Leaves on various plants are turning white - on some daisies, lemon tree. . . .
Leaves Turning White
Certified GKH Gardening Expert
Not knowing for sure the extent of your problem, I would venture to guess that your plants may be suffering from powdery mildew. The following article should be of some help to you: https://www.gardeningknowhow.com/problems/get-the-cure-for-powdery-mildew.htm