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If you live in a northern European climate but have accepted the challenge of growing an orange tree then be prepared for certain amount of heartache, some of it justified, some not. One of the things that is alway a concern is the yellowing of the new growth. The young leaves emerge in the spring a wonderful burnished, bronze colour, but once they fade to their regular vivid, mid-green colour they can often continue to change to a rather unhealthy yellow as the leave grow to their full size.
|Iron Deficiency - http://www.yates.com.au/|
If the new growth is showing green veins with the rest of the leaf appearing light yellowish to white in colour then this is iron deficiency. If the new growth is pale green to yellow in colour the this is sulphur deficiency. If the leaves have a weird-looking inverted green V-shape at the base surrounded by yellowing then this is magnesium deficiency. If it is the older leaves that are turning yellow first and then followed by the newer growth then it s likely that nitrogen deficiency is the problem.
|Nitrogen Deficiency - http://idtools.org/|
Before commercial acidic fertilizers were available, epsom salts (magnesium sulfate) were a popular method of treating yellowing citrus leaves. A tablespoon of Epsom salts dissolved into half a gallon of water, should do the trick and this too can be applied as a foliar spray. The magnesium in epsom salts addresses magnesium deficiency while the sulphur helps to acidify the rooting medium. What about iron deficiency I hear you say? Well it was traditional to add iron nail or iron horse shoes to the ground before planting.
|Magnesium Deficiency - http://www.grantsgardens.com/|
If your orange tree is not only showing a yellowing of its leaves but also other worrying characteristics such as a gummy inner bark, dry cracked bark with sap oozing lesions then it is probably suffering from one of several fungal diseases. Spray immediately with a systemic fungicide and withhold watering. If your orange tree is also suffering from die-back and dropping leaves then it is possibly under attack from honey fungus. Scrape away at the surrounding soil and if you uncover thick, licorice-like, bootstrap roots then your plant has been infected with honey fungus. Dig up and burn your orange tree to control the further spread of the fungus. Drench the surrounding soil with armillatox.
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