3/21/2013. Plan of Action. Growth Regulator Herbicides. 2,4-D on Tomato. Can You Match Injury Symptoms with Herbicide Mode of Action?

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1 Plan of Action Can You Match Injury Symptoms with Herbicide Mode of Action? Hey Joe, What happened to your field? The herbicide classification chart is on page of the Weed Guide Approach Mode of Action from symptomology point of view Relate to plant physiology Growth Regulator Herbicides 2,4-D on Tomato 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) Clopyralid on Canada Thistle Dicamba Injury to Corn Short braceroots Fused braceroots 1

2 Growth Regulator Injury Onion-leafing Buggy-whipping Sleepy wheat with dicamba Deformed small grain heads with phenoxys Witches broom on broadleaf plants 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 2

3 Trifluralin on Oat 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 Diclofop on Wheat and Oat ACCase Inhibitor Injury Meristem dies Inner whorl can be pulled from the plant 3

4 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 Chloroacetamide Injury Shortened midvein results in heart-shaped leaves Amino Acid Inhibitors ALS inhibitors EPSPS inhibitor Glutamine synthetase inhibitor 4

5 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 Chlorsulfuron on Bean Chlorimuron on Cocklebur Red Coloring with ALS Inhibitor Steadfast after Organophosphate 5

6 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 on Cowpea 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 Photoststem Interactions Injury progresses to necrosis in a week or less May observe strong shadows behind leaves because of translucent symptomology Light is necessary for activity Low light intensity delays activity compared to bright light Photosystem II inhibitors Pigment inhibitors Photosystem I inhibitors PPO inhibitors 6

7 Photosystem II (PS II) Inhibitors Xylem-Mobile 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 Intervienal Chlorosis Necrosis beginning at leaf margins on older leaves Atrazine on Oat 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 7

8 Callisto Injury to Corn 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 Paraquat on Bean Paraquat on Corn 8

9 PPO Inhibitors Cobra 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 Aim Similar to nontranslocating PS II inhibitors, nonlethal injury is expressed as very discrete necrotic lesions 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 9