Posted: 21/07/2014 at 10:03
I've copied this for you from the Eagle website:
"This is the white powder that is seen on the plants (see photo at right). This can be kept at bay by spraying the plants with a product called 'Systhane' which is available from most good garden centres. We spray in anticipation from early June, and continue once a month for the rest of the flowering season. Dry conditions and lack of air circulation (plants too close together) can cause this problem. Dry conditions can be sorted by watering the foliage regularly."
.....prolly a little late for this year, but worth remembering for future years.