We have a purple Rhododendron next to a spindle tree under a huge birch tree. Our neighbour put up a 5ft fence and last year there was a black soot like stuff on a bit of the bush. White almost chalky stuff underneath. We got it all off but now every leaf under the top growth is black.....The plant is 30 yrs old. Any ideas please!
Cheers for that. There are no white sapy or fungus yet. Just seen tiny black spots on a brand new rose 40 feet away. We had a hawthorn hedge between ,,,the fence is higher ....spindle tree branches are quite dark with no leaves yet
Little black spots on roses could be aphids (do the spots move? Are they on the new buds, before they open?) or a disease called 'Black Spot' (Shows up on leaves.)
You might google for some images of each.
First of all, there has been a lot of shade added to the old Rhododendron, they don't like early morning sun as when buds get hit by frost, then the sun comes out the buds get defrosted too fast and they die off.
There are several diseases that attach these plants and one as stated before is sooty mould,
but the one you are seeing is what Cville has mentioned, Sooty Mould, this is caused by the Azalea / Rhododendron White fly, they suck the sap from the leaf and there droppings cause a honey fungus that turns Black, You need to go to garden store for a product specially for BLACK sooty Mould and spray the leaves AND the undersides as that is where the bugs feed.
If you don't want to go down the Chemical way, use washing up soap, take a bucket of this mix, water and soap, use an old sponge and hold the underside of the blackened branches and one hand under the branch for support, and wash the leaves with the soaked sponge in other hand. it laborious, but it works, I have many Rhododendrons, don't like using chemicals unless I have tried every other safe way to treat a plant infestation, but found the washing up soap to be the best, have the hose with you to rinse as you rub the mould, redo if you have to.
Lastly, any leaves that have dropped need to be raked up and burned or the mould with spread by spores. the problem spread's over time.
Give the Rhodo more light and this may mean lopping some branches off the Tall Beach tree to lift the canopy allowing more light onto the Rhodo also helps it produce more flower buds, these are formed after the flowers die off so IF you prune Rhodo's, you remove the following years flower buds. Last resort is to really cut back all the affected branches on the Rhodo and BURN them, give a good feed with suitable properties for ACIDIC loving plants, it will form new re-growth and give water often too, because the tree's are the stronger plants are any water where it falls will be taken away from the Rhodo as the tree roots are wider spread and demand more water.
The Rose Black spot is a different disease affecting Roses, you remove the infected leaves and BURN them as this disease overwinters in the soil where the dead leaves have dropped.
There is a spray you can buy, but in my own garden, removing the leaves and new ones regrow, is best way to go, this Black-spot will NOT kill the roses but it can become un-slightly IF left to spread.
Hope this gives you some insight and you can get on top of the different problems.
Best Regards. WeeNel.
Nice reply cheers!! Computer went down so I started over....remembering passwords is a pain!!
The beech tree is at the side of the garden & its as tall as a house....the fence cuts off air circulation i guess....an enkianthus next to rhodo is clear.....we have a dog so i will use white vinager & washing up liquid....no insects yet.....rhodo is with us 22 yrs...i moved it away from a sycamore tree!!! back then....
I've never done anything to treat sooty mold, which has always gone away on its' own. It's a seasonal thing *some* years.
Vinegar is often recommended as a weed killer, be careful putting it on desired plants.
I would be inclined to try move the Rhodo again into more light, not necessary Bright sun but a better natural light. to do this move with a large shrub you either need to wait till after flowering time, or late autumn.
Use spade to slice through the soil in a circle all around the root are about 2 feet from the main stem, as you trench make sure you rock the spade back and forward to make a space, fill this space with nice peaty soil and new soft roots will regrow into this,
the following year, you make ready the new planting hole dig much deeper and wider than required and put as much humus into the planting hole as possible then start to dig out the Rhodo shrub, when out of the soil, place on an old sheet or plastic to make it easier to pull/drag the shrub, NOT A ONE MAN JOB, make sure when you replant the shrub in new planting hole you firm the soil around the root area as you go, give plenty of water and make sure the soil is never allowed to dry out for the first season.
I know this is a long drawn out procedure but, you might regret next year IF not taking action.
The Rho is huge over 6ft tall 7ft wide 5ft deep to the fence. The purple flowers are generally fantastic. The underside of the leaves is good...just the black....I will reach all the leaves to clean them up. Sun hits in the morning....Its warm as we eat out nearby
The black is VERY thick & on some leaves there is a crust. New top branches are OK. I had a go spraying & cleaning....spraying needs every leaf rubbing but nothing doing. I use a finger nail & scrape off sadly some leaves tear.....No sign of insect on undersides.......On the black leaf areas the flower buds are missing or stunted...... The Enkianthus is in full bloom on the left & I don't want to spray too near that!!!!
After the plant has finished flowering, I would prune out ALL the stems that have the blackened leaves, by next spring the cut out area will have new shoots / leaves taking up the space left from your pruning.
By doing this after flowering, you still give the plant enough time to grow new leaf and new flowering shoots too, As you may already know, Rhododendrons start to produce the next years flowering buds as soon as this seasons flowers have faded, I try to deadhead all my Rhodo's IF I can reach the top as it is a lot of energy being used up making seeds as well as new flowering buds.
Around September time you look close at your shrub and you will see the fat flower buds being formed, they look like fat green berries / pods, right at the tip of branches, so by cutting out the damaged branches you are leaving enough time for any new growth to develop.
Make sure you burn the damaged diseased pruning's as you don't want the spread of further areas to be affected.
Hope this helps you out a bit.
I can no longer see the plant from the house as enkianthus is bigger & in front.....the "black is under all & at the sides...my tribe is reluctant to get wet & do a pic...
Forget the pruning the blackened branches, there is far toooooo much damaged leaves,
I would wash off an area at a time with warm soapy water, dish washing-up liquid would be the best to use as the warmth will help dissolve the black sooty mould and the soap will help it slide or be removed, rinse sponge after each lot of leaves have been wiped / washed by frequently squeezing it in the soapy or you will just be painting it back onto leaves again.
You don't have to get the whole shrub washed in one go BUT, as you have a spare half hour a day, go do another area. You will though have to allow much more light and air movement to circulate the plant as it is obviously being hemmed in by the neighbouring plant and these are blocking light, air and possibly even steeling the nutrients from the soil.
It appear a shame to loose a lovely old shrub while tending others in the same vicinity but Hey, I look at the cost of replacing a Rhododendron and know that would be my first choice to save.
Hope this helps you out a bit more.
In the areas I washed there new shoots ..The plant is about 8ft tall....the black is on the left a bit
on the right at the back a strip of 1ft down....bottom line underneath.......I guess it all started when a fence went up
You can make out the purple ....the pink rho is much better....2 bad leaves before it flowered....about 6ft high.....big flower heads
I cant impress on you enough that the Rhododendron is suffering from lack of light and air circulation, with all the stuff growing sooooo close to it and taking into account the age of the plant, the root spread this age also has, there is no other way you can prevent the black returning even IF your able to clean it off.
it's a shame that such a lovely plant struggles to give of flowers yet struggles also against sooty mould disease.
Hope it all turns out for your plant before long.
Sooty mold may be a common name for different problems, but here is what I think is going on.
When aphids and certain other pests suck the juice out of the plants they digest it, but not very well. What they excrete still has a high sugar content. They excrete this all over the leaves, and it drops down onto plants below.
Then a fungus grows on the sugary waste. This is sooty mold, here in CA. Looks EXACTLY like your pictures.
The treatment is 2-phase:
You can keep cleaning the leaves all you want, and that can help.
But the real 'treatment' is to reduce the pest population that is excreting all the sugar water.
Look on the Rhody itself, and on the plants above it. Look for aphids, scale, whiteflys and probably a few other pests. When you find the pest you can figure out how to deal with it.
Thanks again. Even some new shoots & stems are like soot. The fence stops air circulation.Next door there was a hawthorn hedge that I was really badly allergic to. The doctor once came out to give me antibiotics at 5 am otherwise I'd have lost a finger or two...I have scrubbed but rain stopped me in my tracks. I will remove all debris too....I thought it was a good mulch.......White fly lay on the underside leaves 2 yrs ago...nothing yet! cheers