I have lots of aggies spread about my garden, generally in places where
water is scarse (there are lots of those). It seems that at the end of most
summers they get a bug which deforms the leaves and gives a white powdery
look in the centre of the plants. They seem to recover of their own accord
though I would like to give them a helping hand if I could work out what is
wrong with them.

Any clues?

Jflooz