Posted: 26/09/2016 at 21:12
yes, as others have said, this is mildew.
to avoid next year ensure plants do not dry out. In spring water well then apply a generous mulch.
Ideally, dig up and add plenty of compost to planting mix and replant
should this...mildew...occur next summer cut back all foliage, tidy away debris, mulch and water well and this should keep mildew at bay