Answer: This has been a difficult growing season due to the dryness during the summer which followed such a damp spring. The initial spots may have been related to that damp weather which is conducive to a variety of fungal infections, for example. The dry weather was very hard on new plants because they did not have fully established root systems and so were more subject to drought stress than more established plants.
At this point, you need to make sure the plant is well watered so that the soil stays evenly moist like a wrung out sponge until it freezes in late fall. This means damp, not saturated/sopping wet and not dried out.
To know if you need to water, dig into the soil with your finger. Check both the original potting mix and the surrounding soil. If it is still damp do not water yet. When you do water, water slowly and thoroughly so it soaks down to the deepest roots. After watering, wait a few hours and then dig down to see how far it went; sometimes it is surprising. It is better to water deeply less often than to sprinkle lightly every day. Avoid wetting the foliage when you water as this can enoucourage disease problems. Correct watering is the most important thing you can do to help this plant.
Using an organic mulch in a flat layer over the root area also helps keep the soil more evenly moist, it also helps feed the soil slowly as it breaks down over time. Maintain a mulch layer about two to three inches thick year round.
This fall, clean up and remove all of the fallen foliage to limit sources of reinfection with the fungal or bacterial spots next year. You could also top dress with some good quality compost. (It is too late in the season to be fertilizing now.)
Next spring, apply a top dressing of good quality compost as well as a general purpose fertilizer (either granular or slow release) such as 10-10-10 per the label directions. Also water as needed to keep the soil evenly moist next summer. If you see the spots reoccuring next year, consult with your county extension right away to determine how best to treat them.
In the meantime, I would also suggest you consult with your local county extension and/or retailer where the plant was purchased, especially if it has a warranty. Since it has some green leaves it is still alive, although it does not sound very healthy. Nonetheless, it is still quite possible it will overwinter and regrow very nicely next year. Good luck with your shrub!
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