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Optimizing Herbicide Performance

Optimizing Herbicide Performance. David Jordan North Carolina State University. Optimizing Herbicide Performance. Optimize the things you can control Minimize the risk of things you cannot control Know what you have and what works best on what you have

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Optimizing Herbicide Performance

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  1. Optimizing Herbicide Performance David Jordan North Carolina State University

  2. Optimizing Herbicide Performance • Optimize the things you can control • Minimize the risk of things you cannot control • Know what you have and what works best on what you have • Know whether you have resistant biotypes

  3. Preplant Burndown or Incorporated and Preemergence Performance • Must have water for activation • Must spread risk so that you get some activation of herbicides not incorporated • Overlapping PREs (2 wks ahead, at planting, with POST in season)

  4. Optimizing Herbicide PerformancePostemergence Herbicides • Weed size • Herbicide rate • Nozzle selection • Spray volume • Adjuvant selection • Water quality • Compatibility • Mixing interval

  5. Need to spray at this time! Might get lucky at this time

  6. Most POST soybean herbicide labels specify 6-leaf or 4-inch maximum Palmer amaranth Harmony SG label specifies 8-inch maximum Palmer amaranth We have to use comprehensive systems of PRE and POST herbicides. Roundup Ready, LibertyLink, and conventional systems have a place and all three can be very effective. BUT, it takes multiple applications of different modes of action in all three systems to get us where we need to be because of resistance!

  7. Spray Nozzles • Application technique is very important. • An excellent herbicide program can fail due to poor application. • Nozzle selection and proper operation are critical components of herbicide application.

  8. Nozzles

  9. Factors affecting nozzle flow rate: • Orifice size • Pressure • Specific gravity of spray solution • Viscosity of spray solution; primarily concerned • with drift control agents (no conversion factors) • Effect of increase in viscosity of spray solution • Nozzle flow rate Decrease • Spray angle of nozzle* Decrease • Droplet size** Increase • * example in next slide • ** principal behind drift control agents

  10. Results from Research in North Carolina with Drift Control Agents • Glyphosate • Glufosinate • 2,4-D • Dicamba

  11. Importance of Droplet Size • Droplet size affects coverage • Smaller droplets = better coverage • Droplet size not critical for PPI or PRE • Droplet size important for POST • Droplet size affects potential for spray drift • Smaller droplets = greater drift potential

  12. Spray Droplet Size • Expressed as VMD (volume median diameter) • VMD of 200 um means 50% of spray volume composed of droplets < 200 um and 50% of volume composed of droplets > 200 um

  13. Effect of droplet size on spray coverage

  14. Spray volume (GPA) equal in both cases.

  15. Importance of Droplet Size • Droplet size affects coverage • Smaller droplets = better coverage • Droplet size not critical for PPI or PRE • Droplet size important for POST • (reason POST herbicide labels often specify type of nozzle to use, or not to use)

  16. AI TeeJet air injection spray tips • Produce tapered flat fan pattern • Large, air-filled droplets • Promoted for drift management • Available only as110-degree angle • Designated as AI • Output rated as GPM at 40 PSI • Nomenclature: • AI 11002 VS

  17. Spraying Systems Greenleaf Technologies

  18. AI TeeJet air injection nozzles • Used for broadcast applications • Recommended pressure 30-115 PSI; pressure affects droplet size • Promoted for drift management; good for soil-applied and systemic POST • 4. Typically 20-inch boom mounting • 5. Recommend 30 to 50% overlap • 6. Suggested minimum height, • 20-inch spacing 15 to 18 inches

  19. Types (or functions) of Adjuvants* Surfactants Nitrogen fertilizers Spreaders Dispersing agents Stickers Compatibility agents Crop oils Foaming agents Wetting agents Foam suppressants Emulsifiers Buffering agents Penetrants Acidifiers Stabilizers Drift control agents Humectants Dyes, colorants Water conditioners UV absorbents * Some overlap

  20. Basic Types of Spray Adjuvants Activator adjuvants: enhance biological efficacy of the pesticide Utility/spray modifier adjuvants: modify physical characteristics of spray mixture

  21. Activator Adjuvants (enhance biological efficacy of the pesticide) Surfactants Crop oils Ammonium fertilizers

  22. Ionic Classes of Surfactants 1. Nonionic - no charge 2. Anionic - negatively charged 3. Cationic - positively charged 4. Amphoteric - positively or negatively charged, depending on pH Types 2, 3, 4 primarily are formulation adjuvants. Type 1 commonly used by growers.

  23. Organo-Silicone Surfactants • Tremendous capacity to reduce surface tension • Excellent droplet spreading • Sometimes called “super wetters” • Typically blended with non-ionic surfactants • Used at much lower rates than non-ionic surfactants • NIS 0.25% by volume • OSS 0.05% by volume • Expensive

  24. Crop Oil Adjuvants 1. Crop Oil a. Misnomer as the origin of the oil is not from plants. It is a derivative of paraffin-based petroleum oil. Also called phytobland oil. b. Consist of oil plus 1 to 2% surfactant to aid in mixing in water. c. Promote penetration of pesticide through waxy plant cuticle. d. Delay droplet drying time e. No longer used for herbicide applications

  25. Crop Oil Adjuvants 2. Esterified Seed Oils a. Produced by reacting fatty acids from seed oils with an alcohol to form esters. b. Methyl or ethyl esters then combined with a surfactant. Typically make methyl esters, and product referred to as methylated seed oil (MSO). c. MSO often boosts herbicide activity more than a COC or POC. d. Not commonly used in NC, but labels of certain products specify an MSO. Osprey and Option are examples of herbicides requiring MSO.

  26. Ammonium Fertilizer as an Adjuvant • Most commonly used are ammonium sulfate (AMS) • and urea-ammonium nitrate (UAN). • Less commonly used is ammonium polyphosphate • (10-34-0). • Ammonium ion thought to be largely responsible for • beneficial effect on herbicide performance.

  27. Ammonium Fertilizer as an Adjuvant • AMS typically recommended at 2.5 to 4 lb/A or • 8.5 to 17 lb/100 gal spray solution. • UAN typically recommended at 2 to 4 qt/A. • Labels which recommend use of an ammonium • fertilizer usually specify the fertilizer in addition to • NIS or COC. Fertilizer does not replace other • adjuvants • Several products on market that contain AMS • + surfactant + drift control agent.

  28. Alleviation of Hard Water Antagonism of • Glyphosate with Ammonium Fertilizer • “Hard” water contains cations such as Ca+2 • and Mg+2. Reduces efficacy of glyphosate. • These cations compete with isopropylamine • in formulated glyphosate isopropylamine • salt for association with glyphosate anion. • Resulting salt, such Ca-glyphosate, is not • absorbed well.

  29. Alleviation of Hard Water Antagonism of Glyphosate with Ammonium Fertilizer • “Hard” water contains cations such as Ca+2 and • Mg+2. Reduces efficacy of glyphosate. • These cations compete with isopropylamine in • formulated glyphosate isopropylamine salt for • salt for association with glyphosate anion. • Resulting salt, such Ca-glyphosate, is not • absorbed well. • Ammonium ion, if added to tank and agitated before adding glyphosate, may precipitate Ca and Mg ions, ultimately increasing weed control.

  30. Primary Utility/Spray Modifier Adjuvants 2. Defoaming agent: Definition* a material that eliminates or suppresses foam in the spray tank Commonly called defoamers *American Society for Testing and Materials

  31. pH of Spray Solutions • Can affect degradation rate in solution • Can affect solubility and polarity of • ionizable herbicides (more polar, or • less lipophillic, when ionized)

  32. Alkaline hydrolysis • Some insecticides degrade rapidly in high pH water; can even degrade in spray tank • Generally not a problem with herbicides; we basically do not worry about water pH when spraying herbicides • pH can affect water solubility of some herbicides, which potentially could affect absorption

  33. Adjuvant Selection Can Be Very Confusing!

  34. Adjuvant Selection Can Be Very Confusing • Hundreds of products available • Multiple-component adjuvants • No governmental regulation • Very limited unbiased testing • High profit item for distributors • Herbicide manufacturers reluctant • to recommend specific brands • Exaggerated claims, testimonials, • high pressure sales

  35. Selecting an Adjuvant 1. Read herbicide label. A. If label specifically says to not use adjuvant, then don’t use one. B. If label does not mention using adjuvant, follow personal experience, or seek advice of herbicide sales rep or extension. C. If specific brand of adjuvant recommended on herbicide label, use it if possible. D. If herbicide label recommends only a type of adjuvant, use recognized name brand from reputable distributor. Compare on basis of % active ingredient and cost.

  36. Selecting an Adjuvant 1. Read herbicide label. 2. Consider previous weather conditions, crop status, weed species, and weed size. 3. Go slowly with the “premium” adjuvants. Costly, probably no more efficacious than standard adjuvant. Conduct your own trials. Consider a water analysis. 4. Watch out for the snake oil man. If claims sound too good to be true, there is high probability they are not true.

  37. Time in Tank • Glyphosate and water quality • Compatibility

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