The state-of-the-art rose fungicide is Bayer Rose and Flower Disease Control containing only tebuconazole (not the combo products), available at most Lowe's. It will stop the disease. Spray once a week for 2 weeks and then every other week until the dry season arrives.

In zone 6 you should slightly bury the graft swelling (where the canes diverge) to keep it from freezing.

If drainage is poor, raising the grade even 4" can help.

You definitely need to spray fungicide. I have for many years successfully used BannerMaxx which like the Bayer product is a conazole systemic fungicide. These do not kill fungus but rather are fungus growth inhibitors. They are widely use in agriculture and even medically for fungus afflictions like athletes foot. You have to buy BannerMaxx on line but it is much cheaper and less bothersome to use than any off the shelf fungicide I ever used. The mix rate for Banner is 2/3 tsp. per gal. and the recommended application rate for roses is every two weeks and it absolutely works.

Henry, tebuconazole (Bayer) has been proven in a thorough scientific study to kill blackspot within the leaf even after spots have been expressed, a week or two after germination. If the local infection is not too far advanced, the leaf will live for the season. Propiconazole (Banner) almost certainly does the same thing, but I haven't seen a study. It is known to be curative of some other fungal diseases. What Rosemania says about the action of surface and systemic fungicides is backwards wrong.

Michael, tebuconazole and propiconazole are members of a class of fungicides that act as ergosterol biosynthesis inhibitors (epi). Ergo means having to do with fungus (ergot), a sterol is an essential constituent of cell membranes and biosynthesis is the synthesis of more complex molecules from simpler ones. Epi fungicides work by inhibiting (preventing) the synthesis of an essential element of the fungoid cell membrane. Therefore epi fungicides like tebuconazole are only preventative and nowhere have I ever seen them indicated otherwise. Henry

All very confusal, as Winnie the Pooh would say.

I have always "been told" (I think this is coming from the Houston Rose Society) to use something like mancozeb or the Bayer product to cure blackspot which is already in existence on the plant but once cured, to then use, alternatively Compass and/or Honor Guard. Compass and HG will then PREVENT new blackspot from emerging.

Thoughts?

Lynn

oh..I love it when people talk biochemistry to me. Wonder if mother nature can read.

Linked is a massive blackspot study done by a Kenyan woman at a German university that has a lot of new information.

Henry-- go to pdf p. 85 for a picture showing the curative power of tebuconazole (Bayer). These leaves were treated with various fungicides 3, 7, and 10 days after inoculation and infection with blackspot. Then the photos were taken 20 days after infection.

Lynn-- in the same study, strobilurin fungicides (for ex. Compass) were found very effective as preventatives. As the picture on p. 85 shows, they are, as you say, not curative. However, Compass should not be used by itself much because of the danger of resistance developing. Honor Guard is propiconazole, the same as Banner, and similar to tebuconazole (Bayer). So you should have Honor Guard and Bayer in the same category. They are both preventative and curative.

As far as I can tell, the claim that mancozeb is curative is a gardener's old wives' tale disseminated by Rosemania. It is a very effective preventative if it coats the leaf surface completely. The mfr. doesn't claim curative ability, nor is this mentioned in scientific literature. Mancozeb is not systemic, so how could it kill the fungus within the leaf?

Here is a link that might be useful: blackspot dissertation (pdf)

Michael, I don't believe that this study shows curative power nor does the author make any such claims that I can see. The effects of the fungicide application are shown in various ways for immediate, 3 days post infection, 7 dpi and 10 dpi. What about 20 dpi or more? The point of the study is to explain how the fungus works to infect the rose and compares the effectiveness of four fungicide types. My conclusion would be that each one stopped further development to various degrees but that all were essentially preventatives. The paper did not really discuss the different products in a scientific way but rather used analysis of controlled experiments. You draw some conclusions based on what seemed to have happened but you can't say something is so unless you know why it happened. I believe there is ample proof that tebuconazole is a preventative based on how it works and nothing in this study indicates otherwise. Henry

got that Enita? Me neither

I am defecting to the Snapdragon forum

There is a 2009 published paper with the thesis writer as one of the 3 authors. See:

http://www3.interscience.wiley.com/journal/121516243/abstract

henryinct, I do not have your e-mail address. I can send you further information about this paper.

kuska@neo.rr.com

Here is a link that might be useful: link for above

Before y'all get any more convoluted, Might we back up, ask what the rose in question is, where it was purchased, and whether it was bare-root or containerized?

'Cause, at this point, the poor OP is going to spend more $$$ on chemicals than he/she did to begin with on the rose.

If you DO decide to use a chemical fungicide, PLEASE do your homework, first.
Read the on-line literature about the chemical in question.
And, please, please wear protective gear, including a respirator and chemical gloves, if you are going to spray.

Jeri

Henry, Thanks, I would like the paper. My email address is below. The abstract indicates that the paper is about controlling BS and probably makes most of the points of the dissertation. The point of contention is whether tebuconazole is a curative as well as a preventative and I think it is not. In the study the fungicides were applied before infection, at time of infection, and 3,7 and 10 days post infection and pictures were taken 20 days post infection. The infected leaves treated with tebuconazole looked the best after 20 days but there is a period of at least 7 days and possibly much longer (the latent period) that it takes for the spores to germinate into fungal cells In other words, a preventative could still work 10 days after infection. If it was applied 20 days post infection that would be another matter but this was not done possibly because the fungicides used are known to be preventatives. In the case of tebuconazole, the action is to inhibit the development of a factor necessary for fungal cell membrane formation.

Forgive me but I actually find this stuff interesting. My e-mail is henrylbs@hotmail.com Henry

(continuing hijack :)

henryinct-- Tebuconazole (Bayer) kills the developing fungus inside the leaf.

Elsewhere in the study, she describes how, inside leaves treated with DMI fungicides such as Bayer, the chemical destroys existing fungal structures. She includes microscopic photographs showing this destruction. There is no need to theorize, you can see it happening.

Respectfully, it is incorrect to say it takes 7 or more days for "the spores to germinate into fungal cells." She observed spores germinating in 7-8 hours when wet at the appropriate temperature. Within 7-10 days at favorable temperature, there are externally visible symptoms.

If you look at the tebuconazole column on the right (leaf pictures, pdf p.85), the middle leaf has tiny spots which probably had formed 7 days after infection and were arrested by the tebuconazole treatment at that time. (A poster here, Pete in Daytona, observed this happening a few years ago when the product first came out.)

In the lower right-hand corner, the obvious spots that had formed 10 days after infection were arrested at that stage by the tebuconazole treatment at that time. Elsewhere in the study, she says that such leaves do not finally succumb to blackspot but continue to function. However, if the infection was more advanced at the time of treatment, the leaf has already been damaged too much and will die, even though the chemical kills the fungal body.

Michael, the paper that Henry Kuska emailed me contains everything of importance in the dissertation but it is much better written and it is easier to understand. Perhaps he could email it to you. Read it and you will see that tebuconazole does not kill (or arrest) fungal cells but it is able to prevent their formation even 10 days after infection. The authors suggest that the reason for this result may simply be that tebuconazole is "more systemic" than the other three fungicides tested in the study.

I find some yellow leaves in the lower part. too later to cure the fungus?

Henryinct,

I have read the paper by the same author that HK found and kindly sent to us.

This paper also refers to the "destruction" of fungal structures established with the leaf when tebuconazole (Bayer) is applied "curatively" after infection (p. 4) and says "the fungus is killed" (p. 7).

Bayer is both protective (preventing the disease from establishing within the leaf beyond a minimal temporary invasion) and curative (capable of disabling a fungal body established for 10 days and starting to sporulate). If you want to call this latter effect "prevention," OK, but that is not the common usage.

Enita, sorry about all the babble.

Blackspot does not make the whole plant sick. It attacks each leaf separately from outside. Leaves that are already yellowing around black spots will die. Leaves with only small black spots will probably be cured if you apply Bayer immediately. It will also prevent any further infection. See my first answer to your original post. If you want to make sure, spray every week as long as rain is expected.