Horrid infestation on my Philadelphus
They have covered all the leaves and damaged them. I noticed around after Easter. I should have tried to blast them away with the hose, I didn't. Why would they attack the Philiadephus? This didn't happen in the past. There is a giant cypress blocking out the light on the other side (neighbour's garden).
Do not despair though - I has something similar happen to a large sambucus elder, which was literally smothered in them. Gross.
I bought some online ladybird larvae (didn't have many ladybirds in my old garden, at that point) and hung the bag they came in, on my elder, thinking it wouldn't be much help.
I couldn't have been more wrong! A week later all the aphids were gone.
One word of warning though - my attack was so bad that there were also black ants swarming around the elder, as they like to 'milk' the aphids for their juices...nice...so first I bought something called Antstop (small plastic container with an ant trap killer inside, that blitzed the ants in 3 days) and then I applied the ladybird larvae.
If you have ants, then do this first, or you run the risk of the ants eating your ladybird larvae!
How old is your philadelphus? Perhaps it isn't at its happiest because of being shaded too much?
When any plant is more stressed, it is more likely to be attacked, usually.
By the way, after my experience, the ladybird larvae hatched and the new ladybirds laid their legs on the elder, so more larvae were born to take over.
And three years in, there was a nice balance in the garden, with ladybirds and lacewings returning to lay eggs around.
A spray bottle with soapy water (a very small amount of a pure soap like savon noir) that you blast every time you wander past will work. Not as dramatically, but after a week or two you’ll get your philadelphus back.
I used to rub them off, (as I am sure they clung on tighter if I hosed or sprayed them). It was really icky, but you knew you had got a lot of them if they were squashed all over your hand. And they stained.
I gave up and also disposed of the poor philadelphus.
Disposable gloves are quite useful these days for the squeamish
Sorry , Hope you find a solution Elizarose.
I think that you have to be very vigilant early on at the first signs, which I think we often miss despite best efforts.