Tree Pests & Diseases

From drought-stressed trees to invasive insects, Colorado landscapes face a distinct set of pests and diseases that can quietly compromise tree health.

CONIFER TREES

A conifer is a tree that produces cones instead of flowers and typically has needle- or scale-like foliage rather than broad leaves. Common Colorado conifers include pine, spruce, fir, juniper, and cedar. Most conifers are evergreen, meaning they keep their needles year-round.

Why Technique Matters:

Proper watering timing, mulching depth, pruning practices, and species selection are critical in Colorado. Techniques that work elsewhere—especially aggressive pruning or summer fertilization—can actually weaken conifers here rather than help them. Caring for conifers in Colorado isn’t the same as in milder or more humid regions. A few factors make our conditions unique:

Dry air & low humidity
Conifers lose moisture through their needles all winter long, making them especially prone to winter desiccation.

Alkaline, compacted soils
Many Colorado soils limit nutrient uptake, leading to issues like chlorosis, poor root development, and slow growth if not managed correctly.

High elevation & intense sun
Strong UV exposure stresses needles and bark, increasing the risk of needle scorch and sun damage, even in winter.

Temperature swings
Rapid freeze-thaw cycles can damage roots and trunks, particularly in newly planted or shallow-rooted conifers.

Regional pests & diseases
Colorado conifers are commonly impacted by spruce beetle, pine engraver beetle, needle cast diseases, and cytospora canker, all of which require early detection and targeted treatment.

Conifer Tree Pests & Diseases

DECIDUOUS TREES

A deciduous tree is a tree that drops its leaves each fall and enters dormancy during winter. Common deciduous trees in Colorado include maple, oak, ash, elm, cottonwood, honeylocust, and aspen.

Why Technique Matters:

In Colorado, when and how deciduous trees are pruned, watered, and treated matters as much as what is done. Techniques used in other regions can leave trees vulnerable to stress, pests, or long-term structural problems here. Deciduous trees in Colorado face a distinct set of environmental stresses that affect growth, structure, and long-term health:

Short growing season
Late spring frosts and early fall freezes limit recovery time, making proper timing of pruning, fertilization, and treatments critical.

Alkaline, low-organic soils
Many deciduous species struggle with nutrient uptake, leading to iron chlorosis, poor leaf development, and canopy thinning without soil-specific management.

Heat, drought, and sudden weather swings
Hot summers followed by rapid temperature changes place stress on leaves and vascular systems, increasing the risk of leaf scorch, branch dieback, and decline.

Structural challenges
Fast growth combined with snow load and wind increases the likelihood of weak branch attachments and storm damage if trees aren’t pruned correctly when young.

Regional pests & diseases
Common Colorado issues include emerald ash borer, aphids, scale insects, bacterial leaf scorch, fire blight, and various canker diseases, all of which benefit from early identification and proactive care.

Deciduous Tree Pests & Diseases

ORNAMENTAL TREES

An ornamental tree is selected primarily for its aesthetic features—such as flowers, foliage color, bark texture, or overall form—rather than shade or size. Common ornamental trees in Colorado include crabapple, flowering pear, serviceberry, hawthorn, Japanese tree lilac, redbud, and ornamental plum.

Why Technique Matters:

With ornamental trees, precision matters. Correct pruning timing, careful watering, and proactive disease management are essential in Colorado—missteps can affect both the health and appearance of the tree for years. Ornamental trees are often more sensitive to environmental stress, which makes Colorado’s growing conditions especially challenging:

High stress from climate extremes
Late frosts, intense sun, and temperature swings can damage buds, blooms, and young growth, reducing flowering and overall appearance.

Soil limitations
Many ornamentals prefer slightly acidic, well-drained soils, while Colorado soils are often alkaline and compacted, increasing the risk of nutrient deficiencies and root stress.

Water sensitivity
Ornamentals typically have shallower root systems, making them more vulnerable to drought stress, overwatering, and inconsistent irrigation.

Structural and form issues
Poor or improper pruning can quickly ruin the natural shape of ornamental trees, leading to weak branching, reduced flowering, and long-term health problems.

Disease pressure
Common Colorado issues include fire blight, powdery mildew, leaf spot diseases, and cytospora canker, which can spread rapidly in stressed or improperly maintained ornamentals.

Ornamental Tree Pests & Diseases