Lawson Cyprus disease

[Dryad's saddle]

 

27 young lawsons all recently planted all died and have turned a blackish green colour with what looks like a fungal mouldy layering all over the scales. Any ideas?

[KTSmith]

Could it be a sooty mold associated with Cypress aphid? There likely wouldn't be any aphids on the dead parts now, but you might see some at the margins of the killed/living tissues. Or the aphids from early summer may have entirely moved along, leaving the foliage and branchlets with impaired translocation capacity. Then, late summer heat and dry conditions can make evident the earlier infestation, even without the aphids. In that scenario, the sooty mold is more an indicator of the insect than a primary pathogen.