Mix 1 Tblsp baking soda in 1 gallon of water and add a tiny drop of liquid dish detergent or 1 Tblsp of Murphy's Oil soap. Spray once a week preferably early in the morning. The baking soda changes the pH and the soap releases the surface tension of the water on the leaves.

Nancy the nancedar

thanks Nancy. I knew there was something like that.

I think i need to use some of that on our hydrangeas as well.

If that actually works on your roses, let us know. I have to use much more aggressive sprays to keep BS barely under control on my HT roses. Emphasis on the barely. Very hard to keep in check.

I used the corn meal the first time this year and so far have not had black spot show up, even on my HT's. I'm impressed so far.

Here goes a dumb question hb: you sprinkled the corn meal around the rose bushes, right? And where did you find the corn meal? It seems that Lee Reich (who wrote Weedless Gardening) uses corn meal as a fertilizer, but I may not be remembering accurately.

The leaves on my Hydrangea (which all came from cutting) are fine but the stems have dark spots on them. Mostly dark brown maybe leaning towards black. Is this what you are referring to or is this something different? Or, is this normal?

Scott

Scott, no my hydrangeas have spots on the leaves, just like my roses. I'm not sure if that would be the same thing on the stems or not.
dirty sc you can find the cornmeal in the grocery store right next to the flour.
Thanks for everyone's help!

Black spot on rose is caused by fungus Diplocarpon rosae. It is not same fungus that causes fungal spot on hydrangea or other plants, although warm moist conditions and lack of air circulation can promote fungal infections by different fungi on different plants in a garden. So is pH the mechanism that makes baking soda/soap and corn meal work to prevent fungal infection? I'll have to try that. I hesitate with "natural" remedies sometimes becasue they can be worse than the synthetic solution. Recently I read that 1ppm (part per million) detergent run-off into ponds is enough to kill tadpoles. It has made me think twice when I think of soap as innocuous.

Sorry about the late reply about the cornmeal. I get the small bags at the grocery store because I only have 10 roses around the yard and it treats the whole lot of them. I just sprinkle around the base through the dripline of the rose and cover the unsightlyness with mulch. My neighbor uses some kind of fungicide and says he's having problems with BS so I'm glad this seems to be working. I just got another bag last week but haven't spread it yet but think it will get me through the end of the summer.

Brenda_near_Eno and all - Isn't detergent a lot different than soap? I thought that detergents were petroleum-based and that soaps were either vegetable- (castile) or animal-fat based. I know that detergents can kill tadpoles (that stuff is highly toxic to fish too) but isn't soap supposed to be be non-toxic to them and that it also biodegrades??? I would also think that the tiny amount used for BS is a whole lot less a major run-off problem than the huge amounts of detergents we use for bathing, washing clothes and dishes, cars, decks, etc., let alone hair, pets, and carpet if we live on a hill or have streams, ponds, or leach-lines (as part of septic systems) on our property? I've used the baking soda and soap solution for 20 years - Ivory Soap, Murphy's Oil Soap, and dissolved Castile Soap mostly. Sometimes Dawn Detergent because of its grease disolving properties (against the naturally occuring waxy coatings) on thick leaves like Canna and Cabbage against a host of sucking and chewing insects - and quite effectively too. Bottom line is that I would rather have a little bit of soap than the residuals from Sevin on my food or flowers.

Nancy the nancedar

So, Dawn works for JB's?

Well, Nance, you should know me long enough not to awaken my geekiness! Soaps can be natural or synthetic, so there's no "natural" component to either of them, to my understanding, other than soap can be found in nature (yucca plant contains some I think?) or chemically synthesized. (Homemade soap is typically just a chemical synthesis that we all feel comfortable with, because it can be done easily in a big iron pot - saponification of fatty acids in animal or plant fats- still synthetic as any chemical factory.)

Soap and detergent are different molecular types, but they have the common property of hydrophobic end (oil-loving) and hydrophilic end (water-loving or ionic). Thus they dissolve grease by surrounding the grease molecules with their oil-loving ends - then the water-loving ends of the molecules interact with water molecules to float happily away, carrying the surrounded "grease" molecule along. Surfactants basically do the same thing, and soaps and detergents are surfactants. These molecules will interact this same way with grease on a dish, natural oil on your skin, and waxy components of amphibians and insects. CONCENTRATION and exact chemical structure are important in how strong ("strong" meaning "effective" or "harmful", depending on whether you are washing clothes or spraying a frog) the properties will be. In general, detergents are stronger than soaps at equal concentration, I believe.

Ivory bar soap is soap, with some salts and fragrance added.

My understanding, and I can't find definitive answer, is that Murphy's Oil Soap is not soap and not oil? The ingredients are not published or divulged(?). The MSDS (Material Safety Data Sheet) lists ecological effects as unknown.

There are lots of versions of Dawn, but original Dawn ingredients are : "water, sodium lauryl sulfate, sodium pareth-23, sulfate C-12-14-16,dimethyl amine oxide, SD alcohol, undeceth-9, propylene glycol,cyclohexandiamine, polyacetate, protease, fragrance, FD&C blue, no
phosphate." Sodium lauryl sulfate and sulfate C-12-14-16 are detergents. Sodium lauryl sulfate is in lots of things, like dish soap and toothpaste. There is differing research concerning possible harmful affects. And don't even get me started on "protease" - I would not wash my hair with Dawn, though some people swear by it.

In my own opinion, I would use soap on my person and sparingly maybe on my plants. I use detergent when it is needed, not on me or my plants, and I like that my dishwasher spares my hands from exposure. I do not think of either soaps or detergents as harmless. It's all just a matter of concentration. Environmental chemists have a saying - Dilution is the Solution - but in our fast-developing world, we're just running out of the possibility for dilution.

Here is a link that might be useful: Scary opinions? of sodium lauryl sulfate

Here in the sandhills of NC I use a mixture of skim milk and water (1:1) to stop and/or prevent black spot on my roses. I've only had to use it once so far this year. I think I heard about it on one of those gardening shows.

So Brenda- what I need to know now is what kind of shampoo do YOU use? LOL :) That's scary stuff in that link!