In response to many questions about gardening and associated gardening problems, we are pleased to announce that Gardening in the Tropics has returned to the pages of Bali Advertiser. Ed.
D.W. – Kerobokan writes: The frangipani trees in my garden are very sick. They have dropped many leaves, and some are quite black. Flowers are few and many are deformed. How do I restore them to health?
This is a perennial problem with frangipani. If you look carefully you will find many ants on the trees. Other signs of infestation are little brown bumps about the size of a match head. Sometimes they are fluffy and white, rather like the tip of a cotton bud. These are scale insects – being ordinary brown scale, and cushiony scale respectively. These pests exude nectar; a sweet syrup which ants love.
Ants ‘farm’ the creatures by bringing babies to the trees which quickly become infested. The black stuff on the leaves is ‘sooty mould’ which depends entirely on the nectar to survive. Severe mould causes the leaves to die and fall off, as the process of ‘photo-synthesis’ cannot take place. Kill the scale, and the mould will die and eventually slough off. Not as easily done as one might think, as both scales are protected by a waxy coating protecting them against contact pesticides.
The quickest and most effective method of control is to use a systemic insecticide. For smaller plants, dilute as per instructions and spray on leaves, as green tissue absorbs the chemical into the sap stream. Add some dishwashing detergent, which helps spray ‘stick’ to the plant parts.
For older more mature plants, use a drill to bore a hole which slopes diagonally downward into the trunk. Place a small drinking straw into the open bottle. Put a finger across the top of the straw to keep the insecticide inside the straw and transfer it from bottle to hole. Release the finger, and the liquid will gush from the straw. Repeat as necessary but do not fill to the brim.
Stop up the hole - a small cork, some glazier’s putty; a well-chewed glob of gum will suffice. There are two reasons for doing this: One is safety! These systemic insecticides are toxic, even more so in their concentrated form. You want to prevent them from coming in contact with birds, small animals, or children. Fish are especially susceptible.
Systemics are absorbed by the human body through the skin, so wear protective gloves whilst doing this. If you spill any on the skin or clothing, as soon as you have finished the task, strip off clothing and put it directly into the wash (into lots of water if you don’t have a machine) and/or go take a shower.
Systemic insecticides don’t last forever. You will need to do it again at intervals recommended on the bottle, or when you see signs of re-infestation. While I cannot remember brand names Ace Hardware carry such insecticides here. These substances are required to have the name of the active chemical on the label. Look for small containers (100 - 150 ml usually) which contain the chemical ‘Dimethoate’. Used neat in this fashion, 10-20ml. will be sufficient.
Another less easily treated infestation is rust. This is a fungal disease rather than an insect pest. Again, look to the underside of the leaves for blobs of bright orange. This is the spore of the fungus. Touch it and it will powder, coating your fingers and releasing spores into the air to find a new host.
A very old-fashioned cure for rust is sulphur. It really must be wettable sulphur as annoyingly it needs to be applied to the underside of the leaf, so a spray of some kind is necessary. There are toilet soaps here which contain wettable sulphur – usually about 10% of the formula.
Allow one tablet of soap to one litre of water. ‘Melt’ the soap in the water – grating it first will hasten the process. If the resulting solution is too jelly-like to spray, dilute it with sufficient water to enable spraying. This will need several applications to eradicate the rust and you will need to keep a close watch for re-infestation as the spores are always floating around in the air.
Regular applications of fertiliser will result in rapid regrowth and re-flowering. Controlled release fertilisers are safe (but also relatively expensive). If you use cheaper preparations such as urea, remember a little often (ie monthly) is the best method. Too much at once may result in chemical ‘burn’ to the plant. Your time and efforts will be well-rewarded in terms of lushness of foliage, size and quantity of flower.
Please send all your gardening questions to
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