Yes you can - use organic liquid if you have some. I have never worried much about the proportions - more or less doesn't seem to hurt.You don't need very much. I believe all the detergent is for is to lower the surface tension of the water so it can actually touch the little aphids or whatever and presumably drown them. Its probably greenfly on the roses, and they usually cluster round the flower buds. If you aren't squeamish its easy to just run your fingers up the buds and squish them by hand.

Thankyou so much Gwen