We have some problems in the UK, the worst being red spider-mite. This is a particular problem with S. dombeyi, S. concolor, Van Houttei, and the large Splendens. Regular and frequent sprays of water on the underside of the foliage can help, also good air circulation which is not easy in a crowded greenhouse!

Aphids.....whitefly, greenfly, and blackfly attack some plants, but these can be spotted more easily, and a gentle spray of strongly diluted washing-up liquid usually works. The Salvias which seem to me most affected are Indigo Spires, gesneriiflora, tubiflora, carduacea, and farinacea.

Outside, I sometimes get die-back on S. fulgens and S. patens, probably a virus. I just cut off the dieing stems.

Weather conditions play an important part. No two English summers are the same, and some Salvias can behave very differently each year.

Robin.

Art

Ive not had any diseases but I have had aphids attack. One year aphids nearly destroyed a sal. subrotunda and I was about ready to yank it out , then I saw one lone ladybug on the plant getting busy gorging herself so I let it be for a few days. LB stayed there untill the plant was completely clean and that plant turned out to be the biggest and best plant in my garden. Since you brought it up I thought Id relate that good story.

Robin & Hummersteve Thank you for the feed back:
here is my list:
outside conditions:
1)Aphids,Whitefly & Mealy bugs- S.guarntica and hybrids- Insecticidal soap
2)Rust (Puccinia) Salvia coccinea,S.microphylla -
Daconil fungicide
3) Tobacco Mosiac Virus -Salvia azurea var. grandiflora-
Destroy plants/workers wash hands before repotting.
Greenhouse conditions:
all the above
Downy Mildew-Red Salvia greggii-Destroy plants-prevent with fungicide
Botrytis-S.splendens(empire series)-Corynespora Stem Rot and leaf spot Don't grow this series anymore
Powdery Mildew- S.farinacea -1part milk/10parts water
clears this right up.
Good horticultural practices seem to prevent these disease
which I have not has a problem with do to our drought.
Art