Powdery Mildew

If a lot of plants have mildew, I would suggest just refunding the customer but telling them that fungal issues aren’t in the plant – they are on the plant, and so once the foliage drops, it no longer has the problem. Even better if they can discard all the fallen foliage. Furthermore, as ubiquitous as it is, powdery mildew strains are genus-specific, so just because a honeysuckle has it, doesn’t mean it will spread to neighboring plants (unless they are also honeysuckles).