Generally speaking, you're NOT supposed to use weed killer in the same beds as good plants, because rain or watering can start washing it into the soil/roots around the good plants, and sicken or kill them from the ground up. I'd stick to hand-weeding and mulch for weed control IN beds. Or you can get some kind of slow-release fertilizer / weed controller pellets and apply that early in the season. Or at least consider gravity. If you water downhill from good plants you should be relatively okay. But if your plants are on the same level or downhill from the weed killer, there will be problems. Otherwise, your pictures indicate regular heat/sun stress behavior. This is normal, unless you water a little in the evening and the plant still looks like that first thing the next day.

Normally when I see brown in the summer, I suspect a lack of water problem. The first indication of watering issues is browning on the leaf edges, which then 'moves' inwards but you also have some brown lesions in the middle of some leaves... that look resembles leaf spots, a fungal infection that spreads by overhead watering and high humidity areas. As the lesions grow, they can cover large portions of the leaf or all of it. I would proceed by first making sure that the soil is kept well mulched and evenly moist. Then make sure that there is no watering of the leaves. When watering and mulching, remember that the climbing hydrangeas have a large root system so water/mulch a bit far away from the trunk. Water the soil early in the morning, not the leaves. Test the soil in multiple areas before watering (to make sure that water is needed) but also test close and away from the main trunk. That way any root areas that are dry will get some water. Throw away any the worst of the infected leaves in the trash (say those whose = or > 1/3 of surface area is diseased). Monitor what happens and post again if there is a change. Leaf disease info: http://www.aces.edu/pubs/docs/A/ANR-1212/ANR-1212.pdf

I grew a Nkko Blue in total shade not a bit of sun light for 15 yrs. that was as long as I owned the house. It was still there and thriving when I sold the house. This particular plant flowers on old wood and planted against the house in total shade under the roof overhang kept the snow and ice off and it was able to bloom. The evergreen bush planted in front of it protected from the front. Last year just for a test I picked up a Endless summer at Lowes in the markdown area for 3.00 and planted it in my hosta garden that is total shade no direct sun at all and it is blooming although small it only has two blooms but I am hopeful it will do well in the dark. I can say this summer even my full sun plants are not happy with the amount of sun and high temps we have gotten this year. Maybe global warming will make us all re-think what plants really like to be burned to death. So Ken if it was my plant and I was not happy with the blooms I would plant it in the shade and see what happens. It will not die in more shade at the worst thing that will happen is you may get less flowers.

It is most commonly a soil moisture issue/hot temperature issue. The first thing to go when the plant is water stressed are flower buds and flowers. Otherwise, you would see the blooms fade (after a while) and start a color change progression that ends in brown blooms. I already went thru that early browning when my temperatures zoomed to the 100s. Heat dries out the sepals and makes them brown out if the plant cannot provide extra water. The heat can be in the environment or bounced off walls or in rocks that people put as organic mulch. Try giving it more shade (I aim for shade after 11am) so cover it with an umbrella or chair. Also supply more water and see if these things helps. In my also clayish but amended soil, I provide plants with 1.5 gallons of water per bush per watering. Try watering the soil (not the leaves) early in the morning and water from the root ball outwards. Mulch -about 2-3" up to the drip line also helps. Unusual causes: gray mold is a fungal infection of the blooms. The blooms brown out, feel papery and are covered with a gray-ish mold. But it is usually more common in the Spring or Fall.