2/1/2018. What s Happening in Our Fields? Off-Target Dicamba Movement

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1 What s Happening in Our Fields? Official Dicambarelated Injury Investigations as Reported by State Departments of Agriculture (*as of October 15, 2017) *Total: 2, Dr. Kevin Bradley, University of Missouri OffTarget Dicamba Movement Generally recognized as sources spray particle drift volatility and transport tank contamination Other possibilities soil and water movement transfer by equipment transfer by human or animal activity 1

2 North Dakota Dicamba Use Before wheat, corn, pasture add 25% soybean acreage 550,000 to 700,000 A 3,000,000 A (5x) geography concentration (23x) 1 to 2 oz ae/a 8 oz ae/a (4x) Potential Dicamba Presence previous exposure x 5 acreage x 2 adoption x 4 rate = Why did dicamba drift? Application timing of dicamba on crops EARLY timing on wheat or corn = 2 to 4leaf LATE timing on DT soybean = PRE through R1 June through midjuly Atmospheric Loading Early timing leaves greater potential for flushing rain Also cooler, to be discussed later Herbicide water solubility Herbicide H 2 O solubility ppm) Atrazine 35 Callisto 160 Harness/Surpass 282 Metolachlor 530 Prowl 0.33 Glyphosate 10,500 Dicamba 250,000 Paraquat 620,000 Dry summer Soybean injury to dicamba and 2,4D USDA Drought Map JulyAugust 2017 Robinson et. al Weed Sci 61: Robinson et. al Weed Sci 61:6876 Soybean is 100X more tolerant to 2,4D 2

3 Platitude: A word or phrase used too often to be meaningful Soybean susceptibility to dicamba Lowest rate response: Labeled rate % of rate Dicamba on soybean 0.5 lb ae/a 0.005% Glyphosate on corn 0.75 lb ae/a 1% Glyphosate on soybean 0.75 lb ae/a 10% Dicamba drift on sugarbeet and sunflower Soybean is 2,000X more susceptible to dicamba than glyphosate Lowest soybean rate response to dicamba: g/ha = no response (Egan and Mortensen 2012) g/ha (Robinson et al. 2013) 0.28 g/ha (Soloman and Bradley 2014 Dr Brian Jenks, NDSU Summary of dicamba yield studies 3.7 g/ha 3.2 g/ha Andrew Kniss, University of Wyoming <0.5 g/ha 1 g/ha = 0.2% of 0.5 lb/a Some things a grower can control. Once the droplet leaves the nozzle then no control V1 11/2016 What is the point of this data? What is the point of this data? 3

4 None/Low Wheat Barley Corn Canola Flax Crop susceptibility to dicamba NDSU Moderate Alfalfa Potato Safflower Sunflower Tomato Severe Chickpea Dry bean Field pea Lentil Sugarbeet Extreme/ Canary in the coal mine Soybean Very important question 1. What happens to bapma salt and Vapor Grip after droplet is released from nozzle? 1. Deposit formation after water evap. 2. Pool of H + on leaf surface and soil 3. Effect dew and small rain events *Classification is visually detectable injury; North Dakota crops Very important question As water evaporates in droplet: protons (H+) accumulate ph decreases = lower acidity acidity increase protonation (pka) protonated dicamba = dicamba acid dicamba acid = volatile form How does that affect the Vapor Grip? Questions: 1. How much dicamba is FREE? 2. What is the fate of dicamba? 3. In what form is free dicamba? Herbicide Absorption Dicamba Absorption Data How much glyphosate is absorbed? = ~33% How much dicamba is absorbed? Wheat = 80% (Cessna Weed Sci 41:682686) Leafy spurge = 60% (Lym et al. Weed Tech 19:329341) Kochia = 35% (Cranston et al. Weed Sci 49:164170) Apple leaf cuticles No adjuvant = 15% 6 adjuvants at 2 rates = 25 to 30% (Adams and Zollinger, 2016 absorption studies conducted in Germany in collaboration with Clariant) 4

5 Dicamba Absorption Data Soybean = () surfactant = 38% (+) surfactant = ~75% hardtowet Easytowet Dicamba Absorption Data Average absorption Soybean = 3875% Leafy spurge = 60% Kochia = 35% Apple cuticles 15% 30% ~50% absorbed ~50 unabsorbed! 0.25 lb of dicamba on leaf + soil surface In North Dakota 750,000 lbs of dicamba FREE! What does dicamba look like after water is gone? Herbicide deposit on leaf surface Dicamba crystallization on leaf surface Deposit of dicamba crystals after water evaporation from droplet. What is the fate of dicamba? Dissociated or acid? Wetting from dew? Wetting from light rain? Recrystallized? Glyphosate deposit 2,4D ester Scanning electron microscope Adams and Zollinger NDSU Universal principle of chemistry = ADSORPTION Soil particle Soil particles with () charges Dicamba Physical Properties Koc (mg/l) Kd (mg/l) Acetamides DNAs EPTC Sulfentrazone 43 1 Glyphosate 24, ,4D Clopyralid ~60 Fluroxypyr Picloram Dicamba?? 5

6 Temperature (F) 2/1/2018 Dicamba Physical Properties Koc (mg/l) Kd (mg/l) Acetamides DNAs EPTC Sulfentrazone 43 1 Glyphosate 24, ,4D Clopyralid ~60 Fluroxypyr Picloram Dicamba Not adsorbed! Herbicide vapor pressure mm Hg (mercury) Liberty (x10 12 ) Paraquat (x10 9 ) Glyphosate (x10 8 ) Treflan (x10 4 ) 2,4D salt Not volatile 1.4 x 10 7 ester (x10 4 ) acid 0.4 (insoluble in water) Dicamba salt (x10 6 ) acid (x10 5 ) at 75F acid (x10 3 ) at 100F Eptam 0.03 (x10 2 ) Water 24 Temperature and vapor pressure of dicamba Why Engenia Herbicide? A stepwise improvement on reduced volatility Bare ground soil temp Notill soil temp Relative Volatility vs. Form of Dicamba 1 XtendiMax with Vapor Grip = 90% lower volatility than Clarity 100F = (x10 3 ) 75F = (x10 5 ) Air temp Engenia = 70% lower volatility relative to Clarity 0 1 Volatility ratings using five different measurement techniques: Field testing, Humidome, TGA, C 14, Incubator Engenia Molecular Weight Theory What is wrong with this picture? Dissociation fundamental principle of chemistry + Dicambabapma or dga or dma Salt compounds dissociate in water! GlyphosateK, IPA 2,4Ddma BasagranNa FlexstarNa LibertyNH 4 RaptorNH 4 StatusNa Stingermea DicambaNa, dma, dga, bapma 6

7 Dissociation + Dicambaacid = Volatile +H + Dicamba Physical Properties pka = the ph value at which equal concentrations of the acid and conjugate base forms of a substance. At pka: 1/2 molecules lose their protons = anion 1/2 molecules retain protons = neutral Dicambabapma or dga or dma Dicambaanion = Not volatile Dicamba pka = 50% molecules = anion = No volatility 50% molecules = acid = High volaitility Dicamba Physical Properties pka Paraquat Glyphosate 2.6, 5.6, ,4D 2.73 Aminopyralid 2.56 dissociated and () charge Clopyralid 2.3 dissociated and () charge Fluroxypyr 3 Picloram 2.3 Dicamba 1.87 Low H+ High H+ Dicamba Physical Properties XtendiMax with Vapor Grip? H ph < 5.5 = dicambadga + dicambaacid ph > 5.5 = dicambadga dicambaanion Dicamba pka = ~2 dissociation constant ph 6 = : 0.01 ratio of anionic : acid molecules ph 5 = 99.9 : 0.1 ph 4 = 99:1 ph 3 = 90:10 ph 2 = 50:50 What is Vapor Grip? H + BAPMA: DGA: H 2N O OH Engenia Herbicide Why will AMS be restricted? + AMS Mechanism of action: 1. NH3 volatilizes 2. Leaves behind H+ 3. H+ lowers ph 4. > dicambaacid Polyethylenimine Mol. wt = ~2 m Anion scavenger DMA: Undissociated Engenia Dicambaanion Many other anions can compete with binding sites. Application rates: Engenia 560 g/ha AMS 0.5% w/v Test Conditions: Time: 1 day (24 hr), Air flow: 0.5 l/min using 2.5 l tank, Relative Humidity: 5%, Substrate: glass 7

8 Ammonia loss from soil, ND Neutral ph Conventional till Slightly acid ph Notill 2015, Franzen, NDSU Ammonia exchange from corn foliage during reproductive growth. Francis, Schepers, and Sims Agron J 89:94194(1997) Ammonia exchange from corn foliage during reproductive growth. Francis, Schepers, and Sims Agron J 89:94194(1997) Nitrogen in plant foliage can be lost by volatilization (Farquhar et al., 1980) Loss of NH3 was found to occur during all sampling periods Highest volatilization rates occurred during reproductive growth (Harper et al., 1987; HoltanHartwig and Bockman, 1994) Agricultural crops (i.e. corn) grown under high N fertility levels will loose high levels of NH3 (HoltanHartwig and Bockman, 1994) Large number of plant communities dispersed across the land suggests that, in aggregate, vegetation is a significant source for atmospheric NH3. Dicamba Summary: 1. Unprecedented soybean susceptibility 2. Atmospheric loading 3. Low foliar absorption 4. No soil adsorption 5. High air and soil temperatures 6. Dissociation of salt 7. Fate as salt or acid 8. Pools of ammonia from soil and plants The field study found that 15% of the applied N was lost as ammonia. 8

9 Yield Loss (%) 2/1/2018 Factors to reduce secondary dicamba drift: ND Weed Guide page PRE only and maybe EPOST 2. Temperatures below Sufficient rain to deposit dicamba in soil Dicamba Injury Resulted in Yield Loss Volatility Particle movement and volatility 70 Seed produced at 2030% plant injury Slight (010%) Moderate (2030%) Severe (4050%) Visible Soybean Injury Seed and Progeny of Damaged Soybean Slightly smaller seed No effect on oil, protein, or density Inconsistent trends toward lower germination toward less vigor Plant development in early stages was not affected Updated EPA requirements among others Soybean Dicamba pesticides are now restricted use products (RUPs) and can only be applied by certified applicators or those working under the direct supervision. The specialized record keeping requirements of the product. Applicator must first complete the required state Dicambaspecific training. New tank clean out instructions should be followed and DOCUMENTED. No applications can be made when the wind speed is more than 10 miles per hour. Absolutely no ammonium salts. Only approved tank mix partners can be used. All applications must be made with boom height 24 inches above the canopy or less. Do not apply near sensitive areas or crops. 9

10 ND Changes for 2018 Season No applications can be made after June 30 th These restrictions would only apply to postemergence applications of XtendiMax (Monsanto), Engenia (BASF), and FeXapan (DuPont) The vapor pressure of many pesticides including Dicamba increases as air temperature increases which makes them more prone to volatility. Higher temperatures are historically known to occur in late June and early July increasing the risk of volatility. The data we collected in 2017 shows that almost all damage reported came from applications that occurred in very late June through July. To address this concern the Department has placed a definitive cutoff date for applications. No applications may be made if air temperature of the field at the time of application is over 85 degrees Fahrenheit or if the forecasted National Weather Service high temperature at the nearest available location for the day exceeds 85 degrees Fahrenheit. North Dakota has a unique climate that is different than other soybean producing states. During the application season we typically have low humidity. The dry/less humid environment can significantly increase product evaporation and potential off target movement. June temperatures can often be unpredictable, and climb into the 80s and even 90s. Any high temperatures experienced during this time can greatly increase the chance of product volatility and potential off target movement. To safeguard against this, we have placed a temperature restriction on when applications can be made. Applications can only be made from one hour after sunrise to one hour before sunset Applicators must maintain a speed of 12mph or less while applying product Any applicator working under the supervision of a certified private applicator will also be required to complete Dicamba specific training before applying product 10

11 Applications must be made with a minimum of 15 gallons of spray solutions per acre No applications can be made using 80 degree or less spray nozzles Best Management Practices Consider utilizing preemergence weed management strategies Avoid relying solely on postemergence applications of Dicamba for weed control Remember for your spray records ND Law states: Restricted use applications and/or commercial applications need to be filled out within 24 hours of the application. Records need to be maintained for 3 years on all restricted use/commercial applications. 7 Reasons WHY dicamba drifted in 2017? Refer to page 29 in 2018 Weed Guide 11