Turfgrass Herbicide Families & Mode-of-Action Tim R. Murphy The University of Georgia

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

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. Example 2,4-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.

Translocated herbicides move. Contact herbicides do not move in the plant Phloem mobile herbicides move up and down in the plant Xylem mobile herbicides move up in the plant Translocated herbicides move.

Herbicide Movement in Plants Contact Rupture cell membranes. Symptoms appear within hours. Need complete coverage for kill. Xylem Mobile Taken up by primarily by roots. Found in older leaves that are exporting sugars. Do not move downward when foliar applied. Phloem Mobile Move to points of active growth or food storage. Affect shoot tips, young buds and leaves. Can cause contact burn.

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

Photosynthetic inhibitors Atrazine, simazine, Sencor Light and active photosynthesis needed for activity These herbicides interrupt energy flow resulting in free radicals Free radicals react with cell membranes Atrazine on bentgrass

Ethofumesate Prograss cool-season grasses and overseeded bermudagrass primarily shoot absorbed, some by roots not well absorbed after leaf cuticle is formed translocated if root or shoot absorbed appears to inhibit photosynthesis and respiration, not well understood

Bentazon Basagran T/O All warm- and cool-season turfgrasses contact, foliage absorbed limited translocation can move in xylem if root absorbed inhibits 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

Bladex Cotoran Source: W. K. Vencill, UGA

Amino acids Building blocks of plant proteins Enzymes mediate biochemical reactions Storage roles - seed reserves Structural 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, Plateau warm-season grasses, except bahiagrass rapid shoot and root absorption translocates to meristematic areas inhibits leucine, isoleucine and valine synthesis growth is impaired and plants die over 1 to 3 wk period

Image on bermuda

Sulfonylureas Manor, Corsair, SedgeHammer,TranXit, Monument, Revolver, Certainty rapid shoot and root absorption translocates to meristematic areas inhibits leucine, isoleucine and valine synthesis growth is impaired and plants die over 1 to 3 wk period

Sulfonylureas Manor, Blade – warm-season grasses, except bahiagrass; also on Ky. Bluegrass Corsair – Ky. Bluegrass, bahiagrass, bermudagrass SedgeHammer– all warm- and cool-season turfgrasses Revolver – bermuda, ‘Meyer’ zoysia Monument – bermuda, zoysia TranXit – bermuda, zoysia, centipede, overseeded bermudagrass Certainty – bermuda, zoysia, centipede, St. Augustine

Pyrimidunyloxybenzoic Velocity Overseeded bermudagrass rapid shoot and root absorption Translocated via phloem inhibits leucine, isoleucine and valine synthesis growth 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 absorbed extensively translocated in phloem inhibits tryptophan, tyrosine and phenylalanine synthesis growth 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 translocation Inhibit cell division (tubulin formation) Has POST activity on seedling crabgrass Used on most warm- and cool-season turfgrasses

DNA Root inhibition Swollen, club shaped roots Surflan on St. Augustinegrass pendimethalin on zoysiagrass Dimension on bermudagrass Swollen, club shaped roots

Asulam Asulox readily absorbed by foliage, minor root absorption translocates in phloem and xylem inhibits cell division also inhibits RNA and protein synthesis used on St. Augustinegrass and ‘Tifway’ bermudagrass

Pronamide Kerb root absorbed, translocated in xylem controls emerged cool-season grasses inhibits cell division Used 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 activity disrupts electron flow in photosynthesis leads to formation of free radicals which damages cell membranes cellular fluids leak, followed by death used on dormant bermudagrass

Glufosinate Finale readily absorbed by leaves primarily 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 photosynthesis used on dormant bermudagrass

Cell Membrane Disrupters Finale, Reward, Paraquat Finale on zoysia Damage occurs within hours. Membrane destruction. No redistribution Complete coverage for kill.

Organic Arsenicals MSMA, DSMA, CMA, CAMA foliage absorbed Mobile in xylem and phloem Not well understood, rapid desiccation indicates cell membrane destruction Used 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 Ronstar all turfgrasses, except centipede readily shoot absorbed, less so by roots can be foliage absorbed, “contact burn” does not significantly translocate Light required inhibits 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 QuickSilver Contact, quickly absorbed Fast-acting Inhibits 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 Dismiss Root and shoot absorbed Fast-acting Inhibits 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 Drive shoot and root absorbed readily translocates in xylem and phloem MOA not fully understood Broadleaf's - alters auxin levels Grasses - affects cell wall synthesis, increases cyanide and ethylene production Used on tall fescue, zoysia and bermudagrass, Ky bluegrass

Drive on crabgrass, 7 days after treatment

Phenoxy, Benzoic Acid, Picolinic Acid Phenoxies – used on cool- and warm season turfgrasses, except St. Augustine Benzoic acids - used on cool- and warm season turfgrasses Lontrel – all cool- and warm-season grasses Confront – cool- and warm-season grasses, except St. Augustine Turflon – Ky. Bluegrass and tall fescue

Growth Regulator Herbicides Symptomology 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-San Metolachor - Pennant root absorbed, essentially no translocation disrupts cell division and enlargement Metolachor - Pennant mainly shoot absorbed, some root uptake translocates in xylem inhibit root and shoot growth disrupts protein, fatty acid and lipid synthesis

Growth Inhibitors Bensulide - Betasan, Pre-San Metolachor – Pennant Cool- and warm-season turfgrasses Metolachor – Pennant Only on warm-season turfgrasses

Growth Inhibitors Siduron - Tupersan readily absorbed by roots, translocated in xylem inhibits root growth, may disrupt mitosis Used only on cool-season turfgrasses and zoysiagrass

Growth Inhibitors Gallery rapidly absorbed by roots, minimal foliage absorption moves in xylem inhibits cell wall biosynthesis Used 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 Cyclohexanediones sethoxydim - Vantage, Poast used only on centipedegrass and fine fescue clethodim – Envoy used 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-phenoxies fenoxaprop - Acclaim Extra fluazifop - Fusilade II diclofop - Illoxan Rapidly absorbed by leaves, extensively translocated via phloem to meristems, (diclofop translocation is slow) Inhibit key enzyme in fatty acid synthesis

Fatty Acid Inhibitors Aryl-oxy-phenoxies fenoxaprop - Acclaim Extra used on cool-season grasses and zoysiagrass fluazifop - Fusilade II Used only on tall fescue and bermudagrass diclofop – Illoxan Used only on bermudagrass

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)

“rotted” meristem Source: W. K. Vencill, UGA

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