g'day poso02,

sounds like the tree is infested with either scale insect or mealy bug?

either way look for the ants they will have bought either or both bugs onto the plant.

once you move the ants on then you can treat the bug if you want or simple leave it, won't do a lot of damage to the tree. there is a homemade white oil recipe on our web page. use it after the sun and generally i recommend at 25% the recommended rate.

len

Here is a link that might be useful: lens garden page

Gardenlen,
It intrigues me how you spray your eucalyptus tree with white oil...you must have a pretty big ladder or own a helicopter, now c'mon, come clean, how do you do it?
Jim

Perhaps one of those hose attachment sprayers?

well jim if the tree is that tall then maybe it should not be anywhere near the house, and in the case of mature trees treat the ants and let the tree look after itself. the original poster gave no indication to stature of tree.

so i just offered up the standard procedure for dealing with the infestation.

oh and i don't/would never have a eucalypt forest type tree in my suburban yard just not the right place for them.

at this stage i leave it up to pos02 to determine how they treat their tree if it is over say 2 meters high.

len

The tree is probably 15m or so. It is away from the house, but some of the larger branches are above the concrete, where it leaves black residue. The reason I am blaming the tree is because the concrete does get the hot western sun, so it cannot be some sort of moss (??). The roof of the house is also somewhat affected, however the tree does not extend this far. Maybe it is not the tree after all. I have had the tree inspected by council horticulturalists, and they say it is very healthy.

lichen?

the tree can still be infected by say scale insect and still be considered healthy. but it is sounding like something else because i would expect if sooty mould was going to spread for the activity of scale there would need to be a lot of scale evident on the tree. you can get a black mould that will grow on roofs.

the safety margin for forest trees especially gum trees from houses and out buildings & overhead utilities is considered to be the maximum height of the tree + 50%, from what i saw when i was in rural i would go +100%.

if it where thrips a tree that size will look after it self, the ants will eventually move and thrips will die out.

len

Which Eucalypt is it? The Eucalypt in our area which is prone to that horrible black sooty stuff is the Cadarghi, Eucalyptus torreliana. It's such a nasty environmental weed anywhere south of Mackay that I have no hesitation in recommending that you cure the soot problem by chopping the tree off at the ankles!
And to add to its general offensiveness, it doesn't even make particularly good firewood!
Trish

Trish G,
I wish to apologise for my insulting outburst re what you wrote about the eucalyptus and should have read your, My Page before over-reacting and writing what I did.

the cadarghi gum has been turned into an enviro' weed by being used as an exotic native outside it's indemic area, as can happen with many natives of one region being weeds in another the mt morgan wattle is another that comes to mind, and i'm sure the alexander palm is having an impact on the native bangalow in the s/e qld region. and in the nature of things all mankind is a weed.

and any tree eucalypt, melaleuca, callistomon etc.,. etc.,. can be subject to infesting by sooty mould which is bi-product of scale/mealy bugs usually bought in by ants.

at this stage are we sure that pos02 has sooty mould?

len

Here is a link that might be useful: lens garden page

To add a bit more information, the mould (for want of a better word) gets slippery after a day's rain, and it can even be removed if you scrub hard enough. When it is dry however, there is no way of removing it, even with bleach. My dillema is that I intend to tile the area, and am worried that the tiles will eventually succumb also. If I sealed the tiles, would this make it harder for the mould to take a purchase?

g'day pos02,

if there is no way of treating the problem on the tree then haow about treating and removing the ants from the scene? once they are gone the scale whatever infestation will dissappear.

got no doubt the problem you now have on the cement will still be there when you tile, does using bleach help clean the cement off?

len

Here is a link that might be useful: len's garden page

whatever it is pos it sounds like its water soluble.have you tried hot soapy water to remove it? the mould sounds like its growing on something, it could be honeydew from scale or maybe sap which is why youre having trouble getting it off, but the sap or whatever its stuck to might come away with hot soapy water (let it soak in a while). or if that fails then try white spirits to see if it will dissolve and shift it.

I had a euc. where I lived in Sydney years ago (Eucalyptus Nickoli), about 6 metres from the house and under it a concrete path and steps. When it was mostly matured (about 10 to 12 years old) and with no noticable bugs except occasionally sawfly lavea infecting it, it still blackened the concrete and the steps terribly and i couldn't scrub it off. I put it down to the oils from the leaves and also the leaves falling on the concrete, though it didn't shed many of them. I resolved the only way to cure the problem was to cut it down and remove the root and take note not to plant eucs near concrete or houses again! They do need plenty of space.

g'day f.w,

the substance is sooty mould and though unsighted there would very likely have been scale or mealy bug infestation to cause that as it forms on the suagry substance that these bugs secrete that is why the ants farm them as well, so generally you will have ants paying close attention to affected plants.

and yes there is no room in or near gardens for those large forest type eucalypts, they present certain dangers ie.,. dropping major limbs and falling over almost completely unannounced and at times for no obvious reason.

len

Here is a link that might be useful: len's garden page

Yes, there could have been a bit of sooty mould, and although it would be over 25 years ago, I recall I did check over it for evidence of that, ie. ants; fluffy little bugs; scale but found no substantail evidence of it so I got some qualified advise (Sydney Royal Bot. Gardens) and was told it was probably due to staining from the euc's. oils. I currently have some scale infestation on 2 of a dozen nerium oleanders (the pink ones), which I grow as single stemmed specimens. I also have a rose garden and when I spray my roses, about once every 2 months or more, and my azaleas for azalea lace bug (the roses for aphids and blackspot) I also give these 2 oleanders a spray. A dash of labacid and a dash or two of the fungicide triforene. The triforene also works, you know, for ink spot desease on kangaroo paws. Both systemics and I don't think too obnoxious when used rarely to the environment. By the way, I had a look at your site, Len, and was impressed, good job Pal.

thanks pal,

we are always adding and upadting.

with the scale and mealies look for the ants, once you move the ants on then treatment of the bugs will diminish.

len

I'm just cutting up a healthy Eucalyptus tree that had got too big for where it was. I've noticed black staining appear after a couple of days on cut surfaces and underneath logs. I reckon it's an oil from the tree discolouring as it weathers.