Zinc and manganese chelate toxicity on nursery and seedling peach trees

Abstract

Because of claimed damage from use of combined ZnEDTA and MnEDTA in young budling peach trees in a nursery, field and laboratory tests were conducted to evaluate the potential toxicity from the chelates. An experiment was made in a commercial nursery with peach trees with three different rates of application besides a control (3.36 and 1.12, 13.44 and 4.49, 33.60 and 11.21 Kg/ha of Zn and Mn both as EDTA chelate). Soil pH was near 8, soil was calcareous and high in clay. The treatments were shanked in 15 cm deep and at distances either 18 or 7.5 cm on both sides of row centers. Applications were made on April 7 and trees had been budded in October previously on seedlings (Nemaguard) germinated in the previous spring. Contrary to predictions but related to time and conditions of applications, the highest two application rates resulted in death or injury of most of the buds. The lowest application rate resulted in some leaf burn at the close shanking rate and particularly on trees in parts of the plot with poor soil which resulted in considerable Fe deficiency. There were varietal differences. There obviously are critical concentrations or dilutions at which ZnEDTA and MnEDTA together can result in damage and the effects of ZnEDTA and MnEDTA appear to be additive. Injury was associated with increased levels of Zn and Mn in leaves. Iron, copper, aluminum, silicon and titanium were also elevated in leaves as occurred for leaves in the nursery involved in a law suit over chelate damage. This phenomenon is explained in detail. A conclusion is that label directions for such use of chelating agents need revision to minimize the possibility of having high concentrations of metals around plant roots in either wetting or drying cycles.