Blue Spruce NeedleCast
Please see our website on needle cast diseases. You did not mention how old the trees are and who diagnosed the disease. Please give us more information.
In general, Older trees rarely warrant spraying. Pruning out severely infected branches is the best control method on branches that show sparse growth.
The spruce trees are probably 18 years old. They are fairly close together which I suspect is part of the problem
It would be helpful if you could submit photos of the whole tree, around the base of the tree, and affected foliage so we can see what you may be dealing with.
That is about the age range where problems show up on these trees, which are native to areas further north.
Pruning out dead areas and making sure that the trees are watered in times of drought can help them look better and hang on.
Take a look here for one of the more common possibilities, which is a fungal disease: http://extension.umd.edu/sites/extension.umd.edu/files/_images/programs/hgic/Publications/HG400_Cyto...
You could consider having a tree health expert, a certified arborist, do an on-site evaluation of the tree's health, and offer an assessment. You can search for a certified arborist at www.treesaregood.org