed for activity

These herbicides interrupt energy flow resulting in free radicals

Free radicals react with cell membranes

Photosynthetic inhibitors

Atrazine on bentgrass

Atrazine, simazine, Sencor

Ethofumesate

Prograsscool-season grasses and overseeded

bermudagrassprimarily shoot absorbed, some by rootsnot well absorbed after leaf cuticle is formedtranslocated if root or shoot absorbedappears to inhibit photosynthesis and

respiration, not well understood

Bentazon

Basagran T/OAll warm- and cool-season turfgrassescontact, foliage absorbedlimited translocationcan move in xylem if root absorbedinhibits photosynthetic electron transport

Photosynthesis Inhibitors

Symptomology Interveinal or veinal yellowing followed

by death of plant tissue from leaf margins inward

POST applications cause rapid browning of plant tissue

BladexBladexCotoran

Source: W. K. Vencill, UGA

Amino acids

Building blocks of plant proteinsEnzymes mediate biochemical

reactionsStorage roles - seed reservesStructural roles

Amino Acid Synthesis Inhibitors

Characteristics Most of these herbicides have soil and foliar

activity except glyphosate Undergo significant translocation Soil residual activity herbicide-dependent Generally, low use-rate herbicides

Amino Acid Synthesis Inhibitors

Symptomology Injury symptoms on grass include stunting, purple

coloration, and inhibited root systems with “bottle-brush” appearance

Broadleaf plant symptomology includes formation of red or purple leaf veins, yellowing of new leaf tissue and blackening of terminal growth

Glyphosate injury includes initial yellowing followed by death of affected tissue

Imidazolinones

Image, Plateauwarm-season grasses, except bahiagrassrapid shoot and root absorptiontranslocates to meristematic areasinhibits leucine, isoleucine and valine synthesisgrowth is impaired and plants die over 1 to 3 wk

period

Image on bermuda

Sulfonylureas

Manor, Corsair, SedgeHammer,TranXit, Monument, Revolver, Certaintyrapid shoot and root absorptiontranslocates to meristematic areasinhibits leucine, isoleucine and valine synthesisgrowth is impaired and plants die over 1 to 3 wk

period

Pyrimidunyloxybenzoic

Velocity Overseeded bermudagrass

rapid shoot and root absorptionTranslocated via phloeminhibits leucine, isoleucine and valine synthesisgrowth is impaired and plants die over 2 to 3 wk

period

Glyphosate

Isopropylamine salt - Roundup Pro , GlyphoMate 41, Razor Pro, Prosecutor

Ammonium salt - Roundup ProDry Diammonium salt - TouchDown Pro

foliage absorbedextensively translocated in phloem inhibits tryptophan, tyrosine and phenylalanine synthesisgrowth is impaired and plants die over 1 to 3 wk period

“dormant” zoysiagrass

Green under “dormant” zoysiagrass

“Dormant zoysiagrass” spot sprayed with Roundup

Cell Division

Plant growth is due to cell division and cell elongation.

Dinitroanilines Benefin - Balan Oryzalin - Surflan Pendimethalin - Pendulum Prodiamine - Barricade Trifluralin - Treflan

Shoot and root absorbed, no translocation Inhibit cell division (tubulin formation)Used on most warm- and cool-season turfgrasses

Dithiopyr

Dimension MOA is similar to dinitroanilines

Shoot and root absorbed, no translocationInhibit cell division (tubulin formation)Has POST activity on seedling crabgrassUsed on most warm- and cool-season

turfgrasses

DNA Root inhibition

pendimethalin on zoysiagrass Dimension on

bermudagrass

Surflan on St. Augustinegrass

Swollen, club shaped roots

Pronamide

Kerbroot absorbed, translocated in xylemcontrols emerged cool-season grassesinhibits cell divisionUsed only on warm-season turfgrasses

Cell Membranes

Contain the cellular contents and regulate the entry and exit of substances that promote or inhibit plant metabolism

Diquat Reward LS

contact, very rapidly absorbed,does not translocate requires light for activitydisrupts electron flow in photosynthesis leads to formation of free radicals which damages cell

membranescellular fluids leak, followed by deathused on dormant bermudagrass

Glufosinate Finale

readily absorbed by leavesprimarily contact activity, limited translocation inhibits key enzyme involved in conversion of ammonia

into amino acids toxic levels of ammonia build up, causes cell membrane

disruption, interferes with photosynthesisused on dormant bermudagrass

Cell Membrane Disrupters

Damage occurs within hours. Membrane destruction. No redistribution Complete coverage for kill.

Finale on zoysia

Finale, Reward, Paraquat

Organic Arsenicals

MSMA, DSMA, CMA, CAMAfoliage absorbedMobile in xylem and phloemNot well understood, rapid desiccation indicates

cell membrane destructionUsed on cool-season grasses, bermuda and

zoysiagrass

Leaf burn on broadleaves and grasses with yellow leaf tips on grasses

Terminal yellowing of grasses

MSMA on zoysia

MSMA injury on tall fescue

Tee infested with Texas sedge

Texas sedge tee after treatment with MSMA

Oxadiazon

Ronstarall turfgrasses, except centipedereadily shoot absorbed, less so by rootscan be foliage absorbed, “contact burn”does not significantly translocateLight requiredinhibits key enzyme in chlorophyll synthesis,

toxic radicals formed, disrupts cell membranes

Oxadiazon (Ronstar)

PRE 2G – Ky. Bluegrass, Bermuda, seashore

paspalum, t. fescue, zoysia, St. Augustine 50WSP – bermuda, St. Augustine, zoysia Annual grasses, selected broadleaves

Ronstar 2G and 50WSP - At Sprigging

Apply immediately before or after sprigging bermudagrass and zoysiagrass

Pre-sprigging (1 day before sprigging slightly safer than post-sprigging)

Irrigate ASAP for best results

Carfentrazone

QuickSilverContact, quickly absorbedFast-actingInhibits enzyme (protoporphyrinogen oxidase) in

chlorophyll synthesis pathway. Leads to formation of toxic intermediates which disrupt cell membranes.

Carfentrazone

Sold with phenoxy herbicides and dicamba as PowerZone and SpeedZone

All turfgrasses does not significantly translocate

Sulfentrazone

DismissRoot and shoot absorbedFast-actingInhibits enzyme (protoporphyrinogen oxidase) in

chlorophyll synthesis pathway. Leads to formation of toxic intermediates which disrupt cell membranes.

Carfentrazone and Sulfentrazone

Carfentrazone – POST, all turfgrassses

Sulfentrazone – PRE, although does have POST activity

Growth Regulation

Naturally produced hormones (auxins, cytokinins, gibberellins, others) are involved in the regulation of normal growth and development.

Growth Regulator Herbicides

These herbicides affect several plant processes such as cell division, cell enlargement, protein synthesis and respiration. They act by upsetting the normal hormonal balance in plants.

Growth Regulator Herbicides

Phenoxys 2,4-D, dichlorprop mecoprop, MCPA

Benzoics Banvel, Vanquish

Picolinic Acids Confront Turflon Lontrel SpotLight

Quinolinecarboxylic Drive

Trimec on bermuda

Phenoxy, Benzoic Acid, Picolinic Acid

readily absorbed by foliage, less so by roots extensively translocated interfere with DNA, RNA and protein

synthesis results in uncontrolled cell division and

elongation vascular tissues are plugged, 1 to 3 wks

Quinclorac

Driveshoot and root absorbed readily translocates in xylem and phloemMOA not fully understoodBroadleaf's - alters auxin levelsGrasses - affects cell wall synthesis, increases cyanide

and ethylene productionUsed on tall fescue, zoysia and bermudagrass, Ky

bluegrass

Drive on crabgrass, 7 days after treatment

Growth Regulator HerbicidesSymptomology

Broadleaf plant stem twisting and curling Leaves on broadleaf plants exhibit

cupping, crinkling, strapping, or drawstring affect

Symptoms on grass plants include leaf rolling, crinkling, brace root fusion and malformation.

2,4-D overdose on St. Augustinegrass

2,4-D Injury on Soybean

Growth Inhibition

Exact MOA not known Inhibit root and shoot growth Disrupt cell division, cell enlargement Also may disrupt lipid synthesis, nucleic acid

and protein synthesis

Growth Inhibitors

Bensulide - Betasan, Pre-Sanroot absorbed, essentially no translocationdisrupts cell division and enlargement

Metolachor - Pennantmainly shoot absorbed, some root uptaketranslocates in xyleminhibit root and shoot growthdisrupts protein, fatty acid and lipid synthesis

Growth Inhibitors

Siduron - Tupersanreadily absorbed by roots, translocated in xyleminhibits root growth, may disrupt mitosisUsed only on cool-season turfgrasses and

zoysiagrass

Growth Inhibitors

Galleryrapidly absorbed by roots, minimal foliage

absorptionmoves in xylem inhibits cell wall biosynthesisUsed on all cool- and warm-season turfgrasses

Fatty Acid Synthesis

Fatty acids are important components of cell membranes

Inhibition fatty acid synthesis blocks production of lipids needed for new cell growth.

Fatty Acid Inhibitors

Cyclohexanedionessethoxydim - Vantage, Poastused only on centipedegrass and fine fescueclethodim – Envoyused only on centipedegrass

Rapidly absorbed by leaves, extensively translocated via phloem to meristems

Inhibit key enzyme in fatty acid synthesis

Fatty Acid Inhibitors

Aryl-oxy-phenoxiesfenoxaprop - Acclaim Extrafluazifop - Fusilade IIdiclofop - Illoxan

Rapidly absorbed by leaves, extensively translocated via phloem to meristems, (diclofop translocation is slow)

Inhibit key enzyme in fatty acid synthesis

Fatty Acid Synthesis Inhibitors - Grass Herbicides

Reddening of leaf tissue.

Discoloration of tissue at and above the nodes.

Tissue and leaves in the leaf whorl can easily be separated from the rest of the plant.

No broadleaf activity.

Fusilade on dallisgrass

Fatty Acid Synthesis Inhibitors

Initial injury in meristematic regions occurs where newest leaves are developing

These regions will turn chlorotic, which is followed by necrosis

The affected area will become “rotted” and will easily separate from rest of plant

Injury will develop slowly (7 to 14 days)

Source: W. K. Vencill, UGA

“rotted” meristem

TurfWeedManagement

georgiaturf.com