· Gardenality.com's Answer
· If no insects are present at this time, and as long as the Barberry make it through this year you may want to do a systemic insecticide next Spring 2012. There's a season long systemic insecticide called Imidacloprid. Most garden centers carry it. Bayer, Fertilome, and many other chemical companies make the product. You can purchase it in liquid or granular form. The liquid is better and has a season long residual. The granular only works for 3 months... if I'm not mistaken.
Are the branches dying, or is it only the foliage looking bad? If it's only the foliage then the plants should survive and it's probably an insect probelm. If branches are dying it may be a fungus or disease. If so, prune off all of the dead branches. Remove all leaves from the ground around the plant. Spray a systemic fungicide. Fertilome carries a good product called Liquid Systemic Fungicide. There are others as well. Every garden center should have systemic fungicide.
Let me know if what I've suggested doesn't sound like the right solution.