Diagnosis and correction of iron deficiency in planted eucalypts in north-west Victoria.  H. T. L. Stewart, D. W. Flinn and J. M. James.  February 1981.  7 pp.  (unpubl.)

SUMMARY

Eucalyptus globulus ssp. globulus Labill. (southern blue gum), E. camaldulensis Dehnh. (river red gum), E. grandis Hill ex Maid. (flooded gum) and E. botryoides Sm. (southern mahogany), planted on a calcareous soil and irrigated with municipal wastewater, showed mild leaf chlorosis and stunted growth of some trees four months after planting. Within a further two months, most trees were affected by the disorder and some tree mortality occurred. Foliar symptoms of the disorder were inter-veinal chlorosis, spot necrosis and marginal necrosis. The healthiest foliage was in the lower crown and close to the stem.

A deficiency of Zn, Mn or Fe was suspected and foliar applications of these elements were made to row plots of 20 trees of each species on the most severely affected part of the study area. Applications commencing in May 1980 continued at weekly intervals for six weeks, with Fe being applied as FeEDTA (chelated iron). In September 1980, further row plots were established for three of the species and two applications of FeEDDHA (a more stable chelate at high soil pH) were made a week apart. Foliage was sprayed to visible wetness in all instances, and for the FeEDDHA treatment, the soil around each tree was also drenched. Foliage samples were collected from trees sprayed with FeEDDHA, and from unsprayed trees.

Trees sprayed repeatedly with Zn and Mn failed to recover, whereas those sprayed with FeEDTA made only a slight recovery and then became chlorotic again. Conversely, trees sprayed with a solution of 0.1% Fe as FeEDDHA made a marked recovery, and the disorder was therefore diagnosed as Fe deficiency. Foliage samples were analysed for extractable Fe²⁺ and total Fe, but the results were inconclusive. Other studies have also shown that the concentration of total Fe in plant tissue is a poor indicator of the Fe status of plants.

Also published:

Stewart, H .T. L., Flinn, D. W. and James, J. M.  (1981)  Diagnosis and correction of iron deficiency in planted eucalypts in north-west Victoria.  Aust. For. Res. 11 (2): 185-90.