This looks like the dotty, yellow ('stippling') damage done by tiny sucking insects called mites. 
If you were to take a hand lens/magnifier and look at the back of the leaves like the one in your first photo, you will probably see them, or you can look at a similar photo on our page about them here: 
https://extension.umd.edu/resource/spider-mites-flowers-and-groundcovers

You can lessen their impact by aiming a strong
 water stream from a hose on the plants, aiming at the back of the leaves. The worst yellow or browning leaves can be removed and put in the trash. More approaches are in the link above if needed.


Christine