THE CUBAN FIBRELESS SOURSOP
SCIENTIFIC NAME: Annona muricata
FAMILY: Annonaceae
One of my favourite fruits, the Cuban Fibreless Soursop, has had the deserved reputation of being a 'shy' bearer. Wanting more of this lovely fruit, I decided to experiment with a zinc supplement to see if this had any impact.
While this exercise lacked the scientific precision and recording shown in many of your previous articles on various subjects, I would like to share the results with other members, as it appears I have achieved the desired end of dramatically increasing the yield of the fibreless soursop. I must add that that claim is made with qualifications which I will mention later.
My fibreless soursop tree is a 5½-year-old grafted tree (can I mention ? purchased from Exotic Groves Nursery) that has always done exceptionally well, hence is quite a large tree even though I manicured the top off it 2 or 3 years ago. Even though it has always thrived, I never had any more than 4 or 5 fruit on it, at various stages, at any one time. It would flower prolifically but set fruit scarcely, despite plenty of moisture, mulch, fertiliser, trace elements (including zinc), mill mud, ashes, and good drainage.
So in July of last year, I decided to put zinc around all my trees because of the general deficiency of this element in our soils. I was also aware that the Annona family of fruit trees like more zinc than most others. So in my yard that meant extra zinc for the rollinias, a seedling custard apple (not sure of the variety), the fibreless soursop and three fibre soursops.
The rule-of-thumb measure I used was a good handful (using glove) of the zinc supplement ZINC SULFATE HEPTAHYDRATE (generously given to me by a cane farmer friend) for every year of the tree's age. The stuff dissolved well in water although some of the large lumps had to be broken up in the water. I added 5 or 6 handfuls to a 2- gallon bucket nearly full of water and poured this around the drip line, stirring it well beforehand. Later I watered the tree well on a regular basis.
It was winter, so the tree didn't do much for a while, but to my delight, shortly before the spring flush I was looking at it one day and counted at least 30 young fruit, and I think there have been even more at any one time since then. Up until recently, the dry conditions were not conducive to good fruit development, so the extra fruit I have had have been on the smaller scale but good to eat. However, with the recent rains I've noticed plenty of better looking young fruit.
I use green ants as biological control of pests, but this costs me a percentage of the fruit which they spoil with their 'dairy cows' - those white wooly aphids, I think they are. By spraying lightly with white oil (in the can) on the reachable fruit I can keep them clean but I don't bother with anything higher up. I expect the green ant spoilage problem to decline now with full foliage and ideal growing conditions.
My other fibre soursops are looking excellent with the older tree producing plenty of fruit. The custard apple seedling of about 4-5 years looks marvellous and is producing plenty of flowers for the first time. The rollinias also look good. However my large avocado seedling tree did not like the amount of zinc it was given and went a bit light on in foliage for a while, but looks good again now. No other trees had any adverse effects from the additional zinc.
So it looks to me like a generous amount of zinc is the answer to the 'shy' bearing nature of the fibreless soursop.
A friend recently told me she has got fruit for the first time after using a zinc supplement even heavier than I did. However I would advise caution and suggest to readers contemplating adding zinc to start off with half the rate I used and, make the tree reach out a bit for it, too. Don't worry if you see dead grass where it was applied. I have seen no adverse effects (except the avocado) from the larger zinc doses I have used, but I would also have to say that it's early days yet.
Finally I would like to say that any larger applications of zinc should only be through the soil and not the foliage.
DATE: March 1992
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