Peach Tree Response to Low-Dosages of Dicamba as Repeated Applications or with Various Spray Nozzles

Two low-dose dicamba exposure trials were conducted on container-grown peach trees in Fayetteville, AR. Peach trees were ‘July Prince’ scions grafted onto ‘Guardian’ rootstock and were transplanted into 19 L containers and received experimental dicamba treatments in each year. Container trials were initiated in 2020 and repeated on new trees in 2021. In the repeated application trial, dicamba was applied at 5.6 g ae ha-1 (1/100× field rate) in five sequences: an untreated control receiving no herbicide, one treatment receiving only initial application, and three treatments receiving initial application plus sequential applications at the same rate occurring 14 d, 28 d, 14 d + 28 d after initial treatment (DAT). A separate trial assessed peach tree responses to dicamba applied at 11.2 g ae ha-1 (1/50× field rate) using a selection of nozzles with differing droplet spectrum characteristics: Turbo TeeJet® Induction (TTI11002), Air Induction Turbo TeeJet® (AITTJ60-11002), AIXR TeeJet® (AIXR11002, air induction extended range), XR TeeJet® (XR11002, extended range flat fan), and XR TeeJet® (XR1100067, extended range flat fan). Peach tree height, tree cross sectional area (TCSA) and leaf chlorophyll content were not reduced in response to any sequence of dicamba application or nozzle selection. Repeated applications of dicamba at 1/100× rate did not increase peach injury after 28 DAT. By 84 DAT, no effect of nozzle type on peach tree injury was discernable, and all treatments caused below 4% injury. No dicamba or dicamba metabolites were observed in leaf samples collected at 14, 69, or 85 DAT from trees treated with XR1100067 nor in untreated controls. While peach tree injury was observed throughout the experiment, dicamba residues were only detected consistently in 2020 from leaf samples of trees treated with dicamba at 1/50× rate using TTI1102, AITTJ60-11002, AIXR11002, and XR11002 nozzles.