Kal2002:
Where do you garden in? Soil Type etc would be helpful too.
Any insect activity? as they can transmit diseases that can cause some of these problems We will look forward to hearing from you.I have had some problems w/ S.greggii and microphylla
with these same symptoms. One thing I did was to remove any dead wood cleaning the prunners in between cuts so not to spread it to other plants or branches.My S greggii "Lipstick" survived and has not had any problems to date.
We will look forward to our reply.
Art

Don't forget to include whether or not you have it in a low place and how much rain/snow you have had.

Greggiis and microphyllas can strangle themselves when they get big. There is too much vascular system on old wood to channel water through, and too little nutrient to absorb through old roots. That's why they have evolved to layer themselves to provide a new crown to send roots and stems from. This works better in soils with good drainage.

I looked at the plant again yesterday evening. I was going to cut off the branches that have the wilted leaves and flowers but I noticed that new leaves are growing from the same branches as if to replace the wilted ones so I left them alone. I did prune parts of the branches that are dead and dried up.

This salvia is planted in a flower bed next to Salvia Cherry in regular soil covered with bark. It is not in a low place. I planted them there 2 years ago and never had any problems. The problem did not affect the Salvia Cherry, just this plant. I live in northern California. We have had very wet weather this past winter and then warm days and cold nights lately. The temperature here was in the low 30's during the winter for a few nights but it did not affect these plants back then. Maybe the few warm days we had lately and the sudden cold nights, down to the low 30'a again, did have some effect. The plant acted like it was frost-bit but we did not have frost. It only got down to about 34 degrees.

Anyway, I am watching it closely now to see what happens next. I will keep you guys posted.

I am in Redding , Northern Cal also. The same thing happened to me in late spring of last year with a pink Greggii that I had had for two years. One major branch died which I cut off at ground level , followed by another about two weeks later . About 6 weeks later the plant threw new growth from the base and has looked fantastic ever since . I get this same thing happening on Escolonia and Indian Hawthorne . Maybe its oak root fungus .

I finally decided to trim back some of the branches with the wilting leaves and flowers. Even the new growths from those branches have wilting leaves and the flowers are smaller than normal. The new leaves also curl at the edges. After I cut a branch, I noticed that the middle part of the branch did not look solid. I poked at it with a toothpick and it is hollow even though it is white. I wonder what that means?

Wild Watermelon should have solid wood. It sounds like you have some kind of stem borer, usually associated with wilting and sudden die-off of cucurbits, including squashes.

Follow the hollowness back, and you may find a point where the larva bored a hole in the stem, and a tiny patch of sawdust near the hole.

I've occasionally seen a borer on Salvias, but these are usually the fast-growing tropical sages.