Convolvulus arvensis...probably would be highly valued if it was difficult to grow...related to Morning Glory.... anyway heres what they recommend...

isolate the thing by giving bamboo cane support then wait until it has begun to produce flowers then give the herbicide...the idea is that its inner resourses will be at their lowest at the onset of flower production...late evening application is worth a try...effects of herbicide can be better .

if its under the fence and that side aint gettin treated....hmm...dunno .