Findings this year

I asked some questions earlier in the summer regarding certain roses. I just want to pass on what I have learned so that others don’t waste their time with some of these roses. I focus primarily on disease resistance, so here are my findings on some roses that were promising. I live in PA.

The climbing rose Winner’s Circle is NOT disease free. It suffers badly from leaf spot.

Rainbow Sorbet is moderately resistant to blackspot (better than most, but definitely not “remarkably resistant to disease” as the advertisements say.

Sadly, Autumn Sunset/Westerland’s blackspot resistance has broken down in this area. Both used to be blackspot free.

Julia Child and Love And Peace are quite blackspot prone.

The one rose that has turned out to be better than expected is Mother Of Pearl. It is blackspot free and exceptionally vigorous. We’ll find out in the spring if it passes on those traits.

Hopefully I have better luck picking them next year!


I love these kinds of reports Shane. Disease pressure must be fierce where you are.

My experience with Julia Child is same as yours.

Strangely, a couple of its seedlings have been completely healthy: JC x carefree sunshine, and JC x sunsprite.

Shane, thanks for the reports - very helpful!

Jim Sproul

Shane, We have a horrible time with BS here, too. I have seen the same resistance as you with Rainbow Sorbet this year, but Julia Child is doing the same as, if not better, than RS while Black Cherry right next to JC is almost nekked:(

Are you talking about Love and Peace the mini? Mine is BS free right now.

Some of my other BS free roses are:

All my Gallica’s


Tahitian Sunset

Out of Yesteryear




Splish Splash


Hannah Gordon

Morden Sunrise

Alexander McKenzie

Golden Buddha


Honey Perfume

First Impression

Honey Perfume

Halo Sunrise

Julie Link

Baby Love


Some of my roses have only some BS around the bottom (like Julia Child and Rainbow Sorbet) but are fully foliated and look pretty good right now. If anyone is interested I can list those, too. I went out a couple of days ago and did an inspection and rated the roses with Very Little BS, A Little, None (quite scientific, I know :slight_smile:. The bad ones I just didn’t write down.

Wow, some surprises in that list. I would have thought at least a few of these were blackspot magnets. I’ve read differing reports.

Very interesting reports. They help point out how important races are and more thorough testing and emphasis on strong horizontal/field resistance. Vance Whitaker for his Ph.D. looked at combining ability for horizontal resistance among a group of diploid parents crossed together and tetraploids crossed together. The manuscipt will hopefully come out soon. It seems like the data supports basically a simple multigenic / quantitative inheritance which is good, but means it will take us some time to increase that level of resistance and when we cross our roses with good horizontal (i.e. partial) resistance with more susceptible roses for color or whatever else we want we water down that resistance.

In some of the race specific resistance screening, we learned most of the Explorers were susceptible to Vance’s race C as well as the HT ‘Love and Peace’. Other roses were resistant/susceptible in different patterns to the other races. It is just so quick to look at a beautiful healthy looking rose and say its resistant. That strong resistance (immunity) holds up until a race comes in contact with it and overtakes it. Generations of dedicated work by Bill Radler led to accumulating more and more genes each contributing some towards partial resistance until ‘Knock Out’ came about. It has some race specific resistance, but then a strong underlying horizontal resistance when the race specific resistance is broken down. This collection of races building and being well perserved at the U of MN are a super valuable tool to screen roses with to help identify their type of resistance and better predict which will hold up to black spot more readily out in the general landscape across multiple races. Roses that have better stood the test of time like ‘New Dawn’, ‘Carefree Beauty’, and ‘The Fairy’ get black spot, but have relatively strong horizontal resistance in that they typically hold back the disease from developing too fast and quickly defoliating the plant. It would be nice to have more roses like that or like Knock Out with some race specific resistance, but then strong underlying horizontal resistance when the race specific resistance (typically a single gene governing it, so it can be taken down easier by the pathogen) is broken down.

For Earth-Kind we challenged the Southern winning roses and mid and Northern trial roses with Vance’s races to have that data to begin to compare with field trials. We have that race data and I presented on it at the American Society for Hort. Sci. meetings this past summer. When I have more time I’m looking forward to writing that article up to get that data out there.



race specific resistance (typically a single gene governing it

David, do you know if ‘race resistance’ is associated with particular membrane receptors in the rose that exhibits it? In more general terms, is it known whether or not Diplocarpon gains access to the plant cells through a receptor mediated mechanism?

We have that race data and I presented on it at the American Society for Hort. Sci. meetings this past summer. When I have more time I’m looking forward to writing that article up to get that data out there.

Any idea when we might be seeing this data :slight_smile:


Am I right thinking I have this race C as for me after initial year Love and Peace defoliates just as the average HT.

And is horizontal resistance comparable to foliage durability.

Title: Partial resistance to black spot disease in diploid and tetraploid roses: general combining ability and implications for breeding and selection.

Author: Whitaker, Vance; M.Hokanson, Stan C.

Published in: Citation: Euphytica Oct2009, Vol. 169 Issue 3, pages 421-429, (2009)

Abstract: “Black spot disease, incited by the fungus Diplocarpon rosae Wolf, is the most important disease of roses ( Rosa hybrida L.) in the outdoor landscape. Though partial resistance exists in cultivated germplasm, the genetic basis of this trait has not yet been elucidated. Six diploid and six tetraploid rose cultivars were crossed in two factorial combining ability arrays. Whole plant and detached leaf inoculation methods were used to assess partial resistance under two different disease pressures using a characterized single-spore isolate. Parents from both arrays had significant general combining ability effects across multiple inoculation methods and environments. Specific combining ability was not significant for either array. Parent per se performance was highly correlated with progeny performance on a family mean basis. High positive correlations among whole plant and detached leaf inoculation methods indicate that detached leaf assays can substitute for whole plant assays. Based on these results, a breeding strategy including parental selection and early, among-family selection is proposed. To our knowledge, this is the first investigation of combining ability for disease resistance in rose.”


If you even look at Love and Peace (HT) here, it will blackspot. It has from the very first day it was introduced here. here are better yellow/red blend HT’s to be had, in my opinion. For example, Funkuhr is 20some years older and is very clean here. I think cuttings can be had via request from Washington Park.

Playgold is one of the cleanest minis I have ever seen to exist. Usually minis look sad with blackspot and mildew by the time July rolls around, but Playgold always looks happy.

My garden(NRW,Germany) seems to be an excellent breeding ground for blackspot (no fungicide use, sometimes a bit of picking infected leaves).

New Dawn is here blackspot infected, as well as all Austin roses. My old roses are also not better (Louise Odier, Honorine de Brabant, Madame Alfred Carriere). The difference seems to be whether a cultivar is vigorous enough to get going again, when the fungal pressure decreases.

Some of my seedlings are doing better then anything I bought, but they still lack other qualities.

The only plant that never had a single spot of whatsoever is a species hybrid (2007) with some rugosa in it, but I am still waiting for flowers of this plant.

Of particular interest (to me) in the Whitaker and Hokanson blackspot paper is their finding that, of the 12 commercial roses tested, the diploid shrub rose Pink Gnome (BAIpome) was the only one completely resistant to the strain of blackspot used. Also, 6 of the 30 seedlings raised from Pink Gnome were also completely resistant. Pink Gnome parentage is NOAtraum

Pink Gnome parentage is NOAtraum

I might try Baby Blanket next year:

Flower carpet is Immensee x Amanda (Authur Bell and Zambra) whereas Baby Blanket is White Immensee x Goldmarie, which seems like a better choice to me. I have tried the similar Electric Blanket this year, but could not get it to set seed =( I should probably go back to using Carefree Marvel, though, as it seemed to produce good results. I think it helped to have been line bred; it has multiple (at least 5) instances of Rosa wichurana in it.

Regarding flower carpet in any of the colours (except the deep single red one so far) all spot badly here early in the season but then recover and show no sign for the rest of the season. Also prone to what looks like cercospora. I also suspect they are all triploids and so far I have had trouble getting the flower carpet seeds to germinate. The most successful one, so far, has been the scarlet flower carpet (the semi double red one) though the seedlings don’t seem overly thrifty. The original pink one set loads of OP hips but so far none have germinated. The flower carpet pollen seems to work on a few things (I tried them on tetraploids mostly) but again, so far none of their seeds have germinated (though it is early days).

Red blackspots bad here. At the wholesale nursery I work for, Flower carpet Scarlet seems to be the best in health.

A couple more findings that I forgot to add:

Home Run does appear to suffer from some sort of leaf spot. Last year around this time it was perfectly clean at Longwood Gardens. This year, all of the Home Run bushes seemed to have lost the bottom half of their leaves to some sort of leaf spot. Granted, most roses are nude by this time of year, but I was surprised to see any defoliation.

David is correct with New Dawn, Carefree Beauty and The Fairy. They are all grown at Longwood Gardens and while not disease free, they hold on much longer than most. New Dawn in particular is such an amazing rose combining outstanding disease resistance, hardiness, flower form, repeat and decent fragrance.

Here’s my list.

KO of course (& 2 or 3 or so KO seedlings)


Carefree Delight x R. multiflora seedling (once blooming)… rock solid in the disease department.

‘Niota Pink’…once blooming found rose.

Konigen von Danemark …once blooming.

For repeat ‘exotics’ the best would be Golden Showers, Arthur Bell, & Rosette Delizy so far for me.

I own The Fairy & Carefree Beauty and the three above have similar disease performance.


You reminded me about Carefree Delight. It is another that holds up very well to disease, similar to The Fairy. Not disease free like Knockout, but very resistant.

I experimented with Rosa Rugosa Rubra a few years ago crossing it with modern roses. I was not very successful. None of the hybrids are as disease resistant as the parent.