Can you get a soil pH kit from a plant nursery? Perhaps one with numeric readings as opposed to some cheap ones that give results by changing the color of a water based solution? Use it to check if your soil is either acidic (pH below 7.0), neutral (pH of 7.0) or alkaline (pH above 7.0). I suspect your soil is very alkaline, with reading much above 7.0. Hydrangeas have difficulty absorbing nutrients at those levels, which results in interveinal leaf yellowing. If not corrected, the leaves can brown out. This can also caused loss of vigor and stunted growth. Normally, you counteract the alkalinity by amending the soil with either garden sulfur, aluminum sulfate or iron-chelated liquid compounds from a plant nursery and apply the product per label directions. In the meantime, ensure that the plant still gets morning only sun and that the soil is always damp/moist during these hot summer months.

Those are tiny little things!! When were they planted and how big were they then? And where are you located?

That doesn't look like any disease. So cut out the spraying :-) It could be climate, it could be size, it could be some delayed transplant shock, it could be lack of water. The last is probably at the top of my list.

These were planted around march 14, both rather small. One was dormant the other had been under lights inside for about a month and a half, since it was shipped to me during the winter. The one under lights was maybe 9", the dormant one maybe 3" or 4"? the indoor one actually started showing symptoms while indoors, the dormant one was initially healthy, but seemed to "catch" whatever this is from the other once they were both planted out. The first one to show signs has nrarly defoliated twice but comes back with the same weird stunted looking growth. They're about 8'-9' apart I think, I'd have to measure to be sure. I also have an invincibelle 2, a smooth hydrangea and a limelight planted the same time, in the same area, but although 2 had issues of their own (limelight lost all it's foliage on being planted out, I might not have hardened it off long enough, and something kept eating my invincibelle until I put a cage around it) they've recovered are doing fine although still small, and only the two macrophyllas seem affected by whatever this is.

I am not sure what the ph of that soil is exactly, but we had it tested last year and it came back slightly acidic, somewhat nutrient deficient (we added fertilizer in the recommended amounts) and extremely high in zinc, much like the rest of our yard. I don't think it can be lack of water causing this, they've been on drip irrigation since day 1 and have gotten a deep watering once a week (unless there was a lot of rain) spring, and now at least twice weekly. The soil isn't swampy, it drains ok but I haven't let it get home dry either, water has been regular. Sunlight is morning only, then they're in shade for the afternoon and evening. I see a lot of hydrangeas doing well under trees and against houses around here, so I don't think that's too much shade but I could be wrong. I did give them a quick spray of permethrin each time when I started my yearly battle against squash borers in may, just in case it was some kind of insect damage, but that did nothing so I stopped. I'm located in Arkansas, zone 7.

I hope that provides some more clues? Thank you for your help!

"extremely high in zinc,"

How high is extremely high? Some plants can be very sensitive to zinc toxicity and they will produce symptoms similar to what your plants are showing - stunted growth, cupped or curled foliage, drying and browning of leaf tips and chlorosis.

If macrophylla hydrangea are zinc sensitive, then that would make sense! I can't find my file for that exact spot, but here is the next closest, zinc was like this all over our property when tested. We did add some lime the year before to try to counteract, and since the soil was even more acidic before that.

This is last year's test, we haven't tested again this year yet after amending.

I'm fairly new to gardening in general, this is year 3 for me, so please forgive me if I've missed something obvious!

Zinc toxicity can account for ALL the symptoms showing, not just chlorosis. And with tested high levels, that is far more likely to be the cause of the hydrangea issues than alternaria, which is not all that common. And there is no sign of the of the haloed spotting on any of the leaves, which would indicate alternaria or other fungal leaf spot. I seriously doubt this has anything to do with a fungal problem.

Did the providers of your soil test not give you any guidance on how to mitigate the high zinc levels? The typical recommendation is an application of phosphorus but P levels are already on the high end and it will also serve to raise pH as well.

I'd get back to the soil lab and ask how to remediate

Thanks! My extension office seems overloaded right now, I still haven't received a reply about several disease issues I had earlier this spring, so it might be a while before they can look at it. I might try that later though if this is still an issue. If it is Alternaria, what fungicide would you recommend?

The only guidance we could really get about the zinc was to add lime to at least move our soil toward a more neutral range. That came from our extension office.

Until you get a confirmed diagnosis, do not apply any fungicide! It is probably unnecessary, may actually be harmful and there is no sign of any sort of spotting or fungal disorder on the newer growth and the older, browned leaves cannot be 'regreened' :-))

Ok, so it looks like I need to see if there's anything else I can do to address the zinc issue first, then maybe look at fungicides if that doesn't help. Thank you!