Answer: Red tipped photinia is recommended by the University of Idaho for growing in the Boise region. Photinia is subject to fungal spots but it is generally due to wet weather (or humidity if you're near the coast). I don't think the plants will develop the disease if you avoid overhead watering and allow enough space between the plants to encourage good air circulation. You should be able to plant them 6-8' apart and get good coverage for a dense privacy screen. The beauty in these plants is the new growth, which begins red and turns green with maturity. You'll want to shear the plants annually to encourage lots of healthy new growth. Shearing will remove any spotted leaves, as well. Since they can grow to 25' high and wide, keeping them at 3' wide will be a bit of a challenge. Have you considered growing a narrow upright evergreen shrub instead? Thuja or Skyrocket juniper might be better choices.
Best wishes with your landscape!
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