Straight Talk About Dicamba: Explaining 2017, Preparing for 2018

Thomas J. Peters

Extension Sugarbeet Agronomist and Weed Control Specialist

North Dakota State Univ. / Univ. of Minnesota

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© 2017 Regents of the University of Minnesota. All rights reserved.

STATE RESTRICTIONS - MN 24(C) EXPIRES ON 10/1/2018

• No application shall be made after June 20, 2018

• No application shall be made if the air temperature of the field at the time of

application is over 85 degrees Fahrenheit OR if the National Weather Service’s

forecasted high temperature for the nearest available location for the day exceeds

85 degrees Fahrenheit. ✓ Local National Weather Service forecasts are available at https://www.weather.gov/phi/localclimate

• Retail sale to and use ONLY by Certified Applicators

• Registrants are responsible for dicamba-specific training ✓ ~90 minute, in-person session that is free of charge

✓ Attendance records maintained by registrants

✓ One training session satisfies requirements for any of the three dicamba products

✓ MCPR will maintain training session calendar at:

✓ https://mcpr-cca.org/dicamba-information-trainings/

Dicamba Learning from 2017

• Inversions were not understood; occur more frequently than realized

• Handling and mixing; a small amount of contamination will cause damage to sensitive soybean

• Dicamba herbicide is weed control tool and not a weed control program

Please ask questions throughout!

Dicamba History

2017 in Review and Preparing for 2018

Weed Management

5 min 15 min 10 min

Q & A

5 min

Dicamba Herbicide

• Synthetic auxin herbicide in the benzoic acid chemical family

• Discovered in 1958 and first marketed in 1964 as Banvel DMA salt

• Clarity DGA salt marketed in 1992

• Sixth most widely used herbicide in the U.S., with more than 25 million acres of farmland treated annually

• Controls annual and perennial broadleaf weeds in grass crops

• Would offer a different mode of action for control of tough-to-control broadleaf weeds in soybean

Slide credit: Dr. Jim Griffin, Louisiana State University

Vapor Pressure of various compounds Pressure at which vapor phase is in equilibrium with its liquid/solid forms

Compound mmHg at 100F SI units Volatility

Glyphosate 0.00000002 10-8 Non-volatile

Dicamba salt 0.000002 10-6 Non-volatile

Dicamba acid 0.00002 at 75F 10-5 ?

Dicamba acid 0.004 at 100F 10-3 ?

Eptam 0.03 10-2 Volatile

Water 24 101 Volatile

Acetone 229 102 Volatile

Ammonia 7524 103 Volatile

Challenge: Can dicamba acid be formulated in salts that are non-volatile?

Challenge: Are dicamba salt formulations durable?

Engenia™ Herbicide Most Flexible and Advanced Dicamba for DT Crops

The Line:

Ionic Bond

The Boat:

Dicamba acid

The Anchor:

DGA Salt

The Anchor:

BAPMA Salt

BAPMA is a Bigger and Stronger “Anchor” for Dicamba

DGA Dicamba

Always read and follow label directions. Engenia is a US EPA Restricted Use Pesticide.

Volatility has been addressed with new low volatility formulations

and restrictions on tank mixtures and adjuvants

Mechanisms of Off-target Movement Thermogravimetric Analysis % Relative Volatility

Clarity®

herbicide

Banvel®

herbicide

>90% Reduction in Volatility

Compared to Clarity herbicide

Test conditions: Temp = 100° C/212° F, Time = 20 hours, Air flow = 60 mL/min, RH = 0%

Engenia®

herbicide

Always read and follow label directions. Engenia is a US EPA Restricted Use Pesticide.

Estimates of impacted acres, by state State Date Complaints Investigation Estimated acres

Minnesota August 25, 2017 225 52 150,000

North Dakota August 21, 2017 130 28 150,000

August 10, 2017

Slide Credit: Dr. Kevin Bradley, University of Missouri

October 15, 2017

Total: ~3.6 million

Dicamba Damage Complaints in Different Counties of MN

Total counties

reporting: 47

Total dicamba-related damage cases – 249 Misuse investigations assigned to Ag Chemical Investigator’s – 55 Normal year pesticide misuse investigations - ~100

Slide credit: Dr. Jeff Gunsolus, Univ of Minnesota

What happened in 2017?

• Cupping leaf phenotype appeared 14 to 21 days after application

• Areas with the most Xtend soybean and sprayed with Engenia, XtendiMax, or FeXapan are areas with the greatest amount of off-target movement and damage

• Air temperature and lack of precipitation in late June and July exasperated damage in Cass County, ND

• Was volatility related to air temperature?

• Was volatility related to lack of precipitation?

• How?

Dicamba impact on North Dakota and Minnesota agriculture

• Soybean acreage in 2017 o North Dakota, 7.2 million acres

o Minnesota, 8.2 million acres

• Time of application o Small grains and corn, May and early June

o Soybean, June and early July

• Dicamba rate: o 0.5 to 1 fl oz ai, wheat

o 2 to 4 fl oz ai, corn

o 8 fl oz ai, in dicamba tolerant soybean

• Technology adoption and market share growth

Observed soybean injury (non DT) from RR Xtend Soybean Technology Particle movement (including inversions)

Volatilization

Sprayer cleanout - contamination

Misapplication

Image Credit: BASF

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© 2017 Regents of the University of Minnesota. All rights reserved.

Source: Dr. Bob Hartzler, Iowa State University, “Not all Drift is Created Equal”

Lowest Observable Dose Causing

Significant Visual Crop Response

Soybean flat dose response to dicamba

Soybean show leaf cupping at a wide dose rate

Leaf cupping Stunting Chlorosis/necrosis Aborted flowers Distorted pods/seeds

2017 BASF field research trials

Dicamba “Flat” Response Curve 8-Fold difference in exposure

1/2000X

1/4000X 1/500X

1/1000X

Based on 0.5 lb ae/A as the 1X rate

Can be difficult to differentiate symptomology across rates

These slides were prepared by BASF to satisfy US EPA requirements. Please check with your state pesticide regulatory authority as additional requirements may be imposed by state regulatory authorities. DATE 11/17.

There are four routes by which dicamba can move from its intended target

• Physical drift at the time of application • Wind speeds are too great • Use of improper nozzles that produce fine droplets

• Tank contamination via improper spray tank cleanout • It takes very, very little dicamba in the tank to cause problems on non-Xtend soybean

that are sprayed after a dicamba application • Small quantities of dicamba in the transfer equipment

• Temperature inversions • Evening hours around sunset, persist for 8 to 10 hours • When the air nearest the earth's surface becomes cooler than the air above it

• Volatility • Dicamba is an inherently volatile herbicide • We know that the older dicamba formulations are less durable; lower molecular weight,

weaker ionic bond

Wind speed requirements Spray when winds are 3 to 10 MPH

Wind Speed Label Requirement Comments

< 3 mph DO NOT spray Avoid temperature inversions

3 to 10 mph Spray ONLY IF wind is blowing away from neighboring sensitive crops

This includes non-dicamba tolerant soybeans

> 10 mph DO NOT spray Consider wind gusts

Monitor and document wind speed and direction before and after application. Measure wind speed at boom height in field

How much dicamba per acre does it take to injury sensitive soybean?

Slide Credit: Stanley Culpepper, Univ of Georgia

Simple handling and mixing model Few points for possible contamination

Sprayer is the only source of contamination concern Image credits: BASF

Complex handling and mixing model Multiple points for possible contamination

In-field mixing and filing Product storage

Product mixing

Product transfer

Nurse truck ‘hot loads’

Anything formulated product or spray solution touches can be a source of contamination

Image credits: BASF

Temperature inversions, impact on off-target movement

• Small droplets can remain suspended in air and move great distances for as long as inversion lasts

• Symptomology over larger geographical area

• Direction and distance of movement is not predictable

DO NOT make applications when an inversion exists at the field level

Slide Credit: Daryl Ritchison

V1 – 11/2016

Some things a grower can control

Once the droplet leaves the nozzle then no control

What happens to bapma salt or Vapor Grip after droplet is released from nozzle? 1. Deposit formation after water evaporation

2. Affect of pools of H+ on leaf surface and soil

3. What is the effect dew and small rain events

Dicamba is water soluble

Herbicide H20 Solubility (ppm)

Prowl 0.33

Atrazine 35

Callisto 160

Harness/Surpass 282

Dual Magnum 530

Glyphosate 10,500

Dicamba 250,00

Paraquat 620,000

Absorption of dicamba in plants Adsorption of dicamba to soil

Soil adsorption coefficient • amount of chemical adsorbed to soil per amount of water

• Kd = concentration of chemical in soil/water

• Kd values vary greatly because OM is not considered in the equation

• Koc = (Kd * 100)/ % organic carbon

• Koc is also known as organic carbon-water partition co-efficient

pie adsorbed onto body

pie absorption into body

Kd or Koc measures the mobility of a substance in soil. A very high value means it is strongly adsorbed onto soil and organic matter and does not move in soil. A very low value means it is highly mobile in soil.

Dicamba physical properties

Common Name Trade Name Koc (mg/L) Kd (mg/L)

Acetamides Warrant 100 - 600 1.1 – 2.7

DNAs Treflan 3,000 – 9,000

EPTC Eptam 136 - 264 0.77 - 3

Sulfentrazone Spartan 43 1

Common Name Trade Name Koc (mg/L) Kd (mg/L)

Glyphosate Roundup PowerMax 24,000 324 – 600

2,4-D 2, 4-D 20 – 136 0.17 – 1.27

Clopyralid Stinger 60

Picloram Tordon 17 - 160 0.5

Common Name Trade Name Koc (mg/L) Kd (mg/L)

dicamba 2 0.05 – 0.13

Slide Credit: R Zollinger, NDSU

Temperature (C)

22 24 26 28 30 32 34 36 38

Dic

am

ba L

oss (

%)

0

2

4

6

8

Engenia

Engenia + AMS

BASF Lab Study

Engenia herbicide: 12.8 fl oz/A

AMS – 0.5% w/v at 10 GPA

Test Conditions:

Duration: 24 hours

Air flow: 0.5 l/min

using 2.5 l tank

RH: 35%

Substrate: glass

+ AMS

Impact of AMS on Dicamba Volatility

Engenia®

herbicide

Solo

AMS increases potential volatility by 20 times Always read and follow label directions. Engenia is a US EPA Restricted Use Pesticide.

These slides were prepared by BASF to satisfy US EPA requirements. Please check with your state pesticide regulatory authority as additional requirements may be imposed by state regulatory authorities. DATE 11/17.

72 75 79 82 86 90 93 97 100

Temperature (◦F)

Dicamba is a tool and not a program • Observed RR, LL, and Xtend soybean in 2017

• Observed clean and dirty fields with each technology

• Herbicide trait will not solve weed resistance

• A solid weed management plan can

Werle, Rodrigo. Lowell D. Sandell, Douglas D. Buhler, Robert G. Hartzler, and John L. Lindquist. Predicting Emergence of 23 Summer Annual Weed Species. 2014. Weed Sci. 62:267-279.

Weed emergence patterns

Kochia control in LibertyLink and Xtend Soybean, Barney, ND

Herbicide treatment1 Application

Herbicide rate (oz, fl oz or pt/A)

Jun 1

Jun 29

Sept 7

----------% control----------

Dual Magnum + Valor / Liberty

PRE /

POST

1.3 pt + 1 fl oz / 29 fl oz 0 49 27

Sharpen + Warrant /

Engenia + PowerMax

PRE /

POST

1 fl oz + 3 pt / 13 fl oz + 28 fl oz 0 81 68

Engenia / Engenia + Warrant /

PowerMax

PRE / EPOST /

POST

26 fl oz / 13 fl oz + 3 pt / 32 fl oz 100 94 97

Engenia + PowerMax/

Engenia + PowerMax

EPOST /

POST

13 fl oz + 28 fl oz/ 13 fl oz + 28 fl oz 100 96 100

LSD (0.05) 14 20 21

1Liberty applied with N-Pak ammonium sulfate at 3 lb/A, Engenia plus PowerMax with Class Act Ridion at 1% v/v, PowerMax with N-Pak ammonium sulfate at 1.5 lb/A and NIS at 0.25% v/v.

Lambsquarters control (early germinator) from preemergence and postemergence herbicides, near Moorhead, MN in 2017

Lambsquarters

Treatment1 Rate oz/A* or fl oz/A

Timing Jul 27 Aug 23

% %

PowerMax / PowerMax 28 / 28 EPOST / POST 98a 96a

Rowel + XtendiMax / XtendiMax +PM

2* + 22 / 22 + 32

PRE /

POST 96a 83a

Dual Magnum + Valor SX / Liberty

1.3 pt + 2* / 29

PRE /

POST 78b 58b

Liberty / Liberty 29 / 29 EPOST / POST 94a 73ab

Authority MTZ / Liberty 15* / 29 PRE/POST 98a 94a

1PowerMax + XtendiMax with Class Act Ridion at 2% v/v plus Intact at 0.5% v/v. PowerMax alone with Prefer 90 NIS at 0.25% v/v plus N-Pak AMS at 2.5% v/v. Liberty alone or in tank-mixes with N-Pak AMS at 5% v/v.

Waterhemp control (late germinator) from preemergence and postemergence herbicides, near Moorhead, MN in 2017

Waterhemp

Treatment1 Rate oz/A* or fl oz/A

Timing Jul 27 Aug 23

% %

PowerMax / PowerMax 28 / 28 EPOST / POST 13b 0c

Rowel + XtendiMax / XtendiMax +PM

2* + 22 / 22 + 32

PRE /

POST 88a 66b

Dual Magnum + Valor SX / Liberty

1.3 pt + 2* / 29

PRE /

POST 88a 79b

Liberty / Liberty 29 / 29 EPOST / POST 93a 70b

Authority MTZ / Liberty 15* / 29 PRE/POST 98a 98a

1PowerMax + XtendiMax with Class Act Ridion at 2% v/v plus Intact at 0.5% v/v. PowerMax alone with Prefer 90 NIS at 0.25% v/v plus N-Pak AMS at 2.5% v/v. Liberty alone or in tank-mixes with N-Pak AMS at 5% v/v.

Dicamba Recommendations for 2018 • What is my most important weeds?

o Do they emerge early or late?

• Target early postemergence application timing

o PRE? No! There are much better PRE heribicides

o Target early POST

Thank you for your Support

Tom Peters

• Extension Sugarbeet Agronomist and Weed Control Specialist

• thomas.j.peters@ndsu.edu BeetWeedControl @tompeters8131

• 701-231-8131 (office)

• 218-790-8131 (mobile)