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Bob HartzlerExtension Weed ScienceDepartment of Agronomy
A historical perspective on dicamba
Dicamba ag timeline
1950196019701980199020002010 2020
dicambadiscovery
Banvelapproved foruse
Banvel II*(Na+salt)
Marksman(dicamba +atrazine)
Clarity *
(DGAsalt)
Distinct(dicamba +diflufenzopyr)
Status(dicamba +
diflufenzopyr +safener)
Engenia *,Fexapan VGT *,Xtendimax VGT *
*Low-vol formulations
Labelexpansion
% of U.S. Corn Acres Treated
Source:PesticideUseinUSAgriculture.1960-2008.Fernando-Cornejoetal.ERS/USDA.May2014.
dicamba
0
10
20
30
40
50
1979 1985 1990 1995
US Iowa
Dicamba use in U.S. and Iowa corn
%cornacrestreated
USDA/ERSWintersteen andHartzler
0
10
20
30
40
50
1979 1985 1990 1995
HighpHsoilsinNWandNCIowalimiteduseofatrazineduetocarryover,thusdicamba (usuallyusedincombinationwith2,4-D)wasthemostpopularherbicideinthispartofIowa.
Dicamba use in U.S. and Iowa corn
%cornacrestreated
0
20
40
60
80
100
SEIANWIA%cornacrestreated
Dicamba useinIowa.1985.
USDA/ERS.Wintersteen andHartzler.
%cornacrestreated
• “. . . dicamba presents a much greater hazard to nearby soybeans than 2,4-D. For that reason, the use of dicamba in Illinois has been discouraged.”
Ellery Knake, UI, 1971
Concerns regarding off-targetmovement are not new
E.Knake.1971.Effectofdicambaonsoybeans.Agron.Facts.
• 31% of farmers used dicamba• 20% of corn treated with dicamba• Canada thistle primary target• Ten drift incidences (20% of farmers using dicamba)
– Six were ‘self-inflicted’ damage– Two cases involved more than 4 hectares– One case with suspected yield loss
1977 S. Dakota dicamba use survey
Auch andArnold.1978.WeedSci.Samplesize=160S.D.farmers
• Do not apply if wind >5 MPH towards sensitive crop• Do not apply if >85 F on day of application• Use coarse sprays and PSI < 20• Do not apply in vicinity of beans if:
– Corn is >24” tall, or– Soybeans > 10” tall, or– Soybeans have begun to bloom
1984 Illinois Banvel Recommendations
Anderson,Knake,andMcGlamery.1984.Effectofdicamba and2,4-Donsoybeans.AgronomyFacts.
0
20
40
60
15 20 25 30
Temperature
0 25 50 75
Sodium
Potassium
TEA
DMAFormulation(salt)
Dicamba volatility. 1979. Behrens and Leuschens. Weed Sci. 5:486-493.
%soybeaninjury
%so
ybeaninjury
Temperature (∘C)
d
d d
020406080
Exp1 Exp2 Exp3
%soybe
aninjury
Timecourseofvolatilization
0
15
30
45
SBleaf Cornleaf Soil
%soybe
aninjury
Applicationsurface
Day1
Day2 Day3
0 20 40 60 80
Notconcerned
Itismanageable
Somewhatconcerned
Extremelyconcerned
Levelofconcernregardingfutureuse
0 1 2 3 4 5 6
Particledrift
Inversion
Volatility
Applicatorerror
Contamination
Primarycauseofdicamba injurytonon-DRsoybean
IFCA Ag Retail Survey. Aug, 2017
IllinoisFertilizerandChemicalAssociationBloomington,IL.28Aug.,2017.Online.
• Dicamba has a long history of ‘safe’ use
• Risk of off-target injury has limited treated acres since dicamba’s introduction
• Early ’low-volatile’ formulations (e.g. Banvel II, Clarity) failed to eliminate problems with vapor drift
Summary
