I have two enquiries about related problems. See the edited letters below:-
Nancy, Legian writes: I’m in tears over my papaya tree plantation: They have a disease which looks like mould from a distance (white powder), but in fact
they’re tiny insects. Someone told us to scrape the bark thoroughly applying a product to kill the insects but I’m not impressed with the result. That was the trees; but now my fruits are also sick with big white pimples. On top of that they’ve been half-rotten for a whole season. Please help!
Emma, writes: I have been living in Bali now for 19 years and love the garden very much, spending many hours in the garden. On several occasions, I have come across a problem where leaves on my trees turn black. I tried spraying milk and yoghurt on them with little success. I was then advised to get Neem Oil from the Sunrise School but it never left. I moved gardens but again in one corner of my garden the black stuff has appeared. I have been cutting all the trees and bushes back but still it persists. Is there something that actually works?
Then on the other side of my garden a white ‘thrush-like’ fungus started to cover my trees, not big trees, and a palm tree, I also cut that back as it was curling the leaves and it looks like it is eating away the stem.
My ‘so-called’ gardener who comes ones a week, took a sample to a nursery and came back with a chemical and started to spray this on the tree once a week. That was three weeks ago, but it is still there. I keep cutting away but now the trees are becoming rather small with all this cutting.
The nasty white ‘stuff’ is not a fungus, but a sap-sucking insect - the aphid. The white kind are ‘woolly aphids’ and are common here, especially at this time of the year (start of the dry season) but can be a pest at any time.
One aphid can give birth to 50+ live young (very tiny) and lay hundreds – if not thousands, of even tinier eggs. Consequently they multiply rapidly. Treatment requires daily spraying. If the chemical Michelle’s gardener bought was a fungicide it will have no effect.
There are insecticides available commercially (but rather expensive here) – the most eco-friendly being made from the African pyrethrum daisy or its synthesized chemical relations. More environmentally friendly is soapy water. Buy several tablets of soap which contain 10% sulphur. ‘Melt’ them in warm water until they become a stiff jelly. Dilute the jelly with water (two tablespoon per liter). The soap clogs the breathing pores of the aphids and they quickly die but are rapidly replaced by all those eggs.
Aphids and scale insects are both dealt with in this way. The sulphur is also effective against rust which is a fungus-type infection. This can be seen usually on the underside of leaves (especially frangipani) as an orange/yellow powder. This is the spore body and floats everywhere on the slightest breeze.
Both aphids and scale secrete nectar. Ants ‘farm’ these insects and I am sure you will find many ants around affected plants. If you have the patience, you will see ants ‘tickling’ these insects to stimulate nectar flow. Aphids like soft, newly emerging shoots and tend to concentrate around growth points of the plants. As leaves grow, they migrate to the lower surfaces. As they suck the sap, they divert the nutrition from the plant, so leaves are often deformed.
Cutting the plants back often as Michelle has been doing is not such a good idea – better to treat the cause and only remove individual leaves which are beyond saving. An affected leaf can still photo-synthesize and feed the plant; cutting back hard only weakens it further.
The ‘nasty black stuff’ is known as ‘sooty mould’. It doesn’t suck sap itself; rather it lives on the excess nectar produced by aphids/scale. If Michelle had sooty mould without any sign of aphids, it is most likely that her trees/shrubs have scale insects. Whereas the soft body parts of aphids are very sensitive to treatment, scale insects cover themselves with a hard, translucent coating which resists treatment. If the nectar flow ceases, the mould will die. Remove dead sooty mould with a strong jet of water.
Scales look like little shells stuck to twigs, branches and sometimes quite large boughs. Look for them Michelle but you will need a magnifier (glasses/handheld) to be sure of seeing them. They may be removed by scraping, but this is a tedious business and often they are missed. There is oil of some kind in all soaps, but a bad infestation may need twice daily spraying.
If it is a consolation, I also have the woolly aphid problem. I save trigger operated bottles when empty, fill them with soapy water, and have several placed strategically around my garden. At least daily, I go on patrol and if I see the signs, give the offenders a quick squirt.
Please send all your gardening questions to
E-mail: gardendoctor09@gmail.com
