Monday, 13 July 2015

A Drastic Solution

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.
Sooty mould.
I did spray with a soap water solution last year when I discovered the mould, but in actual fact the mould, which forms on the honey-dew secreted by the pests, will dry out and crack off eventually but if you have several large bushes facilitating this is more than a labour of love! The mould does not cause physical damage to the leaf but restricts photosynthesis from happening and is therefore detrimental to plant growth.

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!
 The wall has also been cleared of ivy which ran down under the rhododendrons as a stem only, to reappear at the edge of the drive where it once again produces leaves. The ground is so far only partially cleared and I have also revealed that parts of the wall are going to need some re-pointing in the near future (One job always leads to another!). Several more plants that were affected have been cut down and as they are all "rough-barked" rhododendrons I expect them to grow back initially at a size which, should there be further outbreaks, is manageable to control although there will be no flowers for a couple of years. I have several camellias nearby which are also a target species, so far they are untouched but I have sprayed them to be on the safe side. 
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?