Vol 120 (2007): Proceedings of the Florida State Horticultural Society
Krome Memorial Institute (Tropicals)

Effect of foliar applications of Ascorbic Acid plus Ferrous Sulfate on leaf greenness of 'Arkin' Carambola (Averrhoa carambola L.) trees

Jonathan H. Crane
Tropical Research and Education Center
Published December 1, 2007
  • iron defi ciency,
  • star fruit,
  • plant nutrition


The effects of foliar- or soil-applied iron on leaf greenness of 12-year-old 'Arkin' carambola trees were tested in a 1.4-ha orchard on calcareous soil at the Tropical Research and Education Center in Homestead, FL. Trees received a foliar application of ascorbic acid plus ferrous sulfate (foliar acid plus iron), soil application of EDDHA-Fe, or no iron as a control in two separate experiments. An organosilicone adjuvant (Freeway(R)) was added to the acid plus iron solution. In Experiment 1, trees were treated with foliar acid plus iron from 6 June to 21 July (four applications) and a chelated iron drench was applied to the soil on 12 June and 8 Aug. 2006, with control trees receiving no iron. In Experiment 2, trees were treated with foliar acid plus iron from 18 Oct. 2006 to 16 Apr. 2007 (seven applications) and the chelated iron soil drench was applied on 31 Oct. 2006 and 17 Apr. 2007. In Experiment 1, treatments were arranged in a completely randomized design with six single-tree replications per treatment, and in Experiment 2, treatments were arranged in a randomized complete-block design with three single-row replications, consisting of 35 trees per row, per treatment. Leaf greenness was assessed on three recently mature (young) and three older leaves per tree from two trees per replication with a transmittance-based chlorophyll content meter (SPAD meter) just prior to each foliar acid plus iron application. In Experiment 1, young and mature leaves of trees treated with foliar acid plus iron had significantly higher SPAD values than leaves of trees in all other treatments. In Experiment 2, there were no consistently significant SPAD value differences among treatments. However, the older leaves treated with foliar acid plus iron tended to have higher SPAD values than the EDDHA-Fe treated and control trees, although differences were not consistently statistically significant due to the large variability within treatments. Several days after the first, second, and third foliar acid plus iron applications, flowers abscised and the oldest mature leaves (closest to the base of stem) became chlorotic and abscised and immature fruit turned yellow and abscised. However, young leaves generally remained green and intact. In addition to within-treatment variability, the lack of significant differences in SPAD values among treatments may have been due to reduced tree growth and nutrient uptake during fall and winter when temperatures were relatively low, since carambola trees become quiescent below 20 C. Further investigation is warranted to determine the efficacy of foliar acid plus iron applications as a replacement for chelated soil drenches.