In the late 1980s, Cornell University developed and tested a spray for black spot and powdery mildew on roses that is now known as the Cornell formula. It consists of, mixed into one U.S. gallon of water, two Tbsp of ultralight horticultural oil and one heaping Tbsp (four Tsp) of baking soda. If the oil doesn't contain an emulsifier, then a Tsp to a Tbsp of a mild liquid dishwashing soap can also be added.

Many of us who have used this spray for years have found it to be very effective, so Jan is on the right track.

here is a spray to both feed and protect roses, 2 tablespoons of hort. oil, to 4 litres of water. 1 tablespoon if liquid soap, 1 tablespoon of fish emulsion, 1 tablespoon of baking powder, and liquid fertiliser of choice.Spray on dry leaves.

suziebee, that is essentially what is known here as the Modified Cornell Formula. I'm happy to see it's made it down your way. Here's a link -- scroll down to Organic Spray Formula.

Here is a link that might be useful: Rose Care

Field, thank you for the link, very informative. What are your thoughts on copper sprays? I seldom use sprays on my own roses, only at work unfortunatly.

I used copper and sulfur sprays back in the 60s and 70s and never found them to be as effective as I have found the Cornell formula to be.

Copper, although considered "organic," calls for more caution than the alternatives. If used continually for a long time, it might build up to harmful levels in the soil (or possibly in your liver). Occasional use with due care is safe. It is a broad spectrum fungicide/bactericide and useful for special problems like canker, gall, anthracnose, or downy mildew.

At the moment I spray; Winter oil, Spring copper, then if necessary a garlic and pyrethrum spray over Summer. This is only in the gardens I have control over. I have found the more money people have, the more they expect perfection in their gardens at any cost, including my liver.

Suziebee, in your Oct. 9 post your formula called for
baking Powder, where the others mentioned Soda.
Is this correct?? Does anyone use powdered or liquid
molasses??

Cornell Formula works for me and my 100 plus roses

Here is one I got from a book:

- 1 teaspoon baking soda
- 1 teaspoon oil (any oil will do, like cooking oil)
- a few drops of liquid soap (I use natural dishwashing soap)
- 1 litre of water

This is much like what Elks proposes above, with the added benefit of oil, which makes sense as it helps to make the mix stickier so it stays on longer.

A word of advice, though. I find that if I start with the water and add the other ingredients to that, this will hardly ever become a homogenous mixture. Therefore, I would try mixing the baking soda, the oil and the soap really well first and only then diluting this slowly with the water.

I just sprayed two pumpkins with this (they caught it from a pair of garden center bought zucchini - so much for buying started plants!).

I used a brass plant mister for this (see link below). While this may be far from being a standard garden tool, I find this works better than other implements as it really creates a fine cloud of mist that can reach where other tools can't (we all know how tough it can be to get the stuff UNDER the leaves, where it really matters). When almost full, you can even turn it up to target leaves from below and still works great. Also, because the mist is so fine, there is less waste and also less of a chance of overdoing it and burning the plant. Just saying, because I have been wondering if it just might be that those who complain that baking soda doesn't work for them are simply not applying the stuff right.

I'll let you know what gives.

Here is a link that might be useful: Brass plant mister

I used the recipe I posted above and it looks like it is working. A zucchini got some very superficial and small scars on one leaf, but other than that, no burning. The existing fungus is still there, but it has stopped progressing.

There are even affected and unaffected leaves rubbing each other, but the unaffected leaf stays unaffected. I hope it's not my mind playing tricks on me, but it looks like the leaf that got a bit of scarring also has less fungus now. Instead of the entire leaf being covered with it, now, only the lower edge of the leaf shows white stuff (looks like I washed the fungus off with the solution, and some of it got stuck at the edge of the leaf). Maybe this one leaf got a higher dose of solution, which would explain why the fungus seems to regress on it and at the same time why there is a bit of scarring there.

We have been having some bad storms for the past two days, so it is time to apply again. I think I will add a bit more baking soda this time, just to see if there is actually a way to dissolve and wash off dead fungus. I don't mind losing the zucchinis to baking soda burn--they have not produced so far at all and are so small that I don't think they will ever fruit either way. So, the zucchinis are one of my little garden experiments this year.

I will post again to let you know how it turns out.

The link below is a very good summary of using baking soda as a fungicide.

Here is a link that might be useful: Baking Soda as a fungicide

Kimmsr, that's a pretty good link. I am bookmarking it.

So, it would seem that it is possible after all to actually eliminate PM instead of just keeping it from spreading. This has also been my observation. It is also interesting to read about the addition of surfactants. It seems to me that many gardeners simply mix baking soda with water without adding much else. This may explain why many gardeners report that baking soda doesn't work.

Baking soda has worked well for me, even to the point of washing the fungus off, and I think it has to do with the addition of cooking oil.

Even if you make your soil into a good, healthy soil that can be an aid in keeping your plants disease free that still will not, necessarily, protect the plants from Powdery Mildew or Black Spot. Growing plants in a good, healthy soil so they are strong and healthy will help protect those plants from disease pathogens and if the plants do get infected can help those plants fight off that infection, but good, healthy soil is not a guarantee that your plants will never get a plant disease, so we need some things that can help.
Simply washing your plants leaves can be an aid to preventing disease because the pathogens that cause those diseases get washed off, although allowing a plants leaves to stay wet too long can encourage some disease pathogens to grow and infect that plant.