Rhododendrons: Rhodo diagnosis needed

The following was received via email:

I'm hoping you can help me, or point me in the direction of someone who can help me, identify the nature of the malady that has affected two of our Rhodos. We recently moved into a house whose garden had been neglected for many years, so we're trying to spruce it up and revive the ill plants.

I've attached a couple photos that clearly illustrate the symptoms, which include yellowing of the leaves, leaf spots that look amazingly like severe rust on a car fender, and occasional flower buds that have turned brown and became covered with short black powdery hair. I don't know whether this is caused by disease, bugs, fungi, poor growing conditions, or a symbiotic combination thereof.

We appreciate any assistance you can offer. Thank you very much in advance.

 

The second image:

 

Douglas Justice replied:

Thanks for the pictures. It looks very much like both rhododendrons are suffering from a lack of fertility. The yellowish leaves point to that or to too much sun exposure. Rhododendrons are almost always happiest with some overhead protection, like that provided by tall conifers. Full sun all day is very hard on the leaf tissues, particularly if summer irrigation is inadequate.

It looks like you have "bud blast" on the first picture. This is a problem on some rhododendrons in some years. Locally, it seems to be only a minor problem. I suspect that most of the time, it results from stress (drought, heat, infertility, etc.) killing the bud from the inside -- a sort of self pruning. Once there is dead tissue, it inevitably becomes infected with one or more generalist fungal saprophytes (saprophytes live off of dead tissues). The fruiting structures of some kinds of fungi produce that odd black hairy stuff on the outside of the bud.

The symptoms shown on the second picture look more like physical injury than anything else. While a number of pathogens can affect rhododendron foliage, these are usually only present where conditions are perfect for the pathogens and terrible for rhododendrons.

 

Bud blast can also be caused by sun; however I don't see sunscald on the leaves. There is not enough to tell from the pictures but leaves are not right. This looks more like nutrients -- feed it miriricle grow, holly food, and perhaps a dose of Iron but Rhodies don't need much fertalization and never fertilize past about july. If you are revitalizing, did you lime the grass? Lime will cause yellowing and even kill the plant because they are acid living plants (check soil Ph). The first thing I think of when I see leaves like that is a Ph. problem.

 

Rhododendron bud blast is fairly straightforward, you can probably figure out if you have that. What else may be going on is far from obvious.

Sample your soil and have it tested if a nutrient deficiency is suspected.

Fall fertilization is more effective than spring, due to both the environmental conditions at the time and the condition of the plant. Dolomitic limestone can produce an improvement in the condition of a rhododendron if it supplies something that is deficient (such as magnesium, in this case), same as with any other plant.

 

Maybe I'm just old school but I have had it grilled into me that lime and rhodies is an absolute no-no because of PH and that maintaining PH at 4.5-5 cures most rhody chlorosis problems not caused from kids and pets. But I'm not too old to be unschooled (I don't think). So would like to hear more discussion on lime use and rhodies...

 

Hi

Check out things ( I found most predominate in your area)

1 check that there is no plastic used as a weed barrier.

Give them a shot of epsons salt at @2tbl/gallon on and around the drip zone /and spray them with an anti bacterial soap ( mild mixture)

with the changing enviroment it is not that uncommon that rhodies will try to bloom 2 to 3 times a year if the last bloom starts when the blight rain hits that the developing buds will turn to mush.

Before moving North the gated comunity in Abbostford that we looked after had 1200 rhodies we lost 4 in 5 years.

Regards Doug

 

I agree with Doug's recipe of epsom salts and soap spray. Also, provide morning drink of water when not rainy (morning fog simulation)