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Turfgrass Herbicide 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
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Turfgrass Herbicide 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
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 Phloem Mobile Move to points of active growth or food storage. Affect shoot tips, young buds and leaves. Can cause contact burn. Xylem Mobile Taken up by primarily by roots. Found in older leaves that are exporting sugars. Do not move downward when foliar applied. Contact • Rupture cell membranes. • Symptoms appear within hours. • Need complete coverage for kill.
Plant Processes Affected by Turfgrass Herbicides • Photosynthesis • Amino acid and protein synthesis • Cell division • Cell membranes • Pigment synthesis (none registered in turf) • 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
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
Bladex Cotoran Injury Symptoms- Photosynthesis Inhibitors Source: W. K. Vencill, UGA
Oxadiazon • Ronstar • all turfgrasses, except centipede • readily shoot absorbed, less so by roots • can be foliage absorbed, “contact burn” • does not significantly translocate • MOA is related to photosynthesis, light required • inhibits key enzyme in chlorophyll synthesis, toxic radicals formed, disrupts cell membranes
Amino acids • Building blocks of plant proteins • Enzymes mediate biochemical reactions • Storage roles - seed reserves • Structural roles
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
Sulfonylureas • Manor, Corsair, Manage,TranXit, Monument, Revolver • 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 • Manage – all warm- and cool-season turfgrasses • Revolver – bermuda, ‘Meyer’ zoysia • Monument – bermuda, zoysia • TranXit – bermuda, zoysia, centipede, overseeded bermudagrass
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
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 Surflan on St. Augustinegrass pendimethalin on zoysiagrass Dimension on bermudagrass Swollen, club shaped roots
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
Carfentrazone • Sold with phenoxy herbicides and dicamba as PowerZone and SpeedZone • Limited translocation • Inhibits key enzyme in chlorophyll synthesis • Causes buildup of phytotoxic compounds which damages cell membranes • Cellular fluids leak, followed by cell death • All turfgrasses
Cell Membrane Disrupters Finale, Reward, Paraquat • Damage occurs within hours. • Membrane destruction. • No redistribution • Complete coverage for kill. Finale on zoysia
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.
Phenoxys 2,4-D, dichlorprop mecoprop, MCPA Benzoics Banvel, Vanquish Picolinic Acids Confront Turflon Lontrel SpotLight Quinolinecarboxylic Drive Growth Regulator Herbicides 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
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 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 • 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
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 - Fusliade 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