Im not trying to flame you, but the reason that you have an aphid infestation
is that you were indicriminantly spraying your flowers every few weeks.
Spraying only works when there is a pest present. You cannot prevent insects.
By spraying over and over, the few aphids that do survive pass thier genetic
information on to thier young, who then are also resistant. This happens fast
because aphids reproduce incredibly fast. I give this info to my customers on
a daily basis: do not spray an insecticide unless you SEE insects and there
are enough of them to make an impact on the plant. As for japanese beetles, I
pick a few off as I walk by my plants on the way to work in the morning. Im
not pushing organic gardening here, im urging common sense! Horticultural oil
works very good on aphids.

Toad