It will likely work, but you will need to recut the stems and apply immediately. Follow the directions for cut stem applications. Good luck.

RoundUp is absorbed into photosynthesizing tissue. This means green stems, too. Even stems that don't 'look' green to us may likely be likely candidates for RoundUp absorption. You don't really need to re-cut the stems (but you could).

RoundUp can also be pretty easily absorbed by young trees and shrubs, as well. It's a bit of a misconception that this chemical will not be harmful is sprayed on woody trunks. Be careful when spraying the grass from the mulch ring around a newly planted tree. It will probably not kill the plant, but can cause significant damage.

Roundup is not only absorbed through leaves and green stems, but can also enter a weed through cut stems. It is essential that these stems be freshly cut, however, to facilitate the movement into the plant. Old cuts will not allow the material to move into the plant appreciably.

Roundup overspray on bark that is very thin, green or cracked may affect the plant, but thicker woody bark is an effective barrier to Roundup.

Do you use eye droppers for that application?