The plant has been growing nicely and is about four feet high. The flowers have been drying up and the top leaves have been curling. I have seen aphids and have applied an Ortho product for vegetables and flowers. Is there anything else I can do since the insecticide doesn't seem to be making any difference?
Try using neem oil. This is an effective treatment for aphids and as a bonus, it's also an effective fungicide. Here is more information: https://www.gardeningknowhow.com/problems/pests/neem-oil-uses.htm