Unfortunately, without further information, I can not tell you exactly what may be wrong with your plant. Depending on the species and the climate of your area, you may be having issues with heat, water, microclimate, disease or possible insects. If the plant is new to the location it may be losing branches from transplant stress or transport damage. If the branches are brittle I would suggest pruning those branches out and disinfecting your pruners between each cut. Disinfecting is a good practice if there is a possible disease.
It appears from the photo that you are located in Southern Nevada and I am not aware of the recent climate and insect issues as I am located in the north where we have snow and freezing temperatures.
You can also contact your local Cooperative Extension office. You can find your local Extension office at unce.unr.edu