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Turfgrass Herbicide 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
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
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
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
Bentazon
Basagran T/OAll warm- and cool-season turfgrassescontact, foliage absorbedlimited translocationcan move in xylem if root absorbedinhibits photosynthetic electron transport
BladexBladexCotoran
Source: W. K. Vencill, UGA
Injury Symptoms-Photosynthesis Inhibitors
Oxadiazon
Ronstarall turfgrasses, except centipedereadily shoot absorbed, less so by rootscan be foliage absorbed, “contact burn”does not significantly translocateMOA is related to photosynthesis, light requiredinhibits key enzyme in chlorophyll synthesis,
toxic radicals formed, disrupts cell membranes
Amino acids
Building blocks of plant proteinsEnzymes mediate biochemical
reactionsStorage roles - seed reservesStructural roles
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, Manage,TranXit, Monument, Revolverrapid shoot and root absorptiontranslocates to meristematic areasinhibits leucine, isoleucine and valine synthesisgrowth 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 absorbedextensively translocated in phloem inhibits tryptophan, tyrosine and phenylalanine synthesisgrowth 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 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
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
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-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
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 - Fusliade 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 Inhibitors
Aryl-oxy-phenoxiesfenoxaprop - Acclaim Extra
used on cool-season grasses and zoysiagrass
fluazifop - Fusilade IIUsed only on tall fescue and bermudagrass
diclofop – IlloxanUsed 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, CAMAfoliage absorbedextensive movement in xylem and phloeminterfere with ATP productionalso interfere with enzyme activity and cell
divisionUsed 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
TurfWeedManagement
georgiaturf.com