Presentation on theme: "Turfgrass Herbicide Mode-of-Action Tim R. Murphy The University of Georgia."— Presentation transcript:
Turfgrass Herbicide Mode-of-Action Tim R. Murphy The University of Georgia
Mode-of-Action - The entire sequence of events 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. Example 2,4-D will control many broadleaf weeds without seriously affecting turfgrasses.
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 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. Herbicide Movement in Plants
Plant leaf cuticle.
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 CO 2 + H 2 O + Sunlight = C 6 H 12 O 6 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
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 Source: W. K. Vencill, UGA Injury Symptoms- Photosynthesis Inhibitors
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
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, 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
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 pendimethalin on zoysiagrass Dimension on bermudagrass Surflan on St. Augustinegrass 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 Damage occurs within hours. Membrane destruction. No redistribution Complete coverage for kill. Finale on zoysia Finale, Reward, Paraquat
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.
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
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 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)
Source: W. K. Vencill, UGA “rotted” meristem
Organic Arsenicals MSMA, DSMA, CMA, CAMA foliage absorbed extensive movement in xylem and phloem interfere with ATP production also interfere with enzyme activity and cell division 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