Disinfecting & Pre-treating Orchids

[Chlorophile]

I see many people use Physan 20 or hydrogen peroxide dilutions when repotting or cutting orchids. Is this something I need to be doing and should I be spraying down new orchids with something when I first bring them home? Currently I spray new houseplants with Neem Oil just in case. I don't really understand the difference between all the various disinfectants.

[estación seca]

Preventive disinfection of any plant or animal, including people, absent a known problem, is a bad idea. Unless there is a recognized bacterial or fungal problem, the disinfecting chemicals will not help, and may hurt.

As an example, the hydrogen peroxide you mentioned is a strong oxidizing agent. It can damage roots and very young shoots on orchids. If you don't believe this, put a small amount in your nose.

All living organisms support an extensive system of microorganisms, mostly beneficial. In animals it is on our skin and in our digestive tract. In plants it is all over the exterior of the plant.

Orchids in the wild have symbiotic fungi living inside the cells of the plant. Indeed, almost no orchid seeds in the wild would be able to sprout and grow without these endosymbionts.

These beneficial organisms, in many cases, prevent infection with pathogens. A generalized disinfectant, such as alcohol, physan 20, hydrogen peroxide or sodium hypochlorite (bleach) solution, will kill these beneficial organisms, potentially rendering the organism MORE susceptible to infection than if the disinfectant were not used.

Bacterial or fungal infection usually occurs in the setting of a plant unhealthy due to poor care, or poor growing conditions. Take good care of your plants and you will only rarely need to deal with these problems.

My hot, arid environment outside my growing area is not conducive to bacteria, nor fungi. My growing area has a relative humidity of around 60% maximum, often lower. I have not seen any bacterial, nor fungal infections in the last 3 years.

The widespread use of preventative antibiotics in farm animals is considered to be a major factor for the spread of drug-resistant bacteria to and in humans. The antibiotics are needed to keep the animals alive in extremely unhealthful environments, eating food that is bad for the animals.

The US Centers for Disease Control and Prevention (CDC) have changed their recommendations for hand soap. They no longer recommend disinfectants in hand soaps, as this probably promotes the spread of pathogenic organisms, by suppressing beneficial organisms on human skin. Bacteriologists doing research with skin organisms since the 1970s have recommended not using disinfectants for washing healthy skin, and it took the CDC 40 years to catch up.

[King_of_orchid_growing:)]

In most cases it is not necessary to disinfect an orchid prior to having it go into someone's collection. A healthy orchid is able to fight off pathogens without any additional help most of the times.

On to the chemicals in question...

Physan 20 should not be used on the orchid itself in my opinion. In my experience it has caused a lot more problems than any kind of good. In some cases some of the orchids I have treated with Physan 20 had died as a result of the damage it had done to the orchid's root system.

Here is the Material Safety Data Sheet on Physan 20:

http://www.physan.com/uploads/4/7/1/...san20_msds.pdf

Notice that the MSDS for Physan 20 states under First Aid Measures in the section Acute Health Effects that it:

"Causes corrosive burns. Brief exposures may cause irritation and defatting of the skin."

Cell membranes are made of phospholipids, (fatty molecules attached to a phosphorous molecule). Physan 20 apparently affects the lipid layers of cell membranes and that is probably the mode of action in killing microbial organisms.

Hydrogen peroxide should also not be used on the orchid itself. It is a strong oxidizer. When it is still active, and it comes into contact with cells, it causes damage to the cell membranes. It does so by stealing electrons. It causes a chain reaction to occur, and the effects have to be neutralized.

Here is information on hydrogen peroxide:

Free Radicals and Reactive Oxygen

The large majority of my collection have never been disinfected, and the ones that are strong have been with me for years.

I have disinfected orchids with fungicides before, but the ones that were weak always end up getting fungal infections that kills them off anyways despite the treatment.

Again, in my opinion, I don't think it is necessary to do that much work to disinfect the plants themselves. If you'd like to disinfect your work station, empty pottery, or your tools, that is fine.

This is going to sound cheesy, but if anybody was a fan of the 80's The Karate Kid movies, even Mr. Miyagi says: "Strong roots, strong plant."

The key to a strong plant had always been a healthy root system. Since an orchid is a plant, this applies to them. I have observed on many occasions that this is the case.

And also, yes, what ES had said about plants containing microorganisms on their external surfaces that keep each other in check is also true. In fact, every living organism has this going on.

---------- Post added at 08:12 AM ---------- Previous post was at 07:43 AM ----------

I edited my post above. I added more information as evidence against using these chemicals on the plants as disinfectants.

[Orchid Whisperer]

If you suspect a bacterial or fungal infection before you buy a plant, don't buy.

If you find such an infection right after you buy, decide if you either (a) want to take it back, or (b) want to try fixing it ("both b and c" is not a reasonable choice IMO unless you and the seller agree in advance of treatment).

I find the best treatment for many epiphytic orchids that have fungal or bacterial problems is to take away all medium and placing them in a shaded dry environment. Portions of leaves that have been damaged may need to be cut away, always using a very sharp blade or scissors and flame sterilizing between cuts. Dry conditions are less favorable for bacterial and fungal infections to spread. Then, focus on good plant care and hygiene, including providing calcium (I've posted like a hundred times on providing calcium, see the Orchidboard search function). I do own a couple systemic fungicides I bought a couple years ago but haven't used.

After stabilization of the plant and treatment, gradually resume good normal care.

[dounoharm]

I am a southern girl, and my mama was fixed on disinfecting EVERYTHING! every Saturday, it was time to clean with CLO-ROX on every painted surface and the wash, and on the floors, it was LYSOL or PINESOL, lol….

in my horticulture classes, everything was disinfected, pots tools whatever you used in a Clorox solution, or with physan 20...

I keep a physan solution in an old coffee can for my tools, and a bucket of Clorox solution for pots....after I empty a pot it gets a soak in Clorox, and when I use a tool it gets physan. its just the way I do things in the greenhouse....

I also use a solution of photon 27 2-3 times a year to wash my benches and anything else in the gh…

I don't like bugs and I don't like bacteria or fungal disease, and it is true...prevention is the best medicine!

[estación seca]

Originally Posted by dounoharm

I am a southern girl, and my mama was fixed on disinfecting EVERYTHING! every Saturday, it was time to clean with CLO-ROX on every painted surface and the wash, and on the floors, it was LYSOL or PINESOL, lol….

in my horticulture classes, everything was disinfected, pots tools whatever you used in a Clorox solution, or with physan 20...

I keep a physan solution in an old coffee can for my tools, and a bucket of Clorox solution for pots....after I empty a pot it gets a soak in Clorox, and when I use a tool it gets physan. its just the way I do things in the greenhouse....

I also use a solution of photon 27 2-3 times a year to wash my benches and anything else in the gh…

I don't like bugs and I don't like bacteria or fungal disease, and it is true...prevention is the best medicine!

Inanimate objects, yes. But disinfecting the plants without a known reason is neither necessary nor helpful.

[Chlorophile]

That all makes sense. I am assuming all of this disinfecting the actual plant has just become ingrained because most of the time the orchids aren't getting proper care and so get sick more often.

[estación seca]

A lot of people: (pretend to) disinfect and bug-spray everything in their environment, to the point of using harmful chemicals in their homes; take medicine when there is nothing wrong; take medicine when it won't work for the condition at hand; won't eat anything they saw a bug land on, no matter how it is prepared and cooked; and, in general, can't leave well enough alone.

We humans don't believe in anything we can't see; we think we have much more control over the environment than we do; and we engage in magical thinking all the time. If a little is good, a lot is better. Well, it probably can't hurt, and it might help. I know I shouldn't, but maybe it will turn out all right. My grandmother did this and lived to be 99.

[King_of_orchid_growing:)]

Originally Posted by Chlorophile

That all makes sense. I am assuming all of this disinfecting the actual plant has just become ingrained because most of the time the orchids aren't getting proper care and so get sick more often.

My assumption on a hobbyist's idea to disinfect plants (orchids) as a preventative measure is most likely due to the relatively poor knowledge we have on a plant's (orchid's) immune system and how it acts on the pathogens associated with these plants. As hobbyists, we simply do not have access to these kinds of resources unless a researcher has published their findings in a paper.

Many of us who have been educated in science properly are already aware of Germ Theory, (the theory first proposed by Girolamo Fracastoro and later empirically founded by Louis Pasteur and Robert Koch that states that diseases are caused by certain microbes that invade, metabolize, and reproduce within their living hosts), whether we know to call it this or not. It is clear that people who are disinfecting their plants as a preventative measure understand that there is microbial life that we cannot see with the unaided eye causing disease. Notice also how people are more aware of and attempting to identify, (whether accurately or inaccurately), the plant pathogens and even going as far as to mention their scientific names. This understanding also manifests itself in horticultural practices where tools, pottery, and work areas are disinfected prior to use.

What we seem to lack in understanding is how the plant deals with these pathogens physiologically. Notice how nobody in any orchid related forum you visit, (including me), do not and probably are not able to discuss with you in great detail how a plant's (orchid's) immune system really works.

The only things I have to offer in regards to plant immunology are that:

The leaves of plants normally produce a waxy cuticle layer on its surface. This is what gives the leaves their natural shine. This waxy cuticle layer is presumably the first line of defense against pathogens that land on the surface of the leaf.

I am aware that when a plant pathogen damages or kills cells on the plant, there is a response where the plant tries to isolate the pathogen to the area(s) of infection by programming cell death around the area, (apoptosis). This is why you get those funny halo like rings on the plant's leaves during a fungal attack.

I know that plants produce phytochemicals to ward off insects that feed on them and attract other insects that may predate on the insects that feed on the plants in order to achieve control and balance.

I also know that plants have the ability to communicate with one another by chemical means to warn others in the community of animals that may predate on them or indicate that there are foreign invasive plants that threaten their livelihood or community.

There are videos dedicated to plant communication all over the internet, (including places like YouTube).

Aside from this, I don't know much about a plant's immune system. I'm not able to describe in detail how a plant's immune system deals with these pathogens physiologically the same way I could tell you how a human being's immune system works. I also haven't been able to find much in terms of scientific articles relating to plant immunology. Most community colleges here in Southern California, (Los Angeles County), do not offer any in depth botanical studies other than the basic introductory course to botany. Whether public or private universities offer classes on plant immunology is questionable. It has only been through repeated observations of multiple individuals within a species and through multiple species that the pattern emerges where an ailing plant usually has an unhealthy root system. There is something about the roots on a plant that is linked to their immunity as well as their physical well-being, I just don't know what that connection is.

The only thing I do know is that it has been proposed that somewhere along the plant's growing root tip is the area where the plant seems to operate much like our brain does. There are papers documenting this you can search.

[Orchid Whisperer]

I like corn