I've got a honeysuckle in a trough. Growing really well. Have noticed that some leaves have a kind of grey colour appearing on them. Any ideas? Could it be mildew?

The trough is in a very sunny spot and I have been keeping it very well watered ... maybe over-watered? Would that cause this problem?

I don't want to loose the plant as it is hiding an ugly wall.

Any help appreciated.

Thanks.