Around the world, thoughts will differ as to what is considered a weed, as Richard correctly mentioned climate conditions. In the UK, there are a few Salvias which can seed around to become a nuisance, ONLY if one cannot be bothered to rake the seedlings out if they are unwanted. Here, these would include S. reflexa, S. tiliifolia, S. riparia, S. verbenacea, S. rypara, S. coccinea, and now S. subrotunda. But they really are not a problem, you just need a few minutes to rake them up. Urica, sclarea, amarissima, meyeri (which might now be S.rhinosina!!!),and scabra also seed around, but they are no problem. The biggest problem I have had here recently is not a Salvia, it is the beautiful Nicotiana mutabilis, whose seedlings can become a nightmare! But again, they are controllable, just! There is also a large Impatiens (I think it is glandulifera) with exploding seed-heads which can be very invasive and rapidly colonise a large area.

But in the UK, Salvias are not a problem. If we had frost-free winters, which we don't, then I would suggest that S. scutellarioides and S. macrophylla would be serious problems. Amazing that some of those mentioned on the list that Richard linked could be considered to be weeds! Salvia aurea????? No way!

I have heard that S. madrensis and S. guaranitica and S. atrocyanea can grow completely out of control, but then, maybe I should be grateful that we do have frosts here?

Kind regards to all...........Robin.

Some of Robin's comments (about the Nicotiana and Impatiens) bring out a point that I probably should have made in the original post.

Salvia enthusiasts and other plantspersons need to work with government agencies to help control weeds for our own benefit. They need us for our expertise to determine the level of risk that potentially weedy species present in all the different climatic zones we try them in. We don't want a ham-fisted one-size-fits-all argument from ignorance approach applied to our efforts. By demonstrating cooperation and maturity in working with them, we can enable both our interest in trying new species and their interest in preventing nasty plants from escaping. We need each other.

Right now NARGS (North American Rock Garden Society) is cooperating with APHIS on regulations for the import of seed into the USA. Here is a quote from a post on Alpine-L from Joyce Fingerut of NARGS:

"When our extended group protested the phyto requirements for seeds, and commented on the proposed regulation, we apparently gained a good name with the Agency for civility and reasonableness. I received positive comments from their staff members. I fully expect that this will continue through the upcoming discussion."

The discussion she referred to is a period for email posts to APHIS. The APHIS announcement says that the topic is how to define invasive plants.

On November 27, 2006 a link to the discussion will be posted on this website:
http://www.aphis.usda.gov/ppq/Q37/revision.html

Here is a link that might be useful: APHIS weed control discussion site (definition of weedy species)

I imagine any seeded plant could become a pest if all conditions are ideal AND there are not it's natural nemeses to keep it in line. But then, one must remember someone's definition of a weed as: any plant that tries to exist where it isn't wanted.
Of course, then, there are the plants that have totally gotten out of control and are ruining natural environments. And, I'm sure this is what you're talking about. I just can't imagine a Salvia becoming such.

There is at least one which has become a major pest in the western USA: Salvia aethiopis. Over large areas of the west, it does not need disturbed sites to spread. Salvia sclarea will spread in disturbed sites, and in at least two locales, in undisturbed areas. One is in Idaho, and the other in a range in California.

I would be concerned about S. lyrata in the Pacific states. Colonies are thickening in the eastern states, and it is considered a lawn weed here. Lots of others are weedy, like S. reflexa, found in barnyards.

The ag departments in Oregon and Washington are very concerned about meadow sages (S. pratensis, S. nemerosa, etc)

WOW! I didn't know, Rich.

We have the following Salvia's listed in our WA State Class A Noxious Weed list: S. pretensis (Clary/Meadow Sage), S. sclarea and S. aethiopi.
In the US no native plant can be classified as noxious; only those that are non-native can be considered. The criteria for classification considers plants/weeds which cause economic/ enviromental/human harm to any given ecosystem. I believe that is the way it works in all countries.

Vera