Growth Regulator Herbicides Dicamba Injury to Corn · with Herbicide Mode of Action? “Hey Joe,...
Transcript of Growth Regulator Herbicides Dicamba Injury to Corn · with Herbicide Mode of Action? “Hey Joe,...
9/22/2015
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Can You Match Injury Symptoms
with Herbicide Mode of Action?
“Hey Joe,
What happened to your field?”
Plan of Action
• The herbicide classification chart is on
page 98-99 of the Weed Guide
• Approach Site of Action from
symptomology point of view
• Relate to plant physiology
Growth Regulator Herbicides
• 2,4-D, dicamba, Stinger, Curtail, Reclaim
• Activity on broadleaf plants
• Most notable for nastic response
– “Pressed close”
– Caused by unequal growth
• Epinasty
– Plant parts curve downward (2,4-D)
• Hyponasty
– Plant parts curve upward (dicamba)
Dicamba Injury to Corn
• Short brace-
roots
• Fused brace-
roots
Growth Regulator Injury
• Onion-leafing
• Buggy-whipping
• Sleepy wheat with
dicamba
• Deformed small
grain heads with
phenoxys
• Witches broom on
broadleaf plants
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Cell Division Inhibitors
• “Yellow” herbicides, trifluralin, Trust,
Prowl, Sonolan
• Activity on germinating grasses and
small-seeded broadleaf plants
• Do not translocate
• Inhibit mitosis
– Chromosomes do not separate
– Cell elongation inhibited
Inhibit Cell Wall Development
• Cell wall strands
develop
perpendicular to
elongation
• Herbicide causes
multidirectional
strand development
Root Injury with Mitosis Inhibitor
• Club-root
• May find
callous ring on
broadleaf
plants at soil
line
• Callous stem
may become
brittle
Trifluralin on Oat
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Lipid Inhibitors
• ACCase inhibitors
• Very Long Chain Fatty Acid Inhibitors
ACCase inhibitors
• Puma, Discover, Poast, Select, Assure II
• “Fops”, “dims”, and now “dens” (Axial)
• Activity on grasses
• Prevent production of membranes
• Major activity at growing point
ACCase Inhibitor Injury
• Meristem dies
• Inner whorl can
be pulled from
the plant
Poast Injury from Off-Target Drift
• Bleached tissue
where whorl
opens
Very Long Chain Fatty Acid
Inhibitors (VLCFA)
• EPTC, Harness, Dual, Outlook
• Activity on grasses and small-seeded
broadleaves
• Affect the formation of cuticle waxes
• Seedling shoot inhibitors
EPTC on Oat
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Chloroacetamide Injury
• Shortened
midvein
results in
heart-shaped
leaves
Amino Acid Inhibitors
• ALS inhibitors
• EPSPS inhibitor
• Glutamine synthetase inhibitor
ALS Inhibitors
• Wide range of products and selectivity
– Sulfonylureas (Escort, Express, Steadfast)
– Imidazolinones (Raptor, Plateau, Assert)
– Triazolopyrimidines (Python, Firstrate)
– Sulfonylaminocarbonyl-triazolinones (Everest)
• Inhibit branched-chain amino acids
• Synthesis of proteins stops
• Growth ceases quickly
• Chlorosis begins at growing point
Red Coloring with ALS Inhibitor
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Steadfast after Organophosphate EPSPS Inhibitor
• Glyphosate
– One chemical, so many products
• Selective to crops and weeds with
resistance
• Inhibit aromatic amino acids
• Growth stops but plants linger
• Shikimate reaches toxic levels, plants die
• Low dose may cause shoot proliferation
or curved growth in broadleaf plants
Glyphosate
Drift
• Chlorotic
streaks near
throat of whorl
Glutamine Synthetase Inhibitor
• Glufosinate, Liberty, Rely, Finale
• Generally non-selective except for
resistant crops
• Non-translocating
• Inhibit nitrogen incorporation into
proteins
• Ammonia toxicity
• Translucent tissue in a day or two
• Wilting in three to five days
Liberty Injury
• Injury progresses to necrosis in a week or less
• May observe strong shadows behind leaves because of translucent symptomology
Photoststem Interactions
Light is necessary for activity
Low light intensity delays activity compared
to bright light
• Photosystem II inhibitors
• Pigment inhibitors
• Photosystem I inhibitors
• PPO inhibitors
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Photosystem II (PS II) Inhibitors
• Atrazine, Sencor, Betanex, Basagran,
Buctril
• Main activity on broadleaf plants
• Some products translocate in xylem (water
stream), others do not move
• Stops energy flow through PS II
• Redirected energy destroys chlorophyll
and membranes
Xylem-Mobile PS II Inhibitors
• Intervienal Chlorosis
• Necrosis beginning at leaf margins on older
leaves
Atrazine on Cocklebur Pigment Inhibitors
• Command, Balance Pro, Callisto, Impact
• Main activity on broadleaf plants
• Soil and foliar activity
• Inhibit carotene that protects the plant
from bright light injury
• Plants can’t protect themselves from
normal energy flow
• Excess energy destroys chlorophyll and,
eventually, membranes
Pigment Inhibitor Symptoms
• Injury usually
on young
tissue first
Callisto Injury to Corn
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Callisto Injury to Corn Photosystem I (PS I) Inhibitors
• Gramoxone Inteon, Reglone
• Not translocated
• Non-selective
• Very quick acting, within hours in daylight
• The herbicide harvests energy from PS I
and hands it to molecules that destroy
membranes
• Cells leak fluids so quickly that tissue
gets watersoaked appearance
PPO Inhibitors
• Aim, ET, Cobra, Reflex, Ultra Blazer
• Most non-translocating
• Spartan, Payload, Valor are xylem-mobile
• Herbicide stops production of chlorophyll
• Chlorophyll precursors go where they
don’t belong in the cell
• Molecules generate energy that destroys
membranes
Cobra Aim
• Similar to non-
translocating PS II
inhibitors, non-
lethal injury is
expressed as very
discrete necrotic
lesions
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Plumbing Analogies for
Photosynthesis Interactions
• PS II – pipes freeze and the house floods
• Pigment – the bucket underneath a leaky
pipe is not big enough to handle the drips
or it also has a leak in it
• PS I – that pesky neighbor kid comes in
with a pail and dumps water in your living
room
• PPO – you put a water feed into your
bedroom and forget to put a faucet on it
Photo and Movie
Acknowledgement
• Agriliance
• Syngenta
• Oregon State University
• Weed Science Society of America
– http://www.wssa.net