You test plants every three years? Even if you test new plants before bringing them into general population? Do you have new positives? Where do you think the infection comes from if new plants are virus free?
The first time I decided to test my entire collection I found 2-3 plants. Since then I have not found any retesting older plants in the collection. However, I was careful to test all incoming plants, specifically screening plants from older collections or divisions from vendors and always from auctions. I have had many positives for new plants even in plants from other growers who test and cull positive plants.
I was warned that sometimes there is not enough virus load in the plant to get flagged during the test. Sometimes the test itself fails, some test strips don’t run correctly. You can pick up virus when allowing plants to go to shows or meetings, being handled by multiple people, cleaned up by members not washing hands between plants, packed close and stored for transport, pulled for judging. Coming into contact with other virused plants or tables / stands, unwashed cloth, old wire used for name tags. Old pots that have not been completely sanitized, old metal stakes.
Often times I don’t test all the seedlings from a compot, I’ll only test one. Sometimes I don’t test individual seedlings from larger well know vendors who I know test. Other times I’ll run out of tests and will have to wait until I have the time and finances to purchase more tests.. around $5.75 was the cost of each test last I checked.
I do the best I can and I think it really depends on how many plants you have coming in and out of your collection. I’ll keep you posted if I find any positives this round. It’s been 4 years since I last tested everything.. I’ll probably finish up the majority of testing this fall / winter when I start repotting the phrags and have more time on my hands.
my position on this is a personal choice, I’m just putting this up here for your information. Whatever others chose to do with their own plants is their own personal choice and I respect their space and decisions.