Here are my thoughts:

White fungus in the soil is not necessarily a problem. Healthy soil is alive with fungi and bacteria--they indicate the soil is active. I would not worry about that. If you were somewhere that is constantly damp and soggy fungus might be a problem. Not in the Mojave.

You are attempting to grow a rose in very challenging conditions. Good quality soil and a thick mulch to hold in what moisture exists is mandatory. Is the soil around your rose thickly mulched? Five inches of good soil is not enough for a rose--12"-18" would be better. Did you dig up and amend the entire area before you planted the rose?
A mulch of shredded plant material is a necessity and needs to be regularly renewed. This keeps the soil a little cooler and a little moister.

Is the rose getting enough water? A drip system that slowly soaks the area around the rose would be far better than sprinklers or a hose.

Don't worry about the bark. Bark is the plants way of protecting itself. You are in an area of extreme heat and some winter chill and extreme dryness. Bark build up seems inevitable.

As to ants, we have them here as well in a big way. They can clear large air pockets around the rose roots and dry out the rose rapidly without you ever seeing any trouble on the surface. Pet and child safe ant baits do work over time to keep the area clear so that the rose roots have a better chance. You can make an effective ant bait yourself that is extremely cheap with boric acid, water, and a touch of sugar. (google up the details).

On the good side of your climate, you'll never need to worry about foliar disease. It will be a matter of some trial and error to get good performance from roses in your yard, so keep trying--you might look around for locals who have been successful and ask them for additional tips. Good luck! :)

Thanks hoovb, any planting here is challenging. Roses actually do very well here though the best bloom times are Spring and Fall.

I have been doing the amending of the soil, mulching to protect roots and moisture. Abe is on a drip system but I am frustrated w/it. I often check the roses with a moisture probe to make sure I'm not missing anything.

The bark does concern me still as it pulls away in areas and as I said, it's almost hollow except for the powdery red stuff underneath. It makes me wonder if I should protect the trunk with water pipe insulator foam for a few months so it can repair itself.

The ants are terrible and they are desert smart. We finally determined that our home sat on a humungous colony. We were being invaded constantly in every room. I went into my sewing room to iron and ants had completely invaded my iron to get at the water. It's taken two years for the pest service to wipe out the colony under the house but no way could we stop the pest service for even a month.

Ideas on the hollowness under the bark and red powdery stuff? Any organic or chemical treatment necessary?

Red powdery and not orange powdery? Red powdery, I wonder if it is frass from the ants or some other insect eating the inside of the bark. Orange powdery naturally I think of Rust, but i can't imagine you have Rust.

I would make a serious effort to control the ants near that rose and see if the red-powdery resolves itself. The shrinkage of the bark from the stem could be due to extremes of heat and dryness, then insects or ants get in there and go to work. How old is the plant? Did you just put it in recently or has it been there for a number of years?

All of southern California is said to be one enormous Argentine ant colony. :(

It's definitly red. It's not rust. Because we can have such temp swings, I do try to protect trunks in winter from the sun hitting them and warming them up thus causing the bark to swell and split. The rose is probably 9 - 10 yrs old. It was planted in the front yard until 2002 when we had the backyard put in. It has sun daily through the seasons, as it is planted on the south side. I was at Lowe's Sat. and picked up and eco-friendly insect deterrant made from recycled wood product with cedar oil. We'll see how it works before going to nuclear products. As I said these ants are clearly survivors and have learned all sorts of tricks to meet their needs. They don't behave as ants down the hill (down in San Berdo, Ontario, Rancho Cucamonga into LA and Orange Co. Those ants are CA ants, wearing sunglasses and flipflops year round.

Hope you were not in the path of any fires this weekend. Crazy stuff is going on in So CA these years. My son was sent on a strike team to Sylmar on Friday. He is an engineer/firefighter/paramadic. Don't know if he's back yet.

I'll get that product down now and see if I can get the ants running, will also dig it in deep as these guys are below a good portion of time.

Thanks again for your time.

Mary

Mary -- I queried a friend who grows roses in the desert.
I asked him if this rang any bells with him, and I am sorry to say, he said it did not.
So, now, I'm thinking maybe this is something that might warrant having someone from the Dept. of Agriculture look at it.

Jeri

Mary -- Contact me privately?
Your problem intrigues me, and I'm still trying to chase it down.

Jeri Jennings

I just remembered that a former member of my church is an entomologist at UC-Riverside. I'll have to see if I can get an email to him and ask if he can give me any clues.

Hang tight folks, I'll see what I can find out.