AGR 3102 (1) Principles of Weed Science Herbicide Muhammad Saiful Ahmad Hamdani

Week 8 – Topics Covered Herbicides: Classification cont… Formulation

Herbicides Classification… Selectivity: selective vs. non-selective  Activity: contact vs. systemic  Residual activity: residual vs. non residual  Time/type of application: pre-plant, pre- emergence, post-emergence  Placement: soil, foliar/plant  Methods of application: banding, broadcast, directed, spot treatment, wiping 

Herbicides Classification cont… G.Mode-of-Action Common method of grouping herbicides: mode-of-action (MOA). Classification based on similarity/dissimilarity of the herbicides chemistry and action. Each MOA has a designated numerical system (WSSA) and alphabetical system (HRAC).

What is MOA????? The first plant enzyme or site-of-action targeted/inhibited by the herbicide. Each herbicide group specifically inhibits specific functions, processes and systems in the cells. Different MOA group exhibits different injury symptoms.

Commercial Products ( Roundup ) Mode of Action (EPSPS Inhibitors) Site of Action ( EPSPS-shikimate pathway ) Chemical Family ( Glycines ) Active Ingredient ( Glyphosate )

2 types of herbicides: 1.Inorganic compounds - “old school” -Copper sulphate, ammonium sulphate, ammonium sulphamate, ammonium nitrate & ammonium thiocyanate -MOA: as desiccant/desiccating agent -High enviromentally persistent in soil & highly toxic to other organisms -Widely used in 1900s for aquatic and woody terrestrial plants, but no longer applicable. WHY?????

2.Organic compounds extensively synthesized following 2,4-D & other PGR commercialization. widely used in agric and non-agric areas. differ from one to another by their MOA. In general, divided into several important MOA groups:

Classification by Mode of Action 1)Synthetic Auxins & Auxin Transport Inhibitors 2)Amino Acid Biosysthesis Inhibitors 3)Fatty Acids Biosynthesis Inhibitors 4)Seedling Growth Inhibitors 5)Photosynthesis Inhibitors 6)Cell Membrane Disrupters 7)Pigment Inhibitors 8)Nitrogen Metabolism Disrupter 9)Unknown mode-of-action

1. Synthetic Auxins & Auxin Transport Inhibitors First commercialized in the 1940s to primarily control dicot weeds in many cereal crops. Broadleaf selective, systemic, post-emergence. Can affect monocots at high rates. Absorbed via foliar and roots. Short soil residual; average days. Synthetic auxin herbicides.

MOA = cause an auxin overdose. Auxin or indol-3-yl-acetic acid (IAA) = endogenous PGR crucial in cell division, differentiation, & elongation. Induces ethylene and ABA (plant maturity and senescence). Overdose = rapid & uncontrolled cell development & sudden plant maturing. Auxin transport inhibitors = unbalance auxin = unbalance cell development = unbalance growth.

2. Amino Acids Biosynthesis (ALS and EPSPS enzymes) Inhibitors 2 major MOAs: Acetolactate synthase (ALS) inhibitors and 5-Enolpyruvylshikimate 3-phosphate synthase (EPSPS) inhibitors. ALS synthesize 3 amino acids (leucine, isoleucine, valine); EPSPS (acids phenylalanine, tyrosine and tryptophan) = building block for protein. Protein needed for production of new cells & metabolic activity. Both systemic. ALS pre- and post-emergence, EPSPS post. ALS and EPSPS inhibitors non-selective.

Inhibition of ALS & EPSPS = shutdown of metabolic activity & no cell produced. ALS herbicides and glyphosate considered among the safest herbicides because ALS & shikimate-pathway exist only in photosynthetic plants & microorganisms and not in humans & animals. Soil residual: varies among ALS herbicides, generally about 2 weeks – 3 years (long persistence). EPSPS- little-no soil activity, residue days.

3. Fatty Acids Biosynthesis (ACCase enzyme) Inhibitors Selective-commonly referred to as graminicides (grass killers). Post-emergence, systemic. Inhibit fatty acid synthesis in plant plastid. Fatty acids important for development of meristem tissues. Some are sold as esters (ethyl or methyl, buthyl) to increase absorption. Grass ACCase in plastid highly sensitive to ACCase herbicides, others not

FOPs DIMs DEN

4a. Seedling Growth Inhibitors (Root & Shoot) 2 MOAs: microtubule inhibitors and cell wall (cellulose) biosynthesis inhibitors. Inhibit root and shoot development by interfering with cell division in meristematic areas. Effective only on germinating, small-seeded annual grasses and some broadleaves (seedling selective, systemic, pre-emergence).

Some need incorporation into the soil (esp. dinitroanilines) - subject to photo- degradation Have relatively long residual activity (more than a year).

4b. Seedling Growth Inhibitors (Shoot) 2 MOAs: lipid synthesis inhibitors & cell division inhibitors (VLCFA synthesis). Applied as pre-emergence/planting. Cause abnormal cell development or prevent cell division in germinating seedlings. Seedling-selective & systemic. Most effective on annual grasses and sedges, some can control small-seeded annual broadleaves.

Lipid synthesis inhibitors need soil incorporation, absorbed by emerging shoots. Cell division inhibitors absorbed by emerging shoots and roots. No control of established weeds.

5. Photosynthesis (at PS II) Inhibitors 2 types: soil applied herbicides (pre-& post- emergence); and foliar applied herbicides (post-emergence). Both systemic. Broadleaf selective. MOA: block the photosynthesis process = no food produced.

6. Cell Membrane Disrupters 2 MOAs: Protoporphyrinogen oxidase (PPO) inhibitors and PS I inhibitors. Both post-emergence and non-systemic (contact herbicides). PPO inhibitors and PS I inhibitors provide broad- spectrum control of many different species. PS I herbicide Paraquat: extremely toxic, no antidote so far ml fatal to human.

They burn plant tissues or desiccation. Symptom within an hour esp for Paraquat. Phytotoxicity increased by sunlight. PS I inhibitors have no phytotoxicity in soil (no root uptake).

7. Pigment Inhibitors (Bleaching Agents) 2 MOAs: Carotenoids synthesis inhibitors & HPPD (4- hydroxyphenyl-pyruvate-dioxygenase) inhibitors. Provide control of many annual broadleaves and some grasses (non-selective, systemic, some pre-, some post- emergence, some both). Carotenoids synthesis inhibitors inhibit carotenoids (chlorophyll protector) biosynthesis.

HPPD inhibitors interfere with normal chlorophyll activity. Carotenoid or chlorophyll inhibited: sun radiation damages chlorophyll pigments and the plant becomes “bleached” and dies. Referred to as “bleachers”.

8. Nitrogen Metabolism Disrupter Glufosinate-ammonium. Non-selective. Group H (HRAC) & 10 (WSSA). MOA = disrupting nitrogen metabolism, important for amino acids synthesis. Have both contact (major) and systemic (minor) actions on plants. Phytotoxicity increased by sunlight. Little to no soil activity (rapidly degraded by microorganisms).

9. Unknown MOA Herbicides Unknown MOA. Basically contact but some have limited translocation. Non-selective, post-emergence. Some have no soil activity and tightly bound to soil, some unknown. Some used as soil fumigants. Kill everything in the soil.

Why Understand Herbicide Mode of Action? Better understanding of how herbicides perform Improve herbicides performance Diagnosing herbicide injury Prevent and manage herbicide resistance

Herbicides Formulation Active ingredient (a.i.) = chemical that causes phytotoxicity & controls the target weed = the herbicide. Rarely for herbicide products to be made up only of a.i. Often diluted in other chemicals. Other chemicals: additives, diluents, extenders or adjuvant (no herbicidal activity) = inert ingredients.

Purpose: make the product easier to mix & apply, increase its efficacy, improve formulation stability & improve shelf-life/longevity. Mixture of a.i. and inert ingredients = formulation. Herbicides are sold in various formulations, depending upon: (1) the solubility of the active ingredient in water (2) the manner in which the product is applied (i.e. dispersed in water or applied in the dry form). 2 TYPES OF HERBICIDE FORMULATION:

A) Dry Formulations 1.Granules (G) A dry formulation (a.i., coated or adhered to some type of inert granule). Applied just as they are purchased with no mixing. Special granular spreader is required.

2.Pellets (P) A dry formulation - similar to granules only much larger. Pellets are applied directly to the target area by hand or with special spreaders.

3.Wettable Powder (W or WP) A dry powder (a.i., a diluent, and surfactants), water soluble. Spray tank agitation is necessary to avoid settling. 4.Soluble Powder (SP) A dry formulation that contains a high percent (>50%) a.i, water soluble. Need initial agitation to dissolve. No after-dissolve agitation is needed.

5.Water-Dispersible Granules (WDG) & Dry Flowable (DF) A dry formulation, water soluble. Easier to handle and measure than wettable powders. Spray tank agitation is necessary to avoid settling.

B) Liquid Formulations 1.Water Soluble Concentrate/Solution (WSC/S) A liquid formulation (a.i., water, sometimes a surfactant), water soluble/carrier. Have an amine (ammonium salt) or mineral salt in the molecule that enables water solubility. Agitation is not necessary.

2.Emulsifiable concentrate (E or EC) A concentrated liquid (a.i., petroleum solvents, emulsifier), oil and water based/soluble. Emulsifier - allows the formulation to be mixed with water to form an emulsion. Upon mixing with water, they take on a "milky" appearance. Mild agitation is sufficient.

3.Oil Soluble (OS) A liquid formulation (a.i. dissolved in oil or some other organic solvent. Must be applied in an oil-based carrier such as diesel fuel or kerosene. Mild agitation is sufficient.

4.Liquid/Flowable (F or L) A thick slurry-like liquid (a.i., water, and stabilizers), water soluble. Spray tank agitation is necessary to avoid settling.

5.Ready-to-Use Low Concentration Solutions (RTU). Ready to use and require no further dilution before application. Consist of a small amount of active ingredient (often 1% or less per unit volume) dissolved in an organic solvent.

1.Dry formulations: Spreader (Rotary, Drop) 2.Liquid formulations Sprayer (Handheld, Knapsack, Boom)

Drop

Sprayers

Some Things to Remember…. Photosynthesis = food Pigments (energy/light capture) = food Amino acids = proteins metabolism (growth) Cell membranes (lipids) = cell shape & rigidity Cell division = growth Hormone = growth and development Fatty acids = meristematic tissues development Nitrogen metabolism = amino acids synthesis

Some Things to Remember…. Herbicide formulations = herbicide mixtures and forms. Different formulation needs different carrier and applied differently.