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Please help ID pest / problem with rhododendron :)

ross_6161ross_6161 Posts: 3
in Problem solving

Hi

We have a rhododendron which seems to have either picked up some hitch-hikers, a disease, or both. Can anyone help identify the culprits from the pictures?

Some of the stalks have black spots, some of which look like insects, others more just spots, perhaps droppings? Some of the top leaves have what look like white insects, but they don't move and are stuck to them (skin shedding?). Some of the leaves have turned brown. A few of the new flower buds look a little brown too. Is this potentially aphids, and if so would they cause the leaf browning?

We treated it with Bug Clear Ultra at first assuming it was whitefly and blackfly, but the numbers seem to have increased. Would be good to identify the offender so we can choose the right treatment!

(backup link to pics https://imgur.com/a/iFOtiV0)

Cheers


Posts

  • coccinellacoccinella Posts: 1,428
    Black aphids and whitefly, but the damage on the leaf seems more like a fungus to me.  It is possible that the fungus is weakening the plant so more easily attacked by pests. Are you watering regularly?  You could try spraying it with garlic and soapy water and remove the affected leaves. Hopefully someone with more experience will come along. 

    Luxembourg
  • FairygirlFairygirl Posts: 55,117
    How big is it and how big is the pot?  A pic from further away would help. What type of growing medium is it in, and has it been refreshed each year?
    They aren't great as pot specimens long term unfortunately, unless you're very careful and have the right sort of climate. The prefer cooler, shadier spots, especially in pots to prevent moisture loss and foliage getting affected by hot sun. In the ground they can cope much better. 
    They also need thorough watering - even more important in pots - as they're shallow rooted. If watering is done lightly, it encourages those shallow roots to stay even nearer the surface, which only makes it worse. 
    Aphids are what's there, and the white is just the shed skin. Aphids will rarely do any long term damage to them, but you can hose them off for now. It's quite unusual for them to attract a lot of aphids. They can get spider mites but that doesn't look like that either. 
    I think the damaged leaves just need removing - I've never seen that on  a rhodo, and they're generally quite pest free - vine weevils can nibble, and they can get honey fungus, but that's not what's there.  Damage from lace bug is also different. However,  if the shrub is short of water, and becomes stressed, it also becomes more susceptible to viruses and pests. There seems to be a lot of weeds in with it which should be removed too. It looks a bit chlorotic in one of the photos, so it could be that it's short of the right nutrients too. 
    It's a place where beautiful isn't enough of a word....



    I live in west central Scotland - not where that photo is...
  • ross_6161ross_6161 Posts: 3
    Hi guys

    Thanks all for the responses! Its actually someone else's plant so I just got the original photos. We went with the assumption that its aphids and treated with the insecticide.

    A large portion of the root ball had actually become exposed due to soil shrinkage in the pot, so we added some extra ericaceous soil and fed with a rhodie feed. Will see how it gets on!

    :)
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