Eh, I think the stronger the plant, the better it can thwart those things. I would think vigor would be more important than OR vs grafted. But I'm no expert on the subject.

I would tend to agree with Brittie. Also, I think it has more to do with a variety's susceptibility than whether it's grafted or own root, that's from my own observation and experience. I'm no expert either.

I'm with Brittie and Sara-Ann. I have Soroptimist International OR and grafted, both one year apart in age (5+ years) and both plants exhibit the same level of blackspot.

The only way I can see this being true is this way:

Say Dr. Huey doesn't perform well in your part of the woods (aka, South Florida) but a certain rose does well on its own roots. Then that rose would show more vigor and strength on its own roots (hence that being a particular case she/he may have encountered).

However if a rose does not perform well on its own roots, then it will forever be more susceptible to diseases and pathogens, etc. when being grown on its own roots, but may perform admirably grafted.

It all has to do with the TYPE of rose and the TYPE of root stock.

The only other way I see this being true is if the graft is somewhat weak or faulty resulting in a bad performing rose.

Some roses do well on their own roots others do better grafted and in some cases Dr. Huey doesn't do well and own roots perform better, hence she/he may come to the conclusion that own roots are more disease resistant. In my garden Dr. H performs miserably. Many roses do better on their own roots but all do even better when grafted on to Fortuniana.

thanks for affirming what I thought. I have Chicago Peace as OR and grafted, both 2 years old and they defoliate at the same rate. If I hadn't been a guest at the meeting I'd have asked for supportive information.