Sooty Rhodies?

[Swampster]

Any ideas, I have been suggested a few possibilities but nothing seems certain. The client has actually 'washed' a smaller individual plant and it has not re-occured. This isn't possible en-mass and this is every-where it seems. I'm not necessarily looking for a treatment, a solid ident would be good, thanks.:confused1:

[Graham]

Are they under sycs? Could just be sooty mould growing on the sugars aphids excrete.

[Swampster]

No,a beech stands over a portion of the stand and some birch elsewhere but there is no variation in the density of this sooty covering. it only covers the overwintered leaves and as you can see, the new growth is clear at the moment.

[Andy Collins]

Looks similar to a fungi called Erysiphe, though the colouring looks wrong, (should be more buff-coloured).Erysiphe is prevalent when there are dry soil conditions and the leaves have been watered. Treat with a suitable fungicide, keep plants well watered and mulched, avoid overhead watering. Hopefully this will help, even if the exact fungi is not quite accurate.

PS http://en.wikipedia.org/wiki/Erysiphe

Edited May 28, 2011 by Andy Collins

[Fungus]

Looks similar to a fungi called Erysiphe, though the colouring looks wrong, (should be more buff-coloured). Erysiphe is prevalent when there are dry soil conditions and the leaves have been watered. Treat with a suitable fungicide, keep plants well watered and mulched, avoid overhead watering. Hopefully this will help, even if the exact fungi is not quite accurate.

 

Erysiphe species produce whitish patches of powdery mildew on leaves and do not cover leaves totally with blackish layers, which can be washed off.

As I'm not even 100 % sure, this is a plant pathogen, IMO it would be best to identify the cause first before using a fungicide.

[Andy Collins]

Oh well, back to the drawing board, it was sort of a stab in the dark anyway

It appears upon a little light reading I had my wires crossed somewhat. The fungi Erysiphe being a result of powdery mildew, whereas the sooty mould fungus is a non-parasitic fungus growing on leaf surfaces with honey-dew from sap-suckers Aphids etc. So control the aphids, and you control the sooty mould! I am humbled before you Gerrit :adore:

[easy-lift guy]

Spray with 1 ts of dish washing liquid to Gal of H20. Graham is correct, I believe the plant looks to be a Rhododendron?. This build up will not harm the plant and I have seen it thousands of times. Spray once a week both sides of leafs. Good Hunting

elg

[Len Brennan]

It's sooty mould caused by Rhododendron cushion scale. If you look on the underside of the leaves you'll see small white clumps which are the scale insects covered with a protective coating. As they grow they secrete 'honeydew' like aphids and that causes the black mould on the leaves below.

It's tremendously difficult to get rid of especially if it's widespread. You could try spraying with soft soap but it won't get rid of it completely. Systemic insecticides seem to be the only real control method.

Have a look here Cushion scale / RHS Gardening Advice

[Swampster]

Thanks to you all. I shall get on the case and report back the results.