Never give up! I say this as I was on the point of giving up this year, the hottest and driest Summer since 1976.........and I remember that well!!! Spidermite thrived in our hot and dry conditions, spent a fortune on the predatory mites, these worked on most Salvias (Dahlias also), but not all. These blighters have just about killed the following Salvias......concolor, graciliramulosa, rubescens, dombeyi, gachantivana, and also badly affected splendens, Theresia and hybrids, miniata, curviflora, and even coccinea! So depressing after such hard work gardening in spring. Also, the unbroken hot sunshine for 2 months here (not since 1976!) has caused many plants, not only Salvias, to abort the flowering buds. But I have a wonderful sun-tan!!!
But at last we have had rain, and things are picking up. Same for all Salvia collectors around the UK. I have several visitors and an important group visiting my garden next month, hoping for more rain, but sunshine when they visit!
Kermit's advice is invaluable.
Bollocks to spidermite......kindest regards to you all!
Robin.