Usually when a rosebush drops its leaves it is some form of stress or shock. The stress can be strings of very hot, intense rays of the sun days, to not enough water, insect or fungus attacks, etc... Here is a link to an article I wrote on this subject for you: https://www.gardeningknowhow.com/ornamental/flowers/roses/leaves-falling-off-roses.htm
Keep the bush watered well and the foliage should return once the temps cool or the stress is otherwise relieved. I recommend watering the rosebush with some water that has both a good root stimulator and a product called Super Thrive mixed into it. Water the rosebush with a freshly mixed batch the next 4 to 5 times she needs watering, this will help relieve the stresses. Only spray with an insecticide or fungicide if you are sure there is a problem with either one that is causing the problems.