Marco Banks wrote:
All those aphids are going to invite ladybugs, spiders and all sorts of other beneficial insects to your yard. The radishes look like they are going to seed very nicely, so even if you want to capture seed for next year, the aphids are not really hurting anything. In fact, they may be sacrificial plants that keep the aphids off of other stuff.
I'd say let nature take its course and see if you get a host of predator insects coming in to feast.
I did a quick Google search of plants that attract ladybugs:
By the time you planted those plants and they grew to maturity, your radishes will be long gone --- but for future reference, you may want to plant a mix of plants that will attract and keep the ladybugs in your garden.