Deposition and retention of chlorothalonil (CTL) on peanut (Arachis hypogaea L.) foliage was evaluated by surface-stripping leaf discs with toluene and determining the CTL concentration via gas chromatography. CTL was applied at 1.25 kg/ha via ground sprays, a center pivot-mounted underslung boom, or chemigation in 0.12, 1.7, or 17.8 kL of water/ha, respectively. Ground sprays resulted in the highest concentrations of CTL on peanut leaves followed by the underslung boom and chemigation, respectively. Residue levels were lower with the higher volume applications but were more uniformly distributed throughout the plant canopy. Deposition of chemigated CTL applied as Bravo 500(R), Bravo 720(R), or Bravo 720(R) plus either an emulsifiable vegetable oil (SoyOil 937(R) or a nonemulsifiable petroleum oil (UN Sunspray oil(R)) was also evaluated. Results of residue sampling at 0, 5, 9 and 14 days after treatment indicated that addition of either oil to Bravo 720(R) resulted in the highest initial deposition of fungicide followed by Bravo 500(R) and Bravo 720(R) alone, respectively. However, the half-life of CTL applied as Bravo 720(R) plus either oil was reduced as compared to the half-life for either Bravo 720(R) alone or Bravo 500(R). By day 14, concentrations of CTL had decreased by more than 93% in all treatments. The mean half-life of CTL for all treatments was 3.8, 4.8 and 4.8 days in the top, middle and bottom canopy layers, respectively.

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Author notes

1Support for this research was provided by State and Hatch funds provided through the Georgia Agricultural Experiment Station. Additional funding was provided by Fermenta ASC Corporation.