How Herbicides Work. Matt Raymond SCST Superworkshop February 11, 2016

Transcription

1 How Herbicides Work Matt Raymond SCST Superworkshop February 11, 2016

2 Mode of Action vs. Site of Action Mode of Action (MOA) Describes the process within the plant that is inhibited by the herbicide. Another way to think of it is how the herbicide works. For example, amino acid inhibitors are a mode of action that disrupts the formation of amino acids. Site of Action (SOA) Describes the physical location within the plant where the herbicide binds. This can also be thought of as where the herbicide works. For example, within the amino acid synthesis inhibitors mode of action, there are two different site-of-action groups. These are ALS inhibitors and the EPSP synthase inhibitors. Herbicides within these two sites of action inhibit different enzymes within the plant.

3 These numbers refer to the Site of Action (SOA) Group as referred to in the Herbicide Classification Guide. Small arrows show herbicide mobile in system from site of uptake Large arrows indicate placement of herbicide Dots indicate a site of uptake without herbicide translocation

4 Amino Acid Synthesis Inhibitor ALS Inhibitors Blocks the normal function of the acetolactate synthase(als) enzyme, inhibiting plant metabolism. Symptoms Roots may be unbranched and stubby resulting in purple stems and leaves Stunting Leaves turn yellow from outer edge, veins turn light yellow to dark purple Examples STS soybeans Clearfield (IMI) tolerant crops Comments Residual and drift injury are concerns

5 Amino Acid Synthesis Inhibitor ALS Inhibitors Blocks the normal function of the acetolactate synthase(als) enzyme, inhibiting plant metabolism.

6 Amino Acid Synthesis Inhibitor EPSP Synthase Inhibitor - Interferes with the EPSP(5-enolpyruvly-shikimate-3-phosphate) enzyme, disrupts synthesis of essential amino acids. Symptoms Plants turn light green to yellow Stunting Necrosis Examples Glyphosate tolerant crops Comments Drift injury is a concern with spray applications Systemic, moves readily throughout plant

7 Amino Acid Synthesis Inhibitor EPSP Synthase Inhibitor - Interferes with the EPSP(5-enolpyruvly-shikimate-3-phosphate) enzyme, disrupts synthesis of essential amino acids.

8 Growth Regulators T1R1 Auxin Receptors Has activity that is similar to endogenous auxin. Affects growth in the newest tissues by affecting protein synthesis and normal cell division Symptoms Stunted, malformed seedlings New growth twisted or malformed Leaf rolling in grass plants Examples Dicamba & 2,4-D tolerant crops Comments Drift injury is a concern since some chemicals are highly volatile. Equipment contamination

9 Nitrogen Metabolism Inhibitor Glutamine Synthase Inhibitor Inhibits the glutamate synthetase enzyme. Causes ammonia to build up in plant which destroys cells and inhibits photosystem I & II reactions. Ammonia also reduces ph gradient which can uncouple photophosphorylation. Symptoms Yellow and necrotic plant tissue Stunted, necrotic, seedlings in substrate imbibition testing Examples Glufosinate tolerant crops Comments Primarily a contact herbicide, limited translocation from foliar application

10 Nitrogen Metabolism Inhibitor Glutamine Synthase Inhibitor Inhibits the glutamate synthetase enzyme. Causes ammonia to build up in plant which destroys cells and inhibits photosystem I & II reactions. Ammonia also reduces ph gradient which can uncouple photophosphorylation.

11 Pigment Inhibitors HPPD Inhibitor Inhibits a key step in plastoquinone biosynthesis which indirectly inhibits production of carotenoids. Symptoms Bleaching on new growth Examples Isoxaflutole Comments No commercially available tolerant crops at this time. Estimated release is mid decade pending regulatory approval

12 Pigment Inhibitors HPPD Inhibitor Inhibits a key step in plastoquinone biosynthesis which indirectly inhibits production of carotenoids.

13 Photosynthesis Inhibitors Photosystem II Inhibitors Disrupts processes and products needed for transport of chemical energy. Causes cell membrane disintegration. Different binding than SOA groups 6 & 7. Symptoms Yellowing & necrosis Stunting Examples Metribuzin Comments Some soybeans are extremely sensitive to carry over Traditional trait testing of +/- not done, instead rated on a tolerance scale

14 Photosynthesis Inhibitors Photosystem II Inhibitors Disrupts processes and products needed for transport of chemical energy. Causes cell membrane disintegration. Different binding than SOA groups 6 & 7.

15 Cell Membrane Disrupters PPO Inhibitors Inhibits protoporphyrinogen oxidase, an enzyme involved in chlorophyll and heme synthesis. Causes a chain reaction that leads to cellular leakage and death. Symptoms Yellow & necrotic spots on leaf margins Examples Sulfentrazone Comments Some soybeans are extremely sensitive to carry over Traditional trait testing of +/- not done, instead rated on a tolerance scale

16 References & Acknowledgements Printed Materials United Soybean Board, (2014) Herbicide Classification Guide, Take Action, Herbicide-Resisitance Management. Philip L. Nixon and Mark Mohr, University of Illinois Extension. (2002) Illinois Pesticide Applicator Training Manual Demonstration and Research, Urbana, IL University of Illinois at Urbana-Champaign

17 References & Acknowledgements Websites Bayer CropScience. Balance GT. Retrieved from Dow AgroSciences. Enlist Weed Control Systems. Retrieved from Monsanto. Roundup Ready Xtend Crop System. Retrieved from s/roundup-ready-xtend-crop-system.aspx

18 References & Acknowledgements People Aaron Hager, University of Illinois Extension Specialist -Weed Science. Urbana, IL Photos Matt Raymond, Illinois Crop Improvement Association, Inc. Champaign, IL

19 The End Questions?