Adjuvants/Surfactants: Why We Use Them, How They Work, What Products Can Be Used Near/In Water? Tim Miller WSU NWREC

Transcription

1 Adjuvants/Surfactants: Why We Use Them, How They Work, What Products Can Be Used Near/In Water? Tim Miller WSU NWREC

2 What Is An Adjuvant? Any spray additive used with a pesticide that enhances the performance or handling of that pesticide There are many types of adjuvants (or spray additives), all providing different effects on the spray solution Over the next few slides, we ll discuss different adjuvants and their purpose

3 Major Examples of Adjuvants Surfactants Crop Oils Fertilizers and Water Conditioners Drift Control Agents

4 Surfactants Surfactants are products that enhance the ability of a herbicide to enter into a leaf or to stay in an aqueous solution Surface Active Agents All act on the surface tension of water Normally used at 0.25 to 1%, v/v (2 to 8 pt/100 gal) Most are nonionic surfactants (NIS), although silicon surfactants are also available

5 Major Types of Surfactants Emulsifiers Assist in forming emulsions (oil in water) Primarily used by manufacturers to formulate their oil-soluble products in water If products are water soluble, no emulsification is necessary Stickers Assist in spray retention on leaves Keeps the spray droplet from bouncing or rolling off Wetting Agents/Penetrants Assist in herbicide entry into the plant Gets the spray droplet to flatten out

6 Crop or Petroleum Oils Oils are products that enhance the ability of a herbicide to enter into a leaf Normally used at 0.25 to 1%, v/v (2 to 8 pt/100 gal) Most common oil additives for herbicides are Crop Oil Concentrates (COC) and Methylated Seed Oils (MSO) Dormant spray or superior oils are often used for insect or disease management in fruit production

7 Fertilizers and Water Conditioners Fertilizers and water conditioners can decrease antagonism of herbicides in hard water and enhance the ability of a herbicide to be translocated within a plant Ammonium Sulfate (AMS) or Ammonium Nitrate (AN) Normally used at 2%, wt/v (17 lbs/100 gals) Urea + Ammonium Nitrate (URAN) Liquid formulations containing 28 or 32% N Used at up to 4% v/v (4 gal/100 gal)

8 So How Do Surfactants Work?

9 So How Do Surfactants Work? Oil A simple situation: oil and water Water don t mix

10 Fats are nonpolar H H C=C=C=C=C=C=C=C or H H Oil H H H H H H H H H-C-C-C-C-C-C-C-C-H H H H H H H H H Water Water is dipolar + H + H O - l l l + H + H O - l l l + H + H O -

11 Surface Tension of Water Caused by hydrogen bonding between water molecules

12 Surfactants Are Two Compounds In One A Stylized Surfactant Molecule Polar end Nonpolar end Hydrophilic Head (water loving, oil hating) Hydrophobic Tail (water hating, oil loving)

13 Hydrophobic tails are happy in oil (both are nonpolar) Oil Water Hydrophilic heads are happy in water (both are polar)

14 Tails are not happy in air Air Water Heads are happy in water

15 Heads are not happy in air Air Oil Tails are happy in oil

16 Herbicide Water So, is this a good situation? (oily herbicide in a film on the surface of a water carrier)

17 Oil/herbicide droplet Heads are happy in water This is a Micelle Water carrier Tails are happy in oil

18 Lots of very small micelles in a bucket of water (or a spray tank) form an emulsion a common form for herbicide formulations The micelles help keep oil-soluble herbicides in solution with water, instead of separating in a film across the top

19 How Do Surfactants and Oils Improve Herbicide Uptake? The leaf surface restricts water loss and hinders uptake of liquids from the environment Hairs (density, length) Cuticle (wax, cutin, pectin) Stomata (holes in the surface that regulate gas exchange with the atmosphere)

20 Hairs on leaf

21 Leaves on hair Hairs on leaf

22 Hair leaves head Ho-o-gan!!

23 Leaf Cuticle

24 Cuticle Surface And Stomata

25 How Do Surfactants and Oils Improve Herbicide Uptake? Surfactants and oils: Cause greater droplet contact with the leaf surface and aid in movement into stomata Slow evaporation of herbicide droplets May increase rain-fastness of herbicides Assist in passage of hydrophilic herbicides through hydrophobic wax layers

26 Surface tension coupled with hydrophobic wax layer causes water to form droplets on leaf surfaces Cuticular Wax

27 Surfactants break the surface tension of water and make the water droplets spread out

28 Water droplet with no surfactant Water droplet with added surfactant

29 Adding surfactant to the mix can increase herbicide droplet contact with foliage Without surfactant With added surfactant

30 Mixing With Fertilizers Adjuvant activity from adding fertilizers like AMS, URAN, or AN to the spray mix relates to two (three?) phenomena Overcoming or tempering water hardness Assisting in herbicide translocation Slowing herbicide metabolism (?)

31 Herbicides Formulated As Salts Look for the terms dimethylamine salt or sodium salt or isopropylamine salt on the label These herbicides are antagonized by other salts in the water such as calcium, sodium, magnesium, and iron These elements form cations (positively charged ions) that react with negatively charged herbicide salts (like glyphosate) Both ammonium (H 1+ ) and sulfate (SO 4 2- ) are active Glyphosate is more readily absorbed when combined with ammonium than when combined with Ca 2+, Na 1+, Mg 2+, or Fe 2+ ions Free sulfate binds with Ca 2+, Na 1+, Mg 2+, or Fe 2+ ions

32 Physiological Effects of Herbicide /Fertilizer Mixes Adding AMS can increase movement of herbicide through the leaf cuticle, cell wall, or across the plasma membrane of the cells of certain weed species Studies show that basipetal movement of 14 C- glyphosate is increased when AMS is added due to improved cellular uptake and phloem mobility More glyphosate in plant cells could establish a concentration gradient increasing phloem loading and translocation

33 Things To Watch Out For The threshold level for hard water antagonism ranges from 150 ppm for calcium to 300 ppm for sodium Compatability problems from addition of liquid fertilizers If dry AMS is used, be sure to filter out non-soluble materials to prevent clogging of nozzles

34 Surfactants Approved For Aquatic Herbicide Applications In WA Agri-Dex Bond Bronc Max Bronc Plus Dry-EDT Class Act NG Competitor Cut-Rate Cygnet Plus Dyne-Amic Exciter Fast Break Fraction Intensify Interlock Kinetic Level 7 LI-700 Liberate Magnify One-Ap XL Pro AMS Plus Activator Penetrant Sinker Spray-Rite Tactic Tronic

35 What About Surfactant Toxicity? Studies have shown that cationic surfactants are more toxic than anionic surfactants and that nonionic surfactants are the least toxic Acute dosages of surfactant can damage the mucous covering of gills, and may cause fish injury or death depending on the degree of removal Metabolism of water may play a role in toxicity Aquatic invertebrates and shellfish are usually less sensitive to surfactants than are fish Frog larvae may be most sensitive to surfactant Crop oils and silicon surfactants also vary in toxicity to aquatic organisms

36 Surfactant Toxicity to Fish LC 50 for nonionic surfactants (such as X-77 and R-11) range from 4 to 12 ppm for fish, and from 1 to 16 ppm for aquatic invertebrates LI-700 has an LC 50 from 130 to 210 ppm for both types of organisms Worst case scenario (aquatic application in water 1 foot deep at maximum application rate) results in 0.2 to 0.3 ppm of surfactant Under these conditions, surfactant is practically nontoxic to rainbow trout

37 Surfactant Toxicity to Fish Newly-hatched rainbow trout fry were rather tolerant to nonionic surfactant, but become more sensitive as the yolk sac was absorbed (minimum LC 50 of 2.5 ppm at 23 days after hatching) After feeding for the first time, resistance increased and was maintained for at least 500 days (lifetime?) Sublethal effects for fish at 0.5 ppm Altered swimming and feeding behavior Affected fish did not recover even after 6 weeks in clean water Many (most) effects not well documented

38 How to Minimize Herbicide Use Near Water Early detection of weeds is essential Start with a positive identification Learn the weed species that you currently have, and where they are Be vigilant! Remove pioneer perennial and biennial weeds before they establish

39 Read and Follow the Label Herbicide rate Carrier volume Non-target species sensitivity Weed species susceptibility Tank mixtures Water use restrictions

40 Optimize Herbicide Applications Proper stage of growth Established perennial weeds Bud stage Late fall Biennial weeds During the first year of growth Annuals and seedling weeds As early as possible after seed germination is complete for the year

41 Optimize Herbicide Applications Temperature Moisture Leaf surface of weeds Dust Hairs Cuticle thickness and waxiness Surfactants

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