Fungicide Burn: RD-20

[LJA]

We've received several emails now asking whether RD-20 is safe to use on orchid plants, so I thought I'd post something about it here. RD-20 is marketed commercially as a bactericide / fungicide for orchids and, when used as directed, does a fine job.

HOWEVER: Even when dilluted and used as directed, RD-20 will burn many orchid blooms, causing them to turn brown where the solution has contacted the flower. Use RD-20 ONLY on your non-blooming orchid plants and be sure not to mix the solution any stronger than 1 tablespoon per gallon of water.

If you don't mind a little white haze residue on your orchid's leaves, Daconil fungicide, also readily available, does a fine job as well and doesn't burn the blooms. And if you're having problems with bacterial infections, plain old Listerine mouthwash will work wonders.

[lupita]

Hello.
I grow my cattleyas in a greenhouse in Albany, Ga. using rain water and reverse osmosis. can I use rd20 with this type of water ? I was told to mix rd20 and tap water. also can I mix it with a 20-20-20 and bloom boster ? Is rd20 sysmetic ?.
Thank you.
Lupita.

[Brutal_Dreamer]

Hi Lupita,

I see no problem mixing RD-20 with rain water and reverse osmosis. I would not plan to water with it though. RD-20 is a topical solution. It is not systemic. Mix your fertilizer and bloom booster and water with your regular water (rain water and RO). Spray on the RD-20 as a bactericide / fungicide for your orchids.

Welcome to the forum!

Cheers,
BD

[shmaz]

You mentioned using listerine as a bactericide. I've not heard this before so am unfamiliar with the general directions for use. Is it recommended you dilute the listerine or use it full strength? Is it effective on both phals and cattleyas?

[Brutal_Dreamer]

You mentioned using listerine as a bactericide. I've not heard this before so am unfamiliar with the general directions for use. Is it recommended you dilute the listerine or use it full strength? Is it effective on both phals and cattleyas?

Use it full strength. It will work on both cattleyas and phals. Welcome to the site!

Cheers,
BD

[lupita]

Hello.
Is there any way I can attach a picture to get an idea what is wrong with it ?
Thank you.

[Brutal_Dreamer]

Hello.
Is there any way I can attach a picture to get an idea what is wrong with it ?
Thank you.

Sure, see this thread: How to post a photo.

Cheers,
BD

[Bikerdoc5968]

The last thing I'd do is "step" on someone's toes! So.... RD-20 is now SA-20 made by Southern Agricultural Insecticides, Inc. I guess they changed the name to be more in line with the company name???????? Anyway, it is EXACTLY the same formulation as its cousin Physan 20 and used EXACTLY the same way. The company that markets Physan 20 is on the west coast, Maril Products Inc. During the summer, I hang my phals outside from my deck overhang and because they are under a large oak tree, I spray them and the flowers frequently (couple of times a month) because of the mildewv problem from the tree. I'm not completely convinced that it is the chemical that causes the spots but just water on the flowers. I say this because listed in the product instructions for use is the following:

"Botrytis Petal Blight: During cool weather, spray plants, flowers and under benches at first sign of spotting on flowers. Normally, weekly
sprayings will greatly reduce or eliminate the botrytis spotting. Use 1 tsp. of R-D-20 Greenhouse Disinfectant per 3 gallons of water."


It also goes on to say that the use as a preventative maintenance is:

"Adult Plants: Spray any time disease is evident with a solution of 2 tsp. R-D-20 Greenhouse Disinfectant per gallon of water. Spray once per
month as preventative maintenance"

Anyway, I post this not to start an argument or get anyone's nose out of joint. I use SA-20 on a regular basis as do many commercial grows who add it to their misting/watering system and have never had a problem. BUT, you MUST use it as directed for the use as: GREENHOUSE DISINFECTANT FOR ORCHIDS & ORNAMENTALS FOR USE AGAINST FUNGAL, BACTERIAL, ALGAL AND VIRAL PLANT PATHOGENS AND THEIR ODORS......
Greenhouse Disinfectant is a Concentrate and Must be Diluted Before Use

[orcoholic]

I use a product called ZeroTol. It's like a supercharged Hydrogen Peroxide and gets diluted oneoz/gal. Never had any problems at all on anything. Safe for pets, fish, etc. and does everything Physan and RD 20 do.

It comes in a large container 2.5 gal, but lasts in the original container.

[sirina]

Thanks for the advice, but since I am very new at growing orchids I need lots of advice. Can I spray it on the leaves and on the roots? I have a very sick cattleya and I do not want it do die. Please help me.

sirina