A worthwhile experiment requires replications.

So, to run a meaningful test, you need more treatments:
1. A control -- that is, no treatment.
2. The dissolved aspirin without the non ionic surfactant
3. The diluted non ionic surfactant without the aspirin.

Then, too, these additional guidelines define true experiments:
1. All plants (here, roses) are the same kind and age.
2. And all the plants (here, roses) are growing under the same environmental conditions.
3. And all the plants (here, roses) receive the same day-to-day care.

Without all the above in place, you are dealing with chance and/or coincidence.

I may have part of the answer regarding why aspirin may be of some use. A few years ago, I had a class in plant pathology during my university years during which we had discussed methyl salicylate's role in plant disease. We had come across a paper in a scientific journal relating an experiment on tobacco plants (frequently used in research because they'll catch almost any disease imaginable and they're cheap and easy to grow) following the discovery that some plants, when infected by some disease, gave off some of it in the form of vapor. What was observed was that the neighboring plants, although eventually attacked as well by the same disease, showed less severe symptoms. An experiment was then conducted under controlled conditions during which tobacco plants were exposed to the compound. What was found was that methyl salicylate did in fact improve the plants' ability to withstand disease.

So what happenned ? I can't remember what was said in the paper following the results, but the answer undoubtedly lies in what are called elicitors and messengers. I'll spare you the details (and for myself, the task of digging through my old school notes in some forgotten corner of the basement) but the big idea of it is that some plants produce certain chemical compounds under certain stresses (such as disease) which may evaporate out of the plant and be dispersed in the surrounding air. Neighboring plants of the same species would then, upon contact with trace amount of the messenger chemical, react by producing increased quantities of some compounds which increase their ability to withstand stress (such as additional cell wall material, certain plant hormones, increased quantities of wax on the leaves which would slow fungal attack).

This may sound far-fetched, but keep in mind that plants are highly complex organisms and that most of them do have some biological or chemical way of reducing their susceptibility to disease. Of course, not all plants may produce methyl salicylate, not all plants may react to it, and not all plants may produce volatile compounds. But within the same plant, there are often distinctly observable reactions in healthy plant parts when one of them is under attack by a pathogen. As I said, there may be more wax production, there may be a change in leaf orientation on new growth (in order to reduce moisture retention on the leaf surface, thus reducing the ability of some pathogens to survive before penetrating the leaf surface), there may be changes in the chemical make-up of sap and so on. Reactions such as this have repeatedly been observed in many plants under stress. While it may not always allow a plant to ultimately survive the disease, it may allow it some extra time to flower and set seed, thus allowing it to reproduce. Imagine the population-wide advantage of having stumbled upon the ability to communicate such information as the presence of disease !

Anyhoo, back to your roses and black spot. Perhaps roses would react to aspirin, perhaps not. It's certainly worth a try in my opinion and I dout it would harm the plants. One thing it will certainly not do, however, is act as a fungicide; at best, expect a reduced incidence and/or severity of black spot on the plants you'd have sprayed with aspirin.

Some people might object to spraying man-made compounds such as aspirin in their yard even though it does occur naturally in some plants (like many other synthetics, which naturally occur in several life forms), but that's a matter of personal opinion. If you're one of those people, but you're intrigued by this whole aspirin idea, you might want to try researching willows or wintergreen. Aspirin was first developed from willow leaves (indians used to chew them as a cure for headaches) and wintergreen contains methyl salicylate, so there may be some way to use them as a natural plant spray. I have no idea if it would work, this is purely hypothetic, but who knows....

I hope this has been informative....good luck !

But does any of this qualify as an organic method?

It might if you got the salicylate from the original source, willows.

First, thanks to Iwoqax for posting some of the science behind this experiment. It is a complicated subject with ongoing research taking place.

To Jean - You have, of course, stated the correct method of performing an experiment. However, in this case I know that there are many out there growing one or two roses they love which develop severe blackspot every year. All of us keep trying organic methods as we hear of them in hopes that one will work. I just thought that there might be a few interested parties out there who would want to trial this idea. When I first posted and began promoting the idea of cornmeal as a plant fungicide on GW I had no idea where testing would lead us. Although cornmeal has proved to be a very successful fungicide (and fertilizer) for many situations I have not found it helpful for blackspot or tomato problems. However, some gardeners have, judging from the emails I have received. Ditto my asking people to use granulated sugar as a method to control root knot and ring nematodes. I have received emails from people very pleased with this method and also including before and after soil sample tests done by their local extention offices which prove that sugar controls nematodes. So, here I am again, suggesting that the experiment for black spot I detailed above may or may not have some merit. We won't know unless we give it a try.

To Field - I was waiting for you to post your thought...is this an organic experiment? The surfactant I suggested is organic. It is up to each person to decide if aspirin is organic. It is the only salicylate I can think of using that would give us a measured dose for each treatment. There are a number of plants high is salicylates, but extracting the same amount each time from these plants without lab facilities would be difficult for the average gardener. This is why I suggest using aspirin for this test.

It is up to each person to decide if aspirin is organic.

Aspirin is a man-made chemical. It is a derivative of Salicylic acid.

Was said:
"there are many out there growing one or two roses they love which develop severe blackspot every year."

Another option worth considering is to replace it/them with less susceptible kinds.

Is aspirin organic? Technically no, but let's look at the reason WHY we go organic. A good part of the reason why folks go the "organic" route in the first place is that it is not harmful or as harmful to humans as going the BannerMax route. So if humans can orally ingest aspirin, I think it would be safe to inhale it some of it when spraying in the garden.

If I have extra time, I just may try this aspirin recipe.

Angie