Aphids are a perennial problem in the garden but you do not necessarily have to resort to chemicals to kill them.
There are just as many organic treatments for aphids as there are chemical ones.
Quite rightly so as aphids can cause extensive damage, feeding off plant sap and transferring their various viruses in a dangerous cycle. Roses in particular can really suffer from an attack of green fly or the like.
Before going out to purchase a product it is worthwhile trying out a substance that usually gets thrown out, quite literally down the plug hole.
Soapy water might take a bit longer to get to the route of your plants problems but it is pretty successful against a lot of common bugs.
If nothing else it is basically free and therefore well worth trying before resorting to branded potions.
You can throw the water on the plants just as this method was more than likely discovered many decades ago. However it is much easier to fill a spray bottle, these are very inexpensive and can be easily reused for chores around the house. Once armed with your sprayer you can then tour your plants liberally covering them with harmless soapy water.
There is no risk from over treating them, although over enthusiastic splashing can cause harmless staining of bigger leaved specimens. This can be cleaned up with a damp cloth.
This great alternative to proprietary products is very environmentally friendly and you could even go one step further and use eco soap too.