If you are sure there is no insect problems and the trees are getting enough sun & water.
Then, maybe the ph level of the soil is not correct for roses in those areas having trouble? Have you ever had a soil test done?

Read this link on PH levels.
http://www.rosemagazine.com/articles04/ph/

Are you absolutely certain that the 3 poor performers are getting as much water as the other 3? Is drainage the same? If drainage is good, it's hard to over-water newly planted roses -- and that, I've found, is especially true of tree roses.

OTOH, if there is poor drainage on the side where the roses are struggling, soggy conditions could produce what you've described.

I don't think I would fertilize right now. Because your roses are new, there is probably some residual, still active timed-release fertilizer around the roots. If you do fertilize, mix the solution at half strength until you begin to see an improvement, or use an organic like liquid seaweed or fish emulsion.

What type of soil do you have? When it rains do you have standing water that doesn't soak in right away or does the water drain down through the soil well?
jaxondel and windeaux are right that it can cause those problems also.
Whatever it is, it probably has something to do with the soil in those areas.
Best of luck!

Well Thank-you so much for the words of advice!

Jim, the soil was tested before we planted the vineyard back in Feb. 2005. We amended to all the specifications, and the vineyard is THRIVING. still. The soil here is mostly clay, and we've had a VERY WET spring. The entire area is covered with pathway mulch (wood shavings/chunks), and does drain pretty well in the areas in question. (no standing water, unless its pouring).
But the 3 happy (west side) trees probably get more aft. direct sun. As I've noticed the 3 poor performers, I've watered occasionally. Maybe I'm making it worse by doing that, eh?

So, hold off on the fertilizer Jaxondel, even though they were 2 yr. olds when planted in Feb?

thanks again.

How much total direct sun per day are the sickly ones getting?

The sickly guys are getting 7-8 hrs. sun daily, but some of that later sun is filtered by the vines and endposts. I just went out and, after removing the mulch from trunk area, I stuck my finger in the soil. Its quite wet. The 3 happy ones, did same, and just moist.

so, shall I remove all mulch from their base, and leave them be?

Push the mulch back a bit and let the area dry out some.
Some people recommend using raised beds when having trouble with heavy clay soils that will not drain correctly.
Some people ammend the entire planting area 12" or so down.
But, first you need to find out exactly what it is before making any drastic changes.
Hopefully your getting enough direct sun. Most roses need 6+ hours of direct sun to thrive. Filtered is filtered, not direct.
That's why everybody should have there PH checked and provide good drainage BEFORE planting roses. Also making sure the sun requirements are correct for there type of roses.

we knew we had/have alkaline soil and with a high water table when we planted the vines. I am told roses like that kind of soil and act as a precursor to disease, if present. Roses show signs of 'something', and then you treat the grape vines too.
so i'll push off the mulch, and hope for no more wet stuff!
thanks for taking the time to help.

I myself planted our first rose in a area that had very bad drainage (clay soil). But, it has never showed signs of being unhappy yet. It was planted in 2007. It gets about 9 -10 hours of direct sun though.
I've been top-dressing a large area of the soil underneath the rose with well composted (manure) and placing used coffee grounds down to attract earthworms. Earthworm activity helps loosen up the soil.
Organic fertilizers like Mills Magic Rose Mix, etc. will help soil also.
But, in your case, your having trouble with your tree roses.

teresa44,

I forgot to mention. Our PH level is 6.5 up where I have our first rose planted in heavy clay/ poor drainage soil.
I have a Japanese Snowball (Viburnum) planted in that poor area also. Both are doing fine so far though.
In spring after everything leafs out, I place used coffee grounds in these areas, sometimes organic fertilizer, then cover that with 1/2" or so of well composted manure, then alittle hardwood mulch on top of that.
Well, I hope you get your problem figured out! Best Wishes!