Could this have been in contact with herbicide?

I'd just cut out the affected branch.

You're right, gardengal48! I misspoke. In my head I was thinking it might be a disease, fungus, or insect - and presumed spraying with the appropriate remedy. In the meantime - this is precisely why I am posting my question here - to find out what this might be.

I'll have to think back to if I've used any herbicide recently there. I didn't think I did, but perhaps so. You seem pretty confident it is herbicide damage so I must have inadvertently got it!?

Thanks much

Is it at all possible that is some other plant that is growing up into your Weigela?

There appear to be branches showing both types of foliage. I believe it's all Weigela..