still waiting a reply thank you

Hi Jonb and welcome to GoY, we are a bunch of amateur and professional gardeners not some sort of panel sitting waiting for questions to come in so you won't get instant replies. Simple answer to your question is no, not unless you want to run the risk of getting round up on your Pieris and killing it, you'll need to dig them out.

Well you can - but you must do it on a still, windless day, and you must cover any nearby plants (including the Pieris) so that none of the spray makes contact with them. The weeds you spray should be growing strongly, and the ground should be damp.

Even if you have a still, windless day, as Bamboo advises, still be very careful when you spray. I sprayed weed killer recently on some weeds and still managed to get it on some nearby plants that I didn't cover up. I'd rather just pull the weeds up.

It is safer to use the dilution recommended for watering cans. That way you don't get spray drift. But unless your weeds are very deep rooted its is better to pull them out if you can. And if you have to use it use simple glyphosate rather than Roundup which has more additives that stay around in the soil afterwards.