Do you know if there's a difference between Zerotol for pro's and the Zerotol RST?

Just the concentration of the as-shipped product.

Zero-tol in the 2.5 gallon (smallest) container is 27% active ingredients, which being oxidizers, makes it a DOT hazardous material for shipping. The RTS (Ready To Spray) quart bottle is 6.7%, making it non-hazardous.

The application concentration would be the same, so when I refill the RTS bottle from my big jug, I make a 25% solution to use in the 150:1 RTS sprayer.

Thanks for the explanation Ray..... I'll be on the look out.

Remember, many orchids do not grow in the ground but on trees or rocks and their roots are adapted to having plenty of air flow. If you are having fungus problems, perhaps using a more open mixture (large lava rock) and net pots or baskets would help. This helps provide humidity around the roots without providing the conditions in which fungus can grow. Black roots could also be a sign of 'toxicity' to something in the water or too much fertilizer as others have mentioned. If you've corrected things concerning the water, the problem will go away once the offending substance is diminished enough in the medium. Changing or flushing the medium well with pure water will help if this is the culprit. Good luck!
Leafmite

Reporting back:
Looks good so far. I started with a couple that had been badly sunburned and I figured they were pretty much goners anyway. Well, they are not only still alive, they look like they are starting to recover. I've sprayed several since and so far no sudden deaths. I don't know if it is the fungicide or that it's been insanely dry but I haven't seen any new black root tips.

While I appreciate that 99% of root problems are actually medium and pot problems, most of the roots I am seeing this on are not in medium or pots. Most of my plants are mounted or in baskets and none have been in their current situation longer than 7 months. I have included a picture so you can see what it looks like. Sorry I didn't post it sooner, life can sometimes be too "interesting" to follow up on things like hobbies.

http://i68.photobucket.com/albums/i1...ds/aroots3.jpg

http://i68.photobucket.com/albums/i1...ds/aroots2.jpg

http://i68.photobucket.com/albums/i1...ds/aroots1.jpg

They look great. Whatever you have been doing it is working!

Fungicides safe for orchids.
 

I have used chlorothalonil on orchids including Dendrobiums with no ill effects. Some people will be familiar with this material under the brand name Daconil. It can also be found under many other names including "Ortho Garden Disease Control".

People here routinely report using mancozeb also known as Dithane and many other names and I used this on all my plants a few weeks ago with no ill effects.

People here also use Thiomyl also known as thiophanate methyl. It is a systemic so I have just bought some of it.

Both Mancozeb and Thiomyl can be purchased on the internet in small quantities.

Mancozeb and Thiomyl are often used as a mix to give a broader spectrum of activity.

Thiomyl is also one of the 2 fungicides in Banrot.

I read this thread with interest since I believe hobbyist use way too much fungicide most of which do nothing.

Your last photo was the proof. You have a normally growing orchid and the tips of the roots turn black when they stop growing from a variety of reasons.

I your case it is the method in which you potted in a basket with sphagnum. All the moisture is around the basket and the roots in the air are not receiving enough water to continue growing. The moisture is around the basket and the plant finds it easier to get the water there. That is the reason for all the new roots closer to the basket.

This is very noticeable on Vanda.

It is a natural growth pattern and you would have been fine doing nothing. All the fungal products mentioned here are bad poisons and should be avoided whenever possible.

Can I ask what products you prefer?

I think that what Jerry is saying is that he believes that hobbyists often use fungicides when they are not needed (and thus the fungicides do nothing).