I have them all together, and have for years, as did my mother, for many, many years, and she never lost one lily. I would have do say this is an old wives tale.

Blessings, Tina

There is some kind of virus that effects some of the other lilies and doesn't bother the tigers. I don't remember the name. Maybe somebody else can chime in.

That said I've grown Tigers and asiatics and orientals all together for ages.

As mentioned by Suenh, Tiger lilies are resistant to most lily virus, such as TBV and the cucumber Mosiac Virus. However, they can still host the virus inside them and this virus can be spread by gardening tools (cutting flowers on both lilies, one after the other) or by insects (primarily aphids). If you have an asiatic lily with virus it typically displays symptoms which allow you to cull it. However, with tiger lilies, you may not know that it has virus since it does not display any symptoms and the only hint may be lilies gradually getting infected and dying around it (or near it).

That being said, I grow tiger lilies and have not had a problem. I am rather virgillant about aphid control and I dip tools in a bucket with 10% bleach solution (9 parts water to 1 part bleach) between each cut when I deadhead flowers.

Just because you have not had problems, does not mean it can not become a problem in future, and having a "trojan horse" in a garden could eventually become a problem, especially if you are a lily collector.

If you are a casual gardener, it is certainly worth the risk because with some regular sound care you can keep all lilies happily growing and if you have a really bad year, worst case replant some lilies (including the tiger lily).

Personally, I hate to get rid of them because they are so pretty and it goes against everything I believe it when you get rid of the lily which is virus resistant to protect the lilies that are susceptible for virus infection.