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| Nutrient disorders Not much is yet known of any nutritional disorders for cherimoya trees grown in New Zealand. Some studies suggest there is a high requirement for zinc (Zn). Symptoms of Zn deficiency include restricted terminal growth, small leaves, and interveinal yellowing of leaves, which can be corrected by applying zinc sulphate at a rate of 25–30g/m2 under each tree, in a 30cm band inside the drip line. Note that yellow leaves could also mean that the soil is too dry or the weather is too cold, not always a disorder that needs a fertilizer. In Australia, boron (B) deficiency is thought to cause hard brown lumps to form in fruit, particularly around seeds which has been corrected by application of 2g borax/m2 beneath each tree. Even application and sufficient watering is essential to avoid tree damage. Alternatively a mixture of 300g borax/100l of water can be sprayed onto mature spring growth, although foliar applications aren’t as effective as soil applications (but they are safer). In New Zealand, cherimoya aren’t likely to be planted in areas where soil is naturally low in B. During a greenhouse study of cherimoya planted in sand, lack of calcium was the first nutritional deficiency noted. Next – irrigating cherimoya trees
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