Not tried it with Roseau, but multiple applications of a strong Round-up mix (from concentrate) during the fall have killed everything I've tried it on, including some pretty tough stuff. Most failures with Round-up are related to several mistakes: 1) Expecting a single application to work. 2) Applying when plant is dormant or in spring 3) Weak mix 4) Getting rained on too soon.
Done properly and repeated over time, Round-up will kill any plant lacking the Round-up ready genes.
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