Since it is mostly lower or older leaves, I would guess it is normal senescence. This is very common at this time of year here due to our very dry summers. Lack of adequate irrigation can accelerate it.

Thanks, who would know! the seeds I put in the feed did include a lot sunflower seeds, will move the feeder to a different location. Thank you so much!

While the allelopathic effect of sunflowers is well known with association of other crop-type plants and weeds and grasses, I know of no studies showing it has any affect on established woody plants, like rhododendrons or other shrubs. Typically, the allelopathic effect is restricted to seed germination or seedling development.

I would be very surprised if the sunflowers were causing the yellow foliage. In fact, this is a very common late season phenomenon on rhodies in our area that have never been close to any sunflowers!!

@gardengal48 - what worries me is that I did not see this last year, and due to its location ( planted under a mature vine maple), it would be very hard to replace. So I want to keep it as healthy as possible.

How have you tended the plant? Does it get any supplemental irrigation?

Other than being off color, I see nothing obviously wrong with the plant - the new growth is a good color and there are even buds formed. There are no obvious symptoms of disease or insect issues, although a closer exam might turn up a few minor issues. But it is not always easy to be accurate in any plant problem diagnosis just by looking at a couple of photos :-) If you continue to have concerns, you might want to take samples of the yellow leaves and the photos into a better local nursery for diagnosis (if yours offers such a service - many here do) or to your county extension office.

I will say that there are a dozen or so large, very well established rhodies on my property that go through a similar process of lower/older leaves yellowing and then dropping starting around the beginning of August. Some get watered routinely in summer; some do not, depending on how far away they are from the house. And how big they are. But they all do this to some degree or another in late summer.

@gardengal48 - a month ago I was preparing staining our deck, after pressure washed it I had to turn off sprinkler system due to how the zones are set up. so there were 2-3 weeks time the plants didn't get watered in regular basis (used to be every other day), but since it's in the shades and fairly mature, I was thinking the sprinkler was more for the perennials in the bed, and they seemed to be fine.

Just to clarify, I wasn’t suggesting that the bird seed caused this yellowing after a month or two. But based on personal observations in my garden, the perennial plants that regularly had sunflower hulls rained down on them didn’t do as well as those that didn’t back when I had bird feeders (feeders are no longer possible due to black bears living nearby). So if it were mine, I would move the feeder as a preventative measure on the basis of my observations and the philosophy of better safe than sorry. I don’t know that it will interfere with the rhodies, but since I cannot be sure that it won’t, I would rather be cautious.

Compared to most of my rhodies, this seems to have more yellow, though mine do have some leaves that change color and drop every year, but I most likely have different species/hybrids and live in a different part of the country, so behavior here may be different. Since the watering was different this season than last, I would check soil moisture by actually feeling the soil a couple of inches down. With rhodies you don’t want it either too wet or too dry.