I had to look up Weedex. It's a weed killer to use on lawns.

So yes, it's selective. Selective for broad-leaf plants such as raspberries & periwinkle!

Ack! That's what I thought! haha

If I was careful not to spray any on their leaves they should be alright?

You can try. Shield the plants with cardboard or the like.

That said, the slightest breeze, or even just the turbulence of the spray, can propel the weedkiller onto the berries & periwinkle.

Sounds a bit risky! :P

It's still early in the year and i've heard of people sprinkling corn gluten meal around their bushes to stop new weed growth. Anyone ever try this? Have any success?

The simplest method of "weed" control is a good mulch that keeps these unwanted plants from getting the sunlight they need to grow. Newspaper, covered with a mulch material to hide it and hold it in place, helps extend how much mulch you need to use. Mulches will aid in suppressing unwanted plant ("weed") growth, aid in conserving soil moisture, aid in controlling soil temperature, and (if the right stuff is chosen) will add organic matter to the soil something almost all soils need.

Thanks for the help folks!