Problem with knockout roses
I have been asked for advice on a problem with knockout roses. They were installed a couple of years ago, and grew a lot last year, and were full of blooms. There is mulch around them, and although it was very hot/dry the past few days, I checked the soil a couple of inches down and it is moist. Most of the leaves are green, except for a section, as shown in the picture. The problem seems to be starting at the blossoms and spreading from there. The only creature I found on the plant was the spider, in the attached picture. No beetles...which are pestering a Crape Myrtle close by. The owner has recently fertilized the knockout roses. Is this maybe Botrytis Blight from the cool rainy weather we had last month? Please let me know what you think, and advise on how to proceed.
These are normal spent blooms, not botrytis. The first flush of blooms is usually heavy and when it fades and withers can be noticeable. While rainfall will wash them away or they will naturally fall off, if an owner doesn't want to wait, they can prune off the old bloom clusters. Later bloom will be lighter.
The spider is not affecting the rose at all. Spiders do not eat plants, only insects. They are beneficial additions to the garden because the eat pest insects.