ground elder

dig out as many pips as possible, every time you see them and then in late summer spray them with a systemic herbicide like roundup. this may need several applications. but it will work. i cleared a big border this way.
good luck

Treat with any weedkiller containing glyphosphate (I think Roundup might, not sure). You'll have to be rigorous and probably will need to treat 3 or 4 times before it's all gone. Don't bother to spray if there's been no rain for ages - plants need to be in active growth for any weedkiller to work. And I wouldn't dig them out at all - it's impossible to get the roots out and you need the green topgrowth for the weedkiller to work.

i did dig out a lot of the ground elder as it has a swollen underground structure, possible a rhizome. one of my borders was totally cleared of the plants i wanted first, then i dug it over twice, a month apart and now 6yrs on it is still clear. the systemics are absorped through the leaf surface and then its translocated to the root system. any moisture in the plant is enough to allow active action of the weedkiller. round up does indeed contain glycophosphate but as all the best adverts says 'there are other weedkillers available' :o)