After publishing my last post on spraying non-toxic stuff, instead of the usual fungicides and pesticides, I was reminded by my good friends, Diane and Dick Lawson that they are spraying almost exclusively Castile soap on their garden (which is one of the nicest in the Twin Cities).
Here's the address of my last post: http://theminnesotarosegardener.blogspot.com/2013/02/hazardous-roses-3-spray-nothing-toxic.html
I asked Diane, a recently retired high school physics teacher, to explain exactly what Castile soap is vs. the liquid dishwashing soap I've been using and was recommending in my article. I was surprised when Diane told me that Castile soap is made primarily from olive and other vegetable oils, which presumably leave a beneficial coating on the plants, vs. detergent soap. In other words, Castile soap is a natural surfactant that remains on the surface of the leaves, much as a surfactant fungicide might, as well as acting as a deterrent to insects.
I remember using Diane and Dick's Castile formula on my garden a few years ago and that was the summer I saw virtually no thrips or aphids. Diane would contend that's the case in her garden every year.
Until now, my problem with using Castile soap has been the laborious preparation. They use "Kirk's" Castile soap in bars, which has to be dissolved in water and then mixed into your sprayer. Their procedure is to dissolve half a bar of Kirk's in a gallon of water and then mix one cup of that soap mixture into each gallon of spray mixture. For example, for five gallons of soap spray, you would use five cups of the Kirk's/water mixture.
After talking to Diane the other night and remembering that I didn't enjoy dissolving bars of soap in water, I "Googled" Castile soap to better understand it and here is what I found:
http://en.wikipedia.org/wiki/Castile_soap (which includes a picture of a bar of Kirk's).
I also found this story about making your own Castile insecticidal soap: http://www.ehow.com/how_5791479_use-dr_-bronners-insecticidal-soap.html
If you Google: "Castile soap insecticide" you will find several other articles, as well
I also found that Target sells Dr. Bronner's Castile soap in liquid form, so that means you don't have to dissolve bars of soap in water to use it. Here is the Target shopping site for Castile soap:
I enlarged the label of Dr. Bronner's Castile Soap and here are the ingredients: Organic coconut and olive oils, organic hemp oil, organic jojoba oil, lavandin extract, organic lavender oil, citric acid, and vitamin E. Now that sounds like something I wouldn't mind spraying on my roses and, if I happen to get some on me, I'll just lather up and wash it off!
I believe that adding baking soda to the Castile soap mixture at a rate of 3 TBP per gallon would probably make it a better fungicide, as well.
You could also substitute 2 TBP of Castile soap for the dishwashing detergent in the cider vinegar/aspirin, soap mixture I recommended in my last post: http://jack-rosarian.blogspot.com/2013/02/hazardous-roses-3-spray-nothing-toxic.html .
As soon as this year's new growth starts around here, I plan on spraying a Castile soap mixture early-on, and I'll let you know how it works.
Jack Falker (email@example.com)