Rhododendrons: Rhodo leaves yellowing/browing

Hello,

I'm very new to outdoor gardening and don't know much about rhodos. I have three in our front north facing (shady) bed. They are fairly small and about 4 years old. The last 3 years, they have produced a few yellow flowers per plant.

This year, only one of them flowered, and produced only one flower clump. When it died, I dead headed it (first time I've done that in 4 years). I have also noticed that in the past week or so, some of the leaves are starting to turn yellow and brown (the plants were previously looking good, and growing new leaves everywhere).

Can someone help me with identifying why the leaves are yellowing/browning; is this normal? Is it due to neglect (since I haven't done much with these plants)? And what, if anything, can I do about it? Thanks so much!

 

Looks like mildew. This is common here now. To keep it off you have to spray fungicides perhaps several times per year. I avoid the issue by no longer planting varieties prone to conspicuous damage (susceptibility varies, same as with roses, orchard fruit trees and flowering crabapples).

 

Hi, Not sure if it's powdery mildew, but a picture of the affected leaves undersides may be interesting. Wondering if it may be normal for a plant that has suffered a little stress, some rhodos drop some of their one year old leaves as new leaves develop. Some of the yellows, probably most large leaved ones grown locally, need particularly good drainage. As far as flowering, it may not normally bloom at a young age and may need 6-7 years to bloom consistently. In the nurseries bloom promoters can be used to force them to bloom younger. One called 'Hotei' , which your plant resembles and may be , takes some years to bloom properly. Other than the few poor looking one year old leaves, would think your plants look pretty healthy. Seems the leaves most exposed to sunlight are the most seriously affected. Other members may have more experiences or suggestions.

 

Blotching and premature dropping visible in these shots typical of mildew.

 

Thanks so much for your replies. The mildew certainly makes sense, seeing as it's been such a wet spring/early summer so far.

 

Actually I think it would come on at this time at least partly because mildews generally are associated with drier conditions in summer, there may even be a greater incidence on specimens that are drought-stressed. If the leaf surface has been dampened (Pacific coastal areas may have much fog and dew in summer, while soils are quite dry) it may make conditions optimal for some mildews. Washing of the foliage by rains or hosing on the other hand can make it harder for them to get started or develop fully.

Also summer is typically when broad-leaved evergreens discard old leaves. What is different with mildew is that these leaves become old before their time, producing a gaunt appearance to the shrub or even death.

 

That's very interesting! I had assumed that more moisture (like the rain we've had recently) = mildew. Thanks for the info.

 

More moisture up to a point. Many need damp leaves but are inhibited by water moving over the leaf. The fact that some kinds of mildew spores travel with their own little packet of moisture shows how much mildews infesting plant parts is a dry season phenomenon.

For the details of rhododendron mildew specifically there are web pages up that talk about this, surfing "rhododendron diseases" as well as "mildew" may help bring up pertinent hits.

Rhododendron mildew is so pervasive here and so virulent on the most susceptible varieties that I would expect to see it regardless of variations in weather.

 

What if,

You fed it Rhod special food? You should always feed them the correct feed which that did remove the dropping of yellow leaves for me along with ericacious compost twice this summer. There is a deficiency rhodies suffer from called chlorosis which produces the yellowing and the special food seems to work as I have no droppping or yellow leaves as yet...touch wood.

Mine did'nt fair to well last year mainly due to a normal compost but this year I expect it to be flowering better as I bought ericacious compost twice this year.

Rhodies here flower in their first year. I bought a new one (dwarf) so in the spring all being well I will bring in a pic when its in flower.

The image is my older dwarf Rhodie and as you can see most of the yellowing is gone, it will get a couple of feeds through the winter...it was a mess with sparse flowering this easter.

Two links:

http://www.treesforyou.org/Planting/TreeCare/Healthy/yellowl.htm

http://www.glendoick.com/content.php?page=advice

The new image is Rhododendren Shamrock, its one I bought this year, its a dwarf.