Q: Hi Bob, we have a Queensland Bottle Tree which is about 6-8m tall.
It has, over the last month or so, developed sooty mould (I think - it appears to be covered in a black dust). It's difficult to see as the crown is about 4m above ground.
I know sooty mould results from aphids and is more common in dry weather - but any suggestions on how to spray an entire tree with white oil/alternatives. It seems to be losing leaves fast...are we in danger of losing the tree? I don't recall it losing all it's leaves before. Thank you. Yvette – Toowong
A: ‘Black dust’ covering the leaves is a sign of sooty mould. If you have sooty mould on the leaves of your Bottle Tree you should also have the ‘black dust’ covering parts of the ground below your tree.
What happens is that certain insects excrete a substance which is termed ‘honey dew’. This is sugary and sweet and covers the leaves of the insect infected plant and also drips down onto the ground and onto whatever other plants that happen to be below. The honey dew is an ideal, nutrient-rich substance for the fungus, sooty mould, to grow on. To control sooty mould you need to eliminate the insect causing the problem in the first place.
It is not just aphids, Yvette, that cause sooty mould. There are other insects too…a few of them being scale, lerp, mealy bug and leafhopper. You need to try and identify the particular insect that has infected your tree. It happens, quite often, that more than one species of insect infects a plant at the same time.
These two pictures of Bottle Trees (in Roma Street Parkland) were taken on the same day…one tree was severely affected by scale (the top picture), whilst the other had no problem whatsoever (the bottom picture).
My suggestion is to drench the root zone of your tree with Confidor. When I say ‘drench’ I mean really DRENCH. Confidor is a ‘systemic’ insecticide, which means that it gets taken up and is absorbed into the plant’s internal systems and is spread throughout the plant. It will affect whatever insect is susceptible to the insecticide, and all the insects mentioned above will succumb.
White Oil may not control all the insects responsible for sooty mould, and has to be sprayed onto the plant in sufficient quantity so as to smother the insects with it. Confidor will control most of them. Bottle Trees are very resilient, and you should not lose your tree. Even without sprays, at most times, a Bottle Tree will withstand the problem.
An aside: In these ‘dry times’ you will probably find that whatever you pour around your tree will simply flow away, without the soil actually absorbing much of the moisture. May I suggest that you read my answer to Julia – St Lucia on "Soil not retaining water". I suggest that you water your Bottle Tree thoroughly, and soak the surrounding soil and make it absorbent, before you drench with Confidor. We need the Confidor to be absorbed by the soil, so that your tree can then actually ‘take it in’ through its feeder roots in the soil.
