Petunias can be an Aphid magnet, but they are quite easily dispatched with just a strong stream of water to knock them off the plant. No need for very strong, broad spectrum poisons (Sevin) that will also kill off any beneficials that could help control those Aphids.

where could I buy this? in Canada

I agree with you,my white Petunias are turning brow, all I used was No Bug.Help somebody and help me get rid of these pests.

The simplest means of Aphid control is a sharp spray of water to knock the wee buggers off the plants. Those knocked off the plants do not return but since Aphids are very productive you will see the next generation. Spraying any insecticide, Insecticidal Soap, Neem Oil, pyrethrins, etc. will not only kill the Aphids but also can kill the predators of Aphids. No Bugs contains Deltamethrin, a pyrethroid or a synthetic pyrethrin.

Perhaps this article may be of some help understanding Aphids and their control.

http://ipm.ucanr.edu/PMG/PESTNOTES/pn7404.html

kimmq is kimmsr

by this time of year.. many Ps are ready to be cut back ...

sometimes its simpler to give it a good cut back.. and remove 90% of the problem.. since they are usually out on the soft new growth ...

and then spray down the remainder with water ... like a quart water bottle.. be a bit aggressive ..

ken