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  • 3 Post By chemist
  • 1 Post By naokit
  • 1 Post By raybark

Physan 20

This is a discussion on Physan 20 within the General Orchid Culture forums, part of the Orchid Culture category; For those of you that use Physan 20 what concentration do you use and do ...

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  1. #1
    grubea's Avatar
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    Default Physan 20

    For those of you that use Physan 20 what concentration do you use and do you treat on a regular basis? If so how often?

    thanks
    Aaron

  2. #2
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    Physan is a contact algicide/virucide/bactericide/fungicide. Use it only if there any sign of any of these. I don't use physan as we don't get it here but I have read it to be used at 2 teaspoon to a gallon

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    I have used it for orchids with problems with spotting on their leaves, seems pretty effective as preventing new damage. I just used it at the concentration on the bottle, sorry I don't remember atm what that is and don't have it handy. I haven't been using it regularly, mostly because I just forget I should for some of my plants. However, even not too often seems to help them quite a bit.

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    here is pic of Physan 20 insert for orchid application
    Name:  physan20.jpg
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    Name:  physan20_1.jpg
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    Default

    Thanks guys for the quick responses.

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    Chemist is right on the spot with those pics. 1 tsp/gal mix as a preventive. I use it regularly along with my fertilize, it helps algae from building up on my pump sprayer. ---- Vendor information removed - see FAQs on Posting ---- It's a good idea to pre-soak you media in a physan/water mix when repotting.

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    Physan's tech info used to have a document saying: "PHYSAN generally is not phytotoxic to plants at concentrations below 400 ppm. However, this can vary depending on the type of plant and its stage of growth." I can't quite relocate the link. 400ppm is 0.5TBS (or 1.4tsp) per gallon, I believe. But a bad combination of timing/environment seems to cause some minor injury (like bleaching) for some plants. It is supposed to be effective killing bush snails at 200-400ppm, so I had to drench my orchids recently. Out of 300-400 orchids, about 3 showed a bit of bleaching. So it is pretty safe. There are several ways to approach orchid culture, and some people promote the "preventative spraying". But more recently, people seem to be moving toward valuing the associated microbes. Inside of the pots, there are some microbe fauna, and maintaining good fauna helps with the plant help. Even under cultivation, mycorrhizae can develop inside of the pots. Also there are fungi like Trichoderma (root shield, which is parasitic fungi against some pathogenic fungi) or effective microbes (EM-1, Inocucor), which may or may not help orchids. Some algae (actually cyanobacteria) can fix nitrogen, so it could provide additional nutrients (it might be at a smaller scale compared with chemical fertilization, though). These are still hypothetical ideas (i.e., I haven't seen strong scientific evidence in ORCHIDS), but I tried not to use broad-target chemical control. If orchids are developing diseases frequently, maybe some other factors are not right (e.g. plants are stressed due to low humidity, not sufficient light etc).

    Another use of physan 20 is to kill cells near the infected region. When you catch some bacterial infection at an early stage (e.g. 3-5mm), you can use cotton swab to apply undiluted physan 20. Then you can use a needle (heat sterilize) to poke holes around the infected regions (so Physan can penetrate). I start from the healthy outside region toward the infected inside region (so you don't spread the disease to nearby region). It generally kills the cells and become brown quickly, and the bacteria can't spread anymore. As one of the methods which plants uses to fight against pathogen is to self-destruct the infected cells. So this is kind of imitating the process. In this way, you don't have to chop off the entire leaves. If infection is too progressed, this doesn't work.

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    Naoki is correct to warn about some plants' sensitivity to the stuff. I gave up using it about 5-6 years ago, but the "word on the street" is that "thin-leaved species" and some dendrobiums are particularly sensitive to the stuff.

    I replaced it with what's now known as BioSafe Disease Control (also sold as Zero-Tol and OxiDate), which is a stabilized hydrogen peroxide product that has shown zero phytotoxicity. Interestingly enough, even though it's got a fraction of the amount of peroxide in it that a bottle from the drug store has, it is far more effective of a disinfectant. Drugstore peroxide decomposes almost instantly, leaving a puddle of water behind. The BioSafe products stay active as long as they are still liquid.

    About 2-3 years ago, I stopped using it as a preventive (thank you, Flordeloto, for knowing the word is not "preventative"), and switched to the regular application of a biological product, Inocucor Garden Solution, which uses beneficial bacteria and fungi to kill pathogenic ones, and lives both within the medium and plants themselves to prevent such diseases.

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