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Soybean

Effect of Lactofen Application Timing on Yield and Isoflavone Concentration in Soybean Seed

^a Div. of Plant Sciences, Univ. of Missouri, Novelty, MO 63460
^b Veterinary Medicine Diagnostic Lab., Univ. of Missouri, Columbia, MO 65211
^c Dep. of Nursing, Truman State Univ., Kirksville, MO 63501

^* Corresponding author (nelsonke{at}missouri.edu)

Received for publication March 3, 2006. Postemergence application of the herbicide lactofen is known to increase phenolic compounds such as isoflavones in soybean [Glycine max (L.) Merr.] plants. We hypothesized that lactofen increases isoflavone levels in seed when applied at the R1 and R5 stages of development. Field research evaluated the effect of lactofen application timing and cultivar (‘Garst 3712’, glyphosate-resistant; ‘Big Bubba’, high-protein; and ‘Envy’, edamame) on crop response and seed isoflavone concentration. Lactofen at 70 g a.i. ha^–1 injured soybean 7 to 15% when compared with the untreated control 7 d after treatment. Lactofen applied to Big Bubba at the R5 stage of development increased concentration of genistein 78 µg g^–1 (11%), daidzein 82 µg g^–1 (9%), and total isoflavones 169 µg g^–1 (10%) compared with the nontreated control. Lactofen applied to Garst 3712 at the R5 stage of development increased daidzein concentration 52 µg g^–1 (7%). There was no effect of lactofen on isoflavone concentration in Envy seed. Seed yield averaged across the three cultivars was reduced by 290 kg ha^–1 when lactofen was applied at the R1 stage in 2002 and by 330 kg ha^–1 when lactofen was applied at the R5 stage in 2004. Results suggest a late application of lactofen may increase isoflavone concentration in seed of high-protein soybean cultivars, but this effect may be accompanied by a reduction in seed yield.