Tomatoville® Gardening Forums - View Single Post - Disease Control (fung-onil vs Oxidate vs Serenade)

greentiger87 · September 11, 2012

I've seen a lot of references to using improved hydrogen peroxide formulations as post harvest washes, mostly to avoid the safety issues and irritancy of chlorine gas or bleach (usually calcium hypochlorite).

I wish there was some data available comparing the phytoxicity of bleach to something like Oxidate. In theory, oxidate should be better at killing spores than bleach.. but we've seen great testimony as to the effectiveness of bleach. The only complaints about it seem to be that it can damage leaves. Maybe the only reason it's not used more often is that its not registered for use on crops?

I also wonder how much of that damage is due to the high pH of common bleach. For germicidal applications, *already diluted* bleach is acidified to a pH of around neutral, which makes it much more effective in killing microorganisms and spores. This isn't widely bandied around because adding an acid directly to concentrated bleach results in the production of chlorine gas, which can be deadly (as hopefully everyone has heard by now). But when the pH is around 7, you can use much less bleach for the same killing effect.. meaning less potentially phytotoxic salt residue on the leaves.

So the question is, what aspects of the bleach solution or hydrogen peroxide solution are important to controlling the plant diseases, and which of these factors causes damage to the leaves?

1) strength of the oxidizer? hydrogen peroxide and peracetic acid win here, but bleach isn't significantly behind
2) speed of the oxidizer? peracetic acid definitely wins, but bleach isn't significantly behind
3) pH of the solution? bleach solutions are normally high pH, but can be lowered to neutral. Peracetic acid solutions will be low pH. Hydrogen Peroxide solutions are usually near neutral, but can be lowered. Normal rain has a pH of about 5. Though I've only just started using bleach, I acidified it with vinegar and have yet to see any damage.
4) surfactant choice? soaps, insecticidal or dish, will be better at killing, but will also be more phytotoxic. Non-ionic surfactants are less phytotoxic.

September 11, 2012	#28
greentiger87 Tomatovillian™ Join Date: Aug 2012 Location: Houston, TX - 9a Posts: 211	I've seen a lot of references to using improved hydrogen peroxide formulations as post harvest washes, mostly to avoid the safety issues and irritancy of chlorine gas or bleach (usually calcium hypochlorite). I wish there was some data available comparing the phytoxicity of bleach to something like Oxidate. In theory, oxidate should be better at killing spores than bleach.. but we've seen great testimony as to the effectiveness of bleach. The only complaints about it seem to be that it can damage leaves. Maybe the only reason it's not used more often is that its not registered for use on crops? I also wonder how much of that damage is due to the high pH of common bleach. For germicidal applications, already diluted bleach is acidified to a pH of around neutral, which makes it much more effective in killing microorganisms and spores. This isn't widely bandied around because adding an acid directly to concentrated bleach results in the production of chlorine gas, which can be deadly (as hopefully everyone has heard by now). But when the pH is around 7, you can use much less bleach for the same killing effect.. meaning less potentially phytotoxic salt residue on the leaves. So the question is, what aspects of the bleach solution or hydrogen peroxide solution are important to controlling the plant diseases, and which of these factors causes damage to the leaves? 1) strength of the oxidizer? hydrogen peroxide and peracetic acid win here, but bleach isn't significantly behind 2) speed of the oxidizer? peracetic acid definitely wins, but bleach isn't significantly behind 3) pH of the solution? bleach solutions are normally high pH, but can be lowered to neutral. Peracetic acid solutions will be low pH. Hydrogen Peroxide solutions are usually near neutral, but can be lowered. Normal rain has a pH of about 5. Though I've only just started using bleach, I acidified it with vinegar and have yet to see any damage. 4) surfactant choice? soaps, insecticidal or dish, will be better at killing, but will also be more phytotoxic. Non-ionic surfactants are less phytotoxic. Last edited by greentiger87; September 11, 2012 at 12:14 PM.