What's killing my trees

Asked June 8, 2020, 3:43 PM EDT

Hi! Can you tell what's killing my trees? One things the pics don't show is that they have some webs ... not sure if that's just from spiders or it's part of the problem. I do not see any bag worms. Thanks!

Howard County Maryland

1 Response

We cannot see the webbing in the photos, though these Dwarf Alberta Spruce (Picea glauca 'Conica') do tend to contract spruce spider mites in cool weather (the damage becomes more visible in warm weather, however). Spiders are also possible, in which case the webbing would be harmless. The native range of these spruce is to areas much cooler (especially with overnight summer temperatures) than our climate here in the mid-Atlantic. The only spruce that naturally grow this far south are remnant colonies in our weastern-MD high-elevation habitat.

The chronic stress the trees experience can make them more vulnerable to pest and disease issues. They are also sensitive to the more compacted soils in suburbia and can suffer root loss as a result. There are no practical treatments for any ailment save for the mites, which can be treated with horticultural oil if necessary: https://extension.umd.edu/hgic/topics/spider-mites-trees-and-shrubs#appears.

The branches with lost needles will not re-foliate and should be pruned off. This may understandably ruin the shrub's desired dense, conical shape, and as such you might consider outright replacement. Other evergreen shrubs grown in this shape can be better substitutes, though each comes with its own set of potential pests or diseases in times of stress. There will be a greater range of options if shrubs that do not stay pyramidal/conical like this variety are considered.