In this area we are currently inundated with a virtual plague of Cushion Scale (Pulvinaria floccifera), in my case it first attacked last year although I wasn't aware of it until the appearance of sooty mould on the upper surface of the leaves of all my rhododendrons more specifically on the R. ponticum pictured below.
Coincidentally these plants are cut right down every five or six years and allowed to re-grow. They were scheduled for the chop last year although I didn't get round to it, so, rather than spend forever trying to clean the plants up, I decided that cutting them down, even at this late date was the solution.
|Cushion Scale egg masses.|
To control the pests something stronger than detergent sprays is needed, contact insecticides need to be sprayed to the underside of the leaf, so good luck with that if you have several large rhododendrons, the only sure method is to use a systemic such as thiacloprid or acetamiprid at the hatching time from late June to mid-July and even then repeat sprayings may be necessary.
|The ultimate solution!|
One reason put forward for the almost epidemic proportions of the infestation is the warm winters we have had, perhaps a cold one is due or should we be careful for what we ask?