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.

Herbicide Classification - Selectivity  Nonselective Nonselective herbicides control plants regardless of species.  Examples Roundup Pro, Finale, Reward, Scythe

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

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

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

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 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.

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

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

Non-Classified Herbicides

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

Turf Weed Management georgiaturf.com