Lactofen Application Timing Affects Yield and Isoflavone Concentration in Soybean Seed

Isoflavones have been implicated in many health-related effects. A postemergence application of the herbicide lactofen (Cobra) has increased phenolic compounds such as isoflavones in soybean plants. We hypothesized that lactofen increases isoflavone levels in seed when treated at the early 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 concentrations. Application dates, and environmental conditions at the time of application were recorded in Table 1.

Injury from lactofen at 6 oz/acre plus NIS at 0.25% v/v plus 28% urea ammonium nitrate at 1 qt/acre was 10 to 14% seven d after the R1 application timing, and injury was 7 to 15% seven d after the R5 application timing (Table 2). Envy, an edamame type cultivar, is commonly consumed as fresh or frozen and harvested at the R6 stage of development. Lactofen applied during flowering (R1) reduced the number of pods with two seeds by 243,000/acre, total pods by 312,000/acre, and total pod yield by 980 lb/acre when compared to the non-treated control (Table 3). Lactofen applied during early seed development (R5) increased yield of pods with one seed 53,000/acre, but had no effect on total pod yield or pods with two or three seeds. None of the treatments affected brix levels in the seed of Envy.

Cultivar ranking for genistein and daidzein concentration was Big Bubba > Garst 3712 > Envy, while ranking for glycitein concentration was Garst 3712 > Big Bubba > Envy for non-treated seed samples (Table 4). Lactofen applied to Big Bubba in the R5 stage of development increased concentration of genistein 78 µg g^-1, daidzein 82 µg g^-1, and total isoflavones 169 µg g^-1 compared to the non-treated control. Lactofen applied at the R5 stage of development increased Garst 3712 daidzein concentration 52 µg g^-1. However, there was no effect of lactofen on isoflavone concentration in Envy seed. Seed yields were reduced 4 to 5 bu/acre when lactofen was applied at the R1 and R5 stages of development, respectively (Table 5).

Lactofen did not affect seed isoflavone concentration when applied at the R1 stage of development or when applied to Envy or Garst 3712 at the R5 development stage, but total isoflavone concentration increased 10% in Big Bubba when lactofen was applied at the R5 stage of development. Treatments that increase isoflavone concentration may hold potential for farmers seeking value-added opportunities and consumers seeking health promotion and disease prevention benefits of soy products.

Table 1. Lactofen application date, temperature, relative humidity, and soybean height at the time of application in 2002 and 2004.

^†R1 = beginning bloom, and R5 = beginning seed as outlined in Fehr and Caviness (1985).

Table 2. Soybean plant injury (0 = no visual crop injury and 100 = complete plant death) 7 d after application of lactofen at 6 oz/acre plus NIS at 0.25% v/v plus 28% urea ammonium nitrate at 1 qt/acre in 2002 and 2004.

^†R1 = beginning bloom, R5 = beginning seed as outlined in Fehr and Caviness (1985).
^‡LSD values may be used to separate means within a column.

Table 3. Pod yield and brix levels of edamame soybean treated with lactofen at 6 oz/acre plus NIS at 0.25% v/v plus 28% urea ammonium nitrate at 1 qt/acre at the R1^† and R5 development stages in 2002 and 2004. Pods were hand harvested at the R6 stage of development.

^†R1 = beginning bloom, R5 = beginning seed, and R6 = full seed as outlined in Fehr and Caviness (1985).
^‡LSD values may be used to separate means within a column.

Table 4. Seed concentration of genistein, daidzein, glycitein, and total isoflavone of soybean cultivars treated with lactofen at 6 oz/acre plus NIS at 0.25% v/v plus 28% urea ammonium nitrate at 1 qt/acre in 2002 at the R1† and R5 stages of development in 2002 and 2004. Seed isoflavone concentration was measured for each cultivar and lactofen application stage mechanically harvested at R8.

^†R1 = beginning bloom, R5 = beginning seed, and R8 = full maturity as outlined in Fehr and Caviness (1985).
^‡LSD values may be used to separate means within a column.

Table 5. Seed yield of cultivars in 2002 and 2004, and soybean treated with lactofen at 6 oz/acre plus NIS at 0.25% v/v plus 28% urea ammonium nitrate at 1 qt/acre applied at the R1† and R5 development stages.

^†R1 = beginning bloom, R5 = beginning seed as outlined in Fehr and Caviness (1985).
^‡Treatment means are averaged across lactofen application stage. LSD values may be used to separate means within a column.
^§Treatment means are averaged across cultivars and years. LSD values may be used to separate means within the column.