How to look after Rhododendron plants?

[Ngnra]

I have a few rhododendron plants in my garden, some of them had been attacked by fungus last year.

I sprayed copper solution a few times at regular intervals. 
Would like you to see it in the uploaded photo and advice if the plant is disease free.

I can see some buds on it, don’t know if they are flower buds or leaf buds.  The flowers in the photo below are tulip bulbs.

RhododendronRhododendron

[MitchellMc]

Hi @Ngnra,

The white speckling on the leaves is likely a fungal infection called powdery mildew. Is this the fungus you were treating last year? If this is a new issue, then it looks like you'll need to hit it again with the copper-based fungicide. While you're at it, remove and dispose of any leaf litter at the base of the plant, as that's often where these fungal attacks arise from.

Let me mention a few of our knowledgeable members, @Noelle, @Adam_W and @BradN, to get their thoughts.

Mitchell

[Noelle]

Hi @Ngnra and @MitchellMc 

Silvering of the leaves of azaleas and rhododendrons  can sometimes also be caused by mites, which suck sap from the undersides of the leaves causing bleaching on the upper surface. This could be the cause of the whitish appearance.

If it wipes off on your fingers then it is likely to be a fungal problem; if it stays in place then check the undersides of the leaves for microscopic pests.

Usually a systemic insecticide (one that is absorbed into the foliage and circulates through the sap system) is the most effective control for pests like mites. However, you may have problems finding one for home garden use. If so, then a general insecticide like pyrethrum sprayed on to the pests on the underneath of leaves may be effective.

[MitchellMc]

I apologise, @Ngnra. @Noelle is correct; it's much more likely to be mites now that I look at it again. That's why you call in the horticultural experts! 

Mitchell

[Ngnra]

Thanks for your reply; I have Yates’s Conqueror which I bought a few years ago. Can I use it to spray the rhododendrons?

[Noelle · Accepted solution]

Hi @Ngnra 

The product you have should do a reasonable job on the mites affecting your rhododendron.  It is essential that, when applying it, you thoroughly wet both upper and undersides of leaves, as these pests may be found on either.