ADR rating may not be enough....

7 years ago

I finally was able to read the 29 page ebook from the ARS on rose diseases that Henry_Kuska kindly provided the link to. The statement that really got me was:

"Cercospora leaf spot may be a problem if BS resistant cultivars are being used and fungicide sprays have been eliminated."

Breeders are now directing their attention to this disease as it is becoming more prevalent."

The writing also clearly describes the difference between a 'resistant' rose and a 'tolerant' rose. It would appear a tolerant rose is preferred because it will continue to grow and bloom despite some disease. Whereas a resistant rose is only as resistant as the trial indicates - most set at less than 50% indication of disease and defoliation.

It has long been clear that there is more than one disease going on in my gardens. Especially when my ADR roses are showing the same leaf spotting and defoliation as the other roses.

Cercospora responds to the same fungicides and spraying routine as BS but it would appear that the ADR rating is overrated if it only pretains to BS and maybe powdery mildew or rust.

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FrozeBudd_z3/4

7 years ago

"Cercospora rosicola is perhaps less common in Germany where the ADR trials are?" ...

To that I am uncertain, though I take my chances on varieties that have a displayed a proven health record above others. Yes, occasionally they haven't held up so well, though for the most part others have been very clean, many of which are Kordes roses.

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Comments (7)

rifis (zone 6b-7a NJ)
7 years ago
Is cercospora causing defoliation of your ADR roses?

If so: which roses, and when did you first realize it was the responsible agent?
rifis (zone 6b-7a NJ)
7 years ago
According to U of Florida IFAS Extension, Cercospora rosicola is distributed worldwide. And the format for ADR scoring is well described; Google Translate is not even needed for English-only speakers.

Of course C. rosicola may behave differently over there.
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FrozeBudd_z3/4
7 years ago
last modified: 7 years ago
I don't spray my roses and they had been handling black spot decently well, though then along comes cercospora that at times has completely (and repeatedly) defoliated bushes from top to bottom in particularly bad years. I've now mostly switched to varieties that have shown strong disease resistance over a large continental range.

With roses ... it's always something !!
mariannese
7 years ago
Cercospora rosicola is perhaps less common in Germany where the ADR trials are? I've searched for it on Swedish rose sites and haven't found any sources describing this disease.
jim1961 Central Pennsylvania Zone 6a
7 years ago
I have also seen roses here highly resistant to blackspot lose all there leaves to Anthracnose disease....
diane_nj 6b/7a
7 years ago
Also remember that there are 13+ strains of blackspot.