Arborvitae Hedge Dieback: Cercospora Blight Fungicide Program

30 arborvitae (10 yrs) thriving until last summer: 3 consecutive browned bottom-up, then 2 more, now 1 more starting. Rest healthy. Cause? Save last one?

Diagnosis: Cercospora Blight

Fungal disease starting low/inside, moving up/out. Bronze to brown to gray foliage. Fuzzy spores on dead needles. Favored by warm, wet weather. Rocky Mountain juniper highly susceptible; Oriental arborvitae also affected.

Fungicide Protocol

• Apply mancozeb or Bordeaux mixture in early June, repeat early July.
• Third application mid-late July if wet summer.
• Cover lower 2/3 of crown thoroughly.
• Monitor yearly; may not need annual sprays once controlled.

Decision on Affected Tree

If only starting, treatment may save it. If far advanced, remove to reduce spore source.