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Framingham, MA

Late yesterday afternoon I removed all the dead/dying leaves from powdery mildew and then sprayed both the underside and tops of the remaining good leaves - up to now, in my ignorance, I had just been spraying the top of the leaves. I noticed that my solution of 2 tablespoons of baking soda and 1/8 teaspoon of Dawn concentrate adheres well to the leaf tops but seems to roll right off the undersides of the leaves (the teflon effect). I think I have enough dish soap concentrate in the mix as when the sprayer is empty I still have a good amount of soap suds left.

My question is this: what can I add to the mix to get better adhesion to the leaf underside? Neem Oil?

9/24/2005 8:13:23 AM

Ontario, Canada.

I have used Horticultural oil regularly this year. From most of the studies I have read it is best surfactant to use with baking soda.

"Some of the work at Cornell has focused on controlling fungal diseases on cucurbits.(4) A single spray application (to runoff) of 0.5% (wt./vol. of water) baking soda, plus 0.5% (vol./vol. of water) SunSpray UFP® horticultural oil almost completely inhibited PM on heavily infected pumpkin foliage. Baking soda without spray oil was ineffective, and a 2% (wt./vol. of water) solution of baking soda damaged the leaves."

http://attra.ncat.org/attra-pub/bakingsoda.html

9/26/2005 5:15:24 PM

Ontario, Canada.

An article in the February, 1996 issue of GrowerTalks magazine follows up on the continuing research at Cornell. Testing with a variety of bicarbonates revealed that selecting the correct bicarbonate for a particular disease is important. Dr. Horst's research team found that ammonium bicarbonate had the strongest effect on some diseases, while potassium and sodium bicarbonates worked best against others. Potassium bicarbonate provided the best control of PM. "Sodium bicarbonate is okay, but it's not as good," Horst is quoted as saying. "And ammonium bicarbonate doesn't do the job on powdery mildew."

He points out that while conventional chemical controls for PM are preventatives only, bicarbonates can eliminate the disease after it has already appeared on certain crops—

9/26/2005 5:17:06 PM

Ontario, Canada.

J. Howard Garrett—a well-known horticultural columnist and radio personality in the Dallas, Texas, area—recommends baking soda sprays at a concentration of 4 teaspoons per gallon of water for control of PM, blackspot, brown patch, and other fungal diseases. He also suggests that a light soil spray of baking soda solution can suppress fungus gnat problems, while cautioning that overuse should be avoided because of possible negative effects (sodium accumulation and alkaline pH) on the soil.(28)
The authors of an organic pest control handbook suggest the same concentration mixture as Garrett, but advise the addition of an equal quantity of liquid dish soap or insecticidal soap as a surfactant.(29)
The P. Allen Smith Gardens website advises mixing 1 heaping tablespoon of baking soda, 1 tablespoon of dormant oil, and ½ teaspoon of insecticidal or dish soap in one gallon of water as a PM spray. Stating that plants should be well hydrated prior to spraying, this source recommends irrigating a couple days in advance.(30)

9/26/2005 5:19:53 PM

Ontario, Canada.

References
1. Williams, Greg and Pat Williams. 1993. Baking soda vs. powdery mildew: Not a new idea! HortIdeas. June. p. 62.

2. Williams, Greg and Pat Williams. 1985. Baking soda for powdery mildew control. HortIdeas. September. p. 101-102.

3. Anon. 1990. Baking soda can ward off fungus. Greenhouse Manager. June. p. 24.

4. Ziv, O. and T. A. Zitter. 1992. Effects of bicarbonates and film-forming polymers on cucurbit foliar diseases. Plant Disease. Vol. 26, No. 5. p. 513-517.

5. Williams, Greg and Pat Williams. 1992. More on baking soda/horticultural oil vs. fungal disease. HortIdeas. June. p. 69.

6. Hofstetter, Bob. 1993. Homemade pesticides. The New Farm. February. p. 14-16.

7. Moore, Sallyann Roberts. 1996. Bicarbonates offer effective disease control. Grower Talks. February. p. 72.

8. Ziv, O. and A. Hagiladi. 1993. Controlling powdery mildew in euonymus with polymer coatings and bicarbonate solutions. HortScience. Vol. 28, No. 2. p. 124-126.

9. Williams, Greg and Pat Williams. 1993. Baking soda and horticultural oil vs. powdery mildew. HortIdeas. May. p. 51.

10. Byczynski, Lynn. 1995. New ideas for a new year. Growing for Market. January. p. 1, 4-5.

11. Williams, Greg and Pat Williams. 1997. Sodium bicarbonate for control of mildew on grapes. HortIdeas. June. p. 70.

12. Otten, Paul. 1997. Can kitchen products control powdery mildew? Northland Berry News. Fall. p. 20.

13. Elmer, Wade H. and Frank J. Farandino. 1997. Managing powdery mildew of cucurbits. The Natural Farmer. Summer. p. 26-27.

9/26/2005 5:21:54 PM

Framingham, MA

Kahuna3, thanks for all the info and the references. I can see I have some reading to do. Next year I will give the horticultural oil a try on the undersides of the leaves.

9/26/2005 6:10:00 PM

Montoursville, PA

Neam Oil gives the same support and carrys with it a natural insecticide, miticide and fungicide. Cut or do not use the soap with Neam Oil but the Baking Soda is OK and makes it even better.

9/26/2005 8:12:54 PM

Framingham, MA

Doc, I have a small bottle of Dyna-Gro Pure Neem Oil and the directions say "Mix 1/2 teaspoon per quart of water (1 oz. per gallon), plus 1/4 teaspoon of liquid dish soap per quart of water (1 teaspoon per gallon) as an emulsifier. Shake well." Don't I need the soap to bind the Neem Oil to the water?

Also, since my wife buys Dawn Concentrate I use about 1/8 teaspoon per 1.25 gallons of water since that still leaves some soap bubbles at the bottom of the sprayer bucket when it is empty. It rained here last night so this afternoon I will try adding Neem Oil to my mix to see if that gives me better adhesion to the underside of the leaves.

9/27/2005 8:12:46 AM