This plant has grown on me. It is one of my favourite Austins. The bloom display is exceptional during the first flush.
This is a very disease free, fragrant rose for Toronto in my no spray garden.
Repeat is not as satisfactory as I would like but I will let the plant settle for a few years and evaluate again.
It has only been 2 years since I had this rose, yet it is already a 4X5 shrub with 50 + buds waiting to bloom. I expect long canes to appear later in the summer as had last year that would be tied up to form a low pillar. TG is extremely hardy. Stem tip dieback only in the crazy winter of 2007-08 in my z6 garden with only burlap as protection.

The description page for this rose says it is susceptible to blackspot. There is nothing about that in the references, and the only member comment that mentions blackspot indicates that this rose has good resistance.

The member ratings (which admittedly must frequently be taken with a pinch of salt) claim excellent resistance to disease, but obviously without any indication of which disease this relates to.

There is one photo (Photo Id: 288945) which appears to show some "blackspot", but based on a recent conversation with Michael Garhart (https://www.helpmefind.com/gardening/l.php?l=21.288890&tab=32) it looks to me as though that spotting may be caused by Cercospora instead. The grey centres in the spots are a trait of Cercospora, and don't appear with Diplocarpon.

So the question here is: where did the "Susceptible to blackspot" warning come from?

Edit: Found this over on houzz (in the "Guillot Generosa Roses" thread) - "I used to live in Thailand (20 years ago) and now I live in southern Mississippi. We have very high heat and humidity here too. I have 5 plants of Martine Guillot and they are some of my healthiest roses. They do not have problems with blackspot or mildew and I rarely spray."

In my zone 7 eastern North Carolina garden my summers are long and hot with high humidity. Every Austin rose I have ever tried contracted overwhelming black-spot. This variety was no different. The flowers are fragrant in cooler temperatures, but lost most of their scent in the heat. In most cases I will not judge a rose for black spot resistance until it has been in the ground in the same spot for at least three years. This allows the pathogen to establish itself in the soil and debris around the rose. Roses that appear resistant during the first two years often begin contracting the fungal disease in the third year. Young Lycidas began showing signs of black-spot almost immediately.

St. Swithin is disease resistant in zone 6B, Kentucky, without spraying fungicide. Very easy care. The blossoms are radiant with a light but sweet scent. Generous bloomer with old fashioned look.