Die Back is the blackening of the tip of the rose stem which then travels down toward the graft.
There are two main reasons for this to happen with a newly planted rose bush.
The first is the most common - Not enough water.
Roses need a lot of water when newly planted as their roots have not established themselves.
The second cause is acidic soil or fertilizer used at the time of planting.
Roses need a ph of about 6.5 which is only slightly on the acidic side of neutral. If too low, any new root development will literally burn off.
If you know you have placed fertilizer in the soil at the time of planting you may have to replant the rose. Otherwise you may wish to do a pH test on the soil and get advise from a good garden shop in your area. Click here fore more information on soil pH.
Please note that die back can also be a perfectly normal occurrence. Roses use large amounts of energy to continually reproduce stems and flowers, therefore they become very economical with their growth. If the rose no longer requires a stem or part of the stem it will stop the sap flow, killing off that area. This will occur on the very tips of stem where no growth is evident. However this is not to be confused with other causes of die back as they can cause significant damage to your rose.
If die back has occured, cut off the affected area. When making the cut ensure that the stem is white the entire way through, without any 'bruising'. If die back is not removed it will continue to travel down the stem and will eventually kill the plant. Attempt to fix the cause of the die back, helping to prevent it from re-occuring.
Important: signs and symptoms will vary significantly between varieties, even within similar categories. The information provided here is a basic summery of the most common affects and will not always be applicable to all rose varieties.