Canterbury
June
Q.
My lemon tree has black mould on the leaves where the sun doesn't get to, and it is also in direct line of outside heat pump unit. What do you suggest?
Sandra
A.
- That is sooty mould, it is caused by sap sucking insects such as scale insect, whitefly, mealy bug or aphids.
- Ants may also be crawling over the tree, they are feeding on the honey dew that is excreted when these insects feed. It is the honey dew that the sooty mould is living on.
- Eliminate the insect problem by spraying with a suitable horticultural spraying oil or a pyrethrum based spray. Talk to your local garden centre or hardware store about a suitable control.
- The sooty mould will go away once the insects are under control.
- Spraying the tree with milk will remove the sooty mould, it will flake and washes off in the rain, but you need to control the insects otherwise it will keep coming back.
Read the Tui Citrus Grow Guide
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What is the black mould on my lemon tree? Comments
I see our good orange tree in the Nelson/Tasman area struggling with black soot. I have used Neem oil a couple of times. Do I need to use milk only or can it be watered down somewhat? I very much hope this method will keep it alive. Many thanks, kind Regards Luregn
Luregn
Hi Luregn, the sooty mould is there because you have sap sucking insects such as scale, aphids, or mealy bug on your tree that excrete honey dew as they feed. You may find ants on the tree too, they also feed on the honey dew. Sooty mould is spread by wind, it lives on the honey dew and while it doesn't kill the tree, looks unsightly and reduces the vigour of the tree. If you control the insects the sooty mould will eventually disappear, and can be cleaned up by spraying the tree with undiluted milk or better still, use a horticultural spraying oil that will also control the insects, repeat applications may be required. Eventually the sooty mould will wash off with rain.
Lianne