Thanks, Henry. Re your comments - perhaps the red coloring shows up on roses that normally have red new growth.

Jackie

Henry, the statement about thick red growth by the Marin Master Rosarian appears to refer to herbicides in general rather than RoundUp particularly. Overgrowth symptoms resembling RRD might be caused by 2,4D and similar chemicals.

The Oklahoma State fact sheet on RRD says,"However, excessive thorniness and unusual red pigmentation does not usually occur with glyphosate." Generally, glyphosate injury on other plants causes stunting and yellowing rather than overgrowth.

This is not the last word on the subject, but I would like to see a science-based source indicating that glyphosate causes overgrowth and redness in some roses (or any plants). I guess it's possible that a light dose causes opposite symptoms from a heavy dose.

To further complicate the situation, many men are colorblind.
That deep reddish color that some of us associate with RRD-caused growth....well, my husband is colorblind and he doesn't see that as red at all, just a slightly different green.
And, FWIW, he doesn't see it on a roses from a number of different classes; nor does he see it in photographs (when many, many in audiences do see it.)

Isn't Marin in California?