Home Run Bug?

I have been out looking at the roses to see what diseases are active, and on which roses. Winter is our best chance to get black spot here. I noticed that my ‘Home Run’ had small black spots (way smaller than the usual black spot disease that we sometimes see here), along with purple splotches on the canes (looks like the badly affected canes might die back). Some of the spots on the leaves are irregular in shape.

This same disease is present on a few of my other roses, but not many. The lesions on the canes look like downy mildew, but the spots on the leaves are different from anything that I have seen. Also downy mildew usually only hits in March. I have noticed that both ‘Baby Love’ and ‘Home Run’ get downy mildew better than most.

Any ideas???

Jim Sproul

Cercospora perhaps?

Link: www.ars.org/About_Roses/disease_cercospora.html

I have found that a lot of my most disease resistant roses develop cercospara. I have one Darlow’s Enigma seedling that is more disease resistant than Darlow and it gets a little cercospara every Summer. Belinda’s Dream gets it also.

Patrick

That’s really interesting Jim,

A local nursery had problems with some purple stem lesions on their ‘Home Run’ and to a lesser extent ‘Knock Out’ bareroot roses. They tried to send them in for diagnosis, but they weren’t able to give a definative answer. New growth above the stem lesions would wilt and die and/or be stunted. The bareroot plants came from the West Coast.

There was a good case of blackspot on ‘Home Run’ in the center of the plant at the MN Landscape Arboretum in 2007, but not 2008. The lesions were smaller and much less severe than on most of the other roses.

David

Curious. I haven’t seen this happen to my ‘Home Run’ (yet?), but mine is kept in the greenhouse in a container, for breeding. I might get a second and plant it outside where it gets plenty of exposure to Cercospora and see what happens.

It would be interesting to find out if there is a connection between Blackspot resistance and Cercospora susceptibility!

Paul

Both my Baby Love and Home Run are clean of everything-- BL for about 8 years and HR since it was introduced. The only difference between the two in my garden is that Baby Love is easy on the eyes and Home Run looks like the most boring floribunda ever :stuck_out_tongue: It doesnt even look like a shrub here… Then again, Baby Love just looks like a super fat miniature. There is nothing “shrub” about these two roses imo.

Jim,

I have seen tiny black spots on Home Run leaves as well, but it is never widespread and I have never seen any leaf loss from it here in PA where blackspot and cercospora defoliate everything. Assuming it is the same thing, I would not be too worried about it.

Shane

We all garden in different conditions. Here Home Run gets fair share of BS, but still keeps more then 50% leaves. It also gets Cercospora in the fall and defoliates from it, but somehow, because it happens when it is almost time to shut down anyway, I take it easy. BS bothers me much more. I actually love the look of HR blooms.

Baby Love is much less resistant here, basically naked from BS from mid June. Don’t grow it anymore.

Olga

Each fall I strip leaves from my greenhouse mother plants in preparation for storing them (in a root cellar) for the winter. One side of the greenhouse walls is raised for most of the season for better air circulation. Each autumn I look at Home Run and the foliage is immaculate. Then I start stripping leaves and the canes are a mess. By the time I finish pruning what I thought was a healthy rose it has been reduced to a few canes. One year I cut the entire plant back to the crown. I have also experienced this with Knock Out–much like David said. Many of us spend a great deal of effort trying to breed out foliar diseases but to me the diseases of the canes are actually much more devastating and I find it awfully perplexing. The lesions do resemble Downey mildew but I have always had major defoliation as part of the symptoms. Paul’s thought about a connection between black spot resistance and possible Cercospora (if that is what it is) susceptibility makes me shutter.

Julie

Thanks to all for the thoughtful insights.

I am nearly certain that this is not Blackspot, but I know nothing of Cercospora. Reading a bit about it though, makes me wonder if what I am seeing is something different. From what I’ve read, it sounds like Cercospora is a warmer weather fungal disease. This started during a colder part of our season.

I wish that I had taken photos when the leaves were green, but I will try to take some of the brown leaves and canes. To me the cane lesions look just like downy mildew, but the leaf spots are different.

What bothers me most about all of this, is I think that we are going to have a rough time breeding really clean roses. I think that we may just end up producing plants that will attract less prevalent diseases that will ultimately become new main players in rose diseases…

Jim Sproul

What about canker? Or is that just here in the cold north?

Well there is Anthracnose which is usually in rainy season and late Spring but you never know.

Patrick

Years ago I had the opportunity to have my local Ag Agent test the foliage of ‘Basye’s Purple’ to see what the ugly purplish spots that always developed on it in the early Spring were. Tests confirmed that it was Anthracnose, which normally has a rather different appearance on other roses. The point being: fungal diseases take on different physical appearances on plants of widely different classes. I suspect the spots that commonly appear on ‘Stanwell Perpetual’ are also Anthracnose or perhaps Cercospora, but these are disregarded as “just something it does”, since it has no apparent impact on the plant’s health.

Paul

Well I took some photos of what I am seeing. Though the leaf photos are not “fresh”, I think that they show enough to suggest that it is not Blackspot, and not typical of Downy Mildew.

The first photo is of a ‘Home Run’ leaf upper surface:



Next are photos of the upper and lower surface of another ‘Home Run’ leaf. You can see that the spots do not go through the leaf as is seen in Blackspot.





Then, below is a ‘Home Run’ cane showing the lesions on the cane.



Finally, the last photo is of a new 2008 seedling showing the same sort of cane lesions. It’s parentage figures heavily with ‘Baby Love’.



Very few other roses are affected. Perhaps this infection is a good sign???

I will watch for whether or not the cane lesions result in cane death or die back.

Jim Sproul

Is it canker (in the stems)? Sometimes I get this patterning in winter too with varieties that seem less cold hardy (like the miniature ‘Suntan’). It shows after freezes and develops into a canker like die-back. I dug all the ‘Suntan’ up last winter and replanted them below the graft to encourage rooting above the graft because they were badly affected like this and died back so far. This purpley blotches joined up evenuatlly turning the whole stem purple (before it died). Others had it and recovered.

My opinion:

-The first picture doesn’t look like blackspot to me. It could be cercespora, because of the lighter, grey, centres in some of the spots.

-The second leaf does look like blackspot. Especially at the top of the leaf in the picture you can see the typical serrated edges.

-Home Run might show spots with a different characteristic because of it’s partial resistance to blackspot (speculating here).

Rob