Are you able to share photos of the symptoms? It may be powdery mildew, a very common fungal infection which usually causes no serious or long-term damage to the plants it infects. While some fungicides can suppress it (they cannot cure existing infections, only protect uninfected growth), their use is generally  not recommended, in part because they risk causing harm to other organisms exposed to the fungicide residues. Additionally, they don't always work well, especially since they need to be applied several times over the course of the season to remain effective, require a very thorough application so all foliage is coated during each treatment, and ideally should begin use before symptoms manifest or become extensive. If infected leaves are shed early due to drought stress or heavy mildew outbreaks, then they can be raked-up and disposed of to reduce the risk of re-infection going forward (from the spores they can harbor), though it's not a foolproof measure and if they blow away before you can remove them, it's not a big deal.

Miri