`Petite Yellow' dwarf ixoras (Ixora spp.) were grown in an alkaline substrate (3 limestone gravel: 2 coir dust) or a poorly aerated composted seaweed substrate to induce iron (Fe) chlorosis. Chlorotic plants were fertilized every 2 months with soil applications of 0.1 g (0.0035 oz) Fe per 2.4-L (0.63-gal) pot using ferrous sulfate, ferric diethylenetriaminepentaacetic acid (FeDTPA), ferric ethylenediaminedi-o-hydroxyphenylacetic acid (FeEDDHA), Hampshire Iron (FeHEDTA plus FeEDTA), ferric citrate, iron glucoheptonate, or DisperSul Iron (sulfur plus ferrous sulfate). Additional chlorotic ixoras growing in a substrate of 3 sedge peat: 2 cypress sawdust: 1 sand were treated every 2 months with foliar sprays of Fe at 0.8 g·L-1 (0.11 oz/gal) from ferrous sulfate, FeDTPA, FeEDDHA, ferric citrate, or iron glucoheptonate. Only chelated Fe sources significantly improved ixora chlorosis when applied to the soil, regardless of whether the chlorosis was induced by an alkaline substrate or a poorly aerated one. As a foliar spray, only FeDTPA was effective in improving chlorosis in dwarf ixora. Leaf Fe content either showed no relationship to plant color or was negatively correlated with plant chlorosis ratings.
Timothy K. Broschat and Monica L. Elliott
Foxtail palms (Wodyetia bifurcata Irvine) were grown in 6.2-L containers using a 3 calcitic limestone gravel: 2 coir dust (by volume) substrate to induce Fe chlorosis. Plants were treated initially and 2 and 4 months later with soil applications of FeDTPA, FeEDDHA, FeEDTA+FeHEDTA on vermiculite, FeEDTA+FeDTPA on clay, ferric citrate, ferrous ammonium sulfate, ferrous sulfate, ferrous sulfate+sulfur, or iron glucoheptonate at a rate of 0.2 g Fe/container. Similar plants were treated initially and 2 and 4 months later with foliar sprays of FeDTPA, FeEDDHA, ferric citrate, ferrous sulfate, or iron glucoheptonate at a rate of 0.8 g Fe/L. After 6 months, palms receiving soil applications of FeEDDHA, FeEDTA+FeHEDTA on vermiculite, FeDTPA, or FeEDTA+FeDTPA on clay had significantly less chlorosis than plants receiving other soil-applied Fe fertilizers or untreated control plants. Palms treated with foliar Fe fertilizers had chlorosis ratings similar to untreated control plants. Palms with the most severe Fe chlorosis also had the highest levels of leaf spot disease caused by Exserohilum rostratum (Drechs.) K.J. Leonard & E.G. Suggs. Neither chlorosis severity nor leaf spot severity was correlated with total leaf Fe concentration.