Leyland Cypress Interior Yellowing: Shade, Not Disease

7 Leyland cypresses (2 years, NY) show interior yellowing/needle drop. Owner suspected Pestalotiopsis fungus but found tiny bugs on white paper tap test.

Diagnosis: Normal Shade Response

Interior browning on Leylands = self-shading. Outer growth blocks light; inner needles senesce and drop. Universal in maturing evergreens.

Spider Mite Check

Tiny bugs on paper could be spider mites (pinpoint, yellow-red). But mites affect outer foliage too—not just interior. Tap test on green outer foliage to confirm.

Canker Disease Vigilance

Real threat: Seiridium/Botryosphaeria canker. Watch for brown tips on outer branches. Prune 4-6" below discoloration; destroy debris.

Management

• Rake interior debris (sanitation).
• Avoid overhead irrigation.
• Water at base.
• Spacing: 12+ feet for screen plantings (owner planted 10, should have used 5-6).

Long-Term

Trees reach 40-60 ft. Overcrowding guarantees disease. Consider thinning. Fertilize via arborist.