Certified GKH Gardening Expert
Leaf scorch is usually due to going through a period of high temperatures or reflected sunlight hitting the leaves. The rosebushes simply cannot move enough fluid to the extreme outer portions of the leaves to keep them from burning up during times of high temps outside. Keep the roses watered and things should improve once cooler weather sets in. If your rosebushes are planted where they get total sun and heat contact for much of the day, this is likely the problem. One way to avoid the leaf burn is to erect something that will give the roses some shade for part of the day during the hotter times.
Another possibility is when water or pesticide sprays have been allowed to pool on the leaf edges during the hotter times of the day. The water or sprays remaining on the leaves acts like a magnifying glass and burns the foliage with the sun's rays.
https://www.gardeningknowhow.com/ornamental/flowers/roses/brown-edges-on-rose-leaves.htm
This looks like a fungal infection although it may be superimposed on leaf edges that browned due to drought or extreme heat. If the entire plant is affected then use a systemic fungicide from a garden center. There are DIY formulations that are best left to preventing, not curing a fungal problem. More information is here: https://www.gardeningknowhow.com/ornamental/flowers/roses/brown-edges-on-rose-leaves.htm
