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?



19 comments:

  1. I practise cultural control nipping out the infected shoots on broad bean if there is blackfly but this is ridiculous!
    Just joking Rick, it is great that you can pass on your wealth of experience.
    I often advocate pruning for pest control. It can be very effective on a shrub such as Artemesia 'Powys Castle' when a shoot is black with aphid but the rest of the plant is only lightly infected. Cutting the shoot away can restore the natural balance with aphid predators.

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    1. I agree Roger, it is very possible that rubbing out small infestations of aphids between finger and thumb can work very well as a control. I have planted out some nasturtiums this year in containers and baskets which immediately attracted black-fly, although I was able to rub them out this caused unsightly physical damage to the leaves, I have subsequently sprayed a systemic. I am sorry I do not feel guilty about this and am now coming round to the way of thinking that if there was not so much emphasis on using "non-toxic" "green friendly" controls which are generally pretty ineffective we would not have the same infestation problems we have today. I was surprised that you didn't pick up on the allelopathy angle as I suppose that if the rhododendrons were truly toxic the ivy would never make it to the other side.

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  2. A problem here too Rick. For that reason, I only have 2 rhododendrons left in the garden and I'm not sure how long they'll last. Although small enough to be treated, I'm not sure it's worth the hassle. I keep a close eye on the Camellias and like yours no sign thus far.
    I think our milder winters mean a lot of more pests and disease prevail.

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    1. Hi Angie, I am so sorry I didn't realise that it was so far spread, in fact I am really surprised that you are affected up there. From the way you describe it you seem to be in a pretty desperate situation, I suppose if you are against spraying expensive chemicals then you have to accept the inevitable. Always look on the bright side if you remove the rhododendrons it gives you more space for new plants :-)

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  3. Totally gross Rick, haven't come across it yet, hope I don't. Very impressed with your Ponticum, and I keep telling people that Rhododendrons grow much better in the cooler weather in Aberdeen. Our ones just carry two or three flowers, initially thought the soil was not acidic enough, although there is no yellowing of the leaves.

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    1. Yes Alistair it is a bit of a shock when particularly the ponticums have been there for at least 40 years and never had a problem and are even regarded as somewhat of a pest. There should be absolutely no problem with growing rhododendrons in your area, they are big feeders and dare a say it a dressing of peat would not go amiss!!!

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  4. Gosh, I haven't seen that before ! It looks totally terrifying! You sound as if you will have beaten it very soon ! Best of luck !

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    1. Not good Jane so a drastic remedy was in order. The disturbing thing is that, although I thought this was fairly localised, Angie is reporting it as a major problem in Edinburgh.

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  5. I've never come across this in my own garden and thankfully I've never been brought little plastic bags with suspect leaves like that. Thanks Rick for blogging about this as I'll be forewarned for the future in case any of my customers have this problem.

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  6. Rosie I sincerely hope you never see it, not everyone is happy to take the drastic action I have and to clean it up is a lot of hard work.

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  7. I had this problem in my previous garden a good few years ago on a number of plants, including my Acer palmatum – which is said to be almost impossible to get rid of on an acer. My infestation looked in some places completely covered in white dotted eggs and mature scales. But I managed to get rid of it completely everywhere with Bug Clear Ultra (acetamiprid) even though it took several sprayings several years in a row. Never came back – until I had been 6 weeks in my new garden here, then I discovered white dots on the underside of my baby camellia. Ugh! I washed them away as it was just a few, will keep a good look for more, but I suspect a neighbouring garden has an infestation so it won’t help much to treat mine once, I will probably have to start a yearly spraying regime from now on. And yes, I do spray with pesticides when it is absolutely necessary, I always do it very late in the evening, after sunset when the bees have stopped flying around – and I hope I am doing it cautiously enough.

    I must admit I giggle a bit whenever I read or hear that greenflies can be eradicated by rubbing them out between your fingers. I have nearly 700 potted plants in various sizes from small to very big, almost all of them are attacked by greenflies or blackflies at some point. If you rub away aphids with your fingers they will be back after a few hours or at least the next day. My goodness, if I was going to control aphids in my garden that way I would not have skin left on my fingers, let alone any time to do anything else the whole day! I use a totally organic systemic solution for aphids based on fermented soy oil and herbs, works well against lily beetles too and even spider mites. I pour it on the soil every 4 weeks between March and September. Saves the skin on my fingers :-)

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    1. You seem to have more than your fair share of pests down in London Helene, must be your warm climate. I like the advice that Sooty Mould can be removed by rubbing each leaf with soapy water when I have several infected Rhododendrons at around 10' high :-)

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    2. Yep…similar to the one about aphids, I wonder what size/how many plants these people have who give advice like that…:-)

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  8. I've never heard of this and so will watch out for it, There always seems to be new pests and diseases rt learn about

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    1. Hi Sue, I am getting paranoid about the new killer Aquilegia mildew now!!

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  9. Sooty mould is awful and I think I would despair if it was in such large trees. Would it be possible to buy something that would eat the eggs, like ladybirds? (I know they eat aphids, I don't know if they eat scale insects.)

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  10. To the best of my knowledge there are no biological controls which will work in the open air Sue, so I am afraid systemic insecticides are the only realistic choice.

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  11. I don't grow rhododendrons, but I have had to apply the same solution to diseased Magnolias and Redbuds. Best thing to do is put an end to their misery.

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  12. Luckily with my rhododendrons they will grow back again, although I have found more traces of the pest on camellias and holly seedlings.

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