This is a tough one to answer without knowing exactly what caused your original problem. It sounds like you eliminated many factors such as INSV. However, I've had some problems myself over the last 2 years that seem to track back to these factors:
1. Using exclusively RO water has given problems with pH shifts (too acid in pots as peat moss decomposes) and micronutrient problems. These have been addressed by using a mixture of city water (treated to remove chloramines) that has a higher pH and keeps the total pH in the pots more just slightly acid. Mixing my fertilizers up a bit and using no urea fertilizers seems to help too.
2. Spider mites or some other problems that I can't "see". I've been treating with Neem oil mixed with pyrethens (spelling) and that seems to have brought many suffering plants back. I've never been able to actually see a pest or webbing etc., but the symptoms and the results are sure similar.
A total sterilization would involve wiping all growing surfaces, pots and tools down with 10% bleach (or other sterilizing solution). I'd repeat at 5 day intervals for 2-3 weeks. That should take care of most pathogens. However, viruses (if that was indeed your problem) can survive for VERY long periods of time. You would want a 4-6 month break between plants to try to take them out.
When you do start back up, start small and keep watching for problems. I'm more inclined to think it was environmental factors or something that the folks missed if they were only looking for viruses (e.g. did they check for mites?).
--- In email@example.com, Dena Brent <kenyaviolet@...> wrote:
> As a long-time violet grower and one of the orginal members of AVI, I was stumped when my violets began having strange mottling and discoloration on the leaves. Having lived through cyclamen mites, root rot and other plagues I thought I had seen "everything".
> I was getting ready for a show- and had some pretty good contenders- and noticed that those violets were beginning to have the mottling. Could it be... a virus? The local extension agent sent it off for testing- no INSV or other related viruses. "Oh, it must be environmental". HMM. So I did all I could to change environmental factors- repotted, changed fertilizer, used RO water- but even young violets were getting the mottling. Sent off another violet for testing- again, NO for INSV and related viruses. Faced with sending it off a thrid time, the agent's advice was to dispose of my collection, sterilize and start again.
> So- I dumped over 200 violets- all infected with "mystery virus". I am in the process of washing down the plant room.
> My question is how long do I need to wait before I start again? The agent said- clean it up and start. However, I have heard of others who wait a year- or even two. What do you say?
> Thanks for your help
> Dena Brent
> Los Alamos, New Mexico
> (formerly Nairobi, Kenya)
> From: jsmith42001av <jsmith4@...>
> To: firstname.lastname@example.org
> Sent: Wednesday, September 21, 2011 1:18 PM
> Subject: AVC Looking for questions
> I've been bumped from this list for a while, but it looks like I've gotten back on.
> I'm working on my next hybridizing column for the AVM and could use a wider choice of questions. If you have something to ask, here's your chance.
> Jeff Smith