Vol. 54—2000 - NorthEastern Weed Science Society

EFFECTS OF MANGANESE AND BORON ON GLYPHOSATE AND SULFOSATE
ACTIVITY IN GLYPHOSATE- TOLERANT SOYBEAN
W.A. Bailey, H.P. Wilson, T.E. Hines, D.H. Poston and R.J. Richardson l
ABSTRACT
Foliarapplicationsof manganese(Mn) to soybean(Glycine max (1.) Merr.) area common
practicein coastalplainsoils wheredeficienciesof thisnutrientfrequentlyoccur. Thesefoliar
applications are typically made just prior to or at the bloom stage of soybean growth. Many
soybeanproducersapplyfoliarnutrientsandherbicidessimultaneouslyforconvenience.
However,somenutrientssuchas Mn affectherbicideperformancewhenmixedwithherbicides.
Recentspeculationthatfoliarapplicationsof boron (B) could enhancesoybean yield has
promptedinterestin mixingB withpostemergenceherbicides.
FieldexperimentswereconductedattheEasternShoreAgriculturalResearchandExtension
Center near Painter, VA in 1998 and 1999 to determine if additions of two formulations ofMn
and one of B would affect weed control by glyphosate and sulfosate. Glyphosate and sulfosate
rates were 0.5 and 1.0 Ib ailA in both yr and herbicides were also included at 1.25 lblA with Mn
in 1999. LigninandchelateformulationsofMn at4%v/v of the totalspraymix were included
both yr with each rate of glyphosate and sulfosate. All treatments with Mn were applied
approximately 30 d after planting. In additional treatments, the effects ofB at 0.251b1A with or
without 4.25 IbiA anunonium sulfate (NH.SO.) were investigated. Herbicides plus B
combinationswereappliedatsoybeanbloomorsequentiallyat 3 wk afterplantingfollowedby
applicationatbloom.
Soybean injury from herbicide treatments was genera11y 0 to 3% from glyphosate treatments
and 2 to 6% from sulfosate treatments regardless ofMn or B additions. Both Mn formulations
reducedcontrolof commonlambsquarters (Chenopodium album L.), commonragweed
(Ambrosia artemisiifolia L.), threemominggloryspecies(Ipomoea spp.), andlargecrabgrass
(Digitaria sanguinolis L.) by O.5lb/A glyphosate or sulfosate 28 to 53%. Similar reductions in
controlof commonlambsquarters, commonragweed,andlargecrabgrassoccurredwhenMn
lignin or Mn chelate were added to glyphosate and sulfosate at 1.0 and 1.25 IblA. Additions of
B or B plus anunonium sulfate to glyphosate and sulfosate did not reduce weed control in 1999.
In addition to other data, pHs of herbicide solutions were measured. Glyphosate and sulfosate
decreased pHs of water used as herbicide carrier from 7.8 to 5.1 and 4.9, respectively. Addition
of Mn lignin had little effect on raising the pH of standard herbicide solutions while additions of
Mn chelate and B (with or without anunonium sulfate) increased pH to 6.7 and 7.3, respectively,
in solutionswithglyphosateandsulfosate.
IGraduate ResearchAssistant,Professor,ResearchSpecialistSenior,FacultyResearch
Associate, and Graduate Research Assistant, respectively, Virginia Polytechnic Institute and
State University, Eastem Shore Agricultural Research and Extension Center, Painter, VA
23420-2827.
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