Symptoms of Dieback on Arborvitae Trees. (Photo: MU-PDC client)

Landscape coniferous plants such as Arborvitae (Thuja spp.), Spartan Juniper (Juniperus chinensis 'Spartan'), Eastern Red Cedar (Juniperus virginiana), Eastern White Pine (Pinus strobus) and Spruce (Picea spp.) are widely planted for privacy screens and windbreaks in Missouri landscapes. However, over the past few months, the MU Plant Diagnostic Clinic and extension specialists statewide have seen a dramatic influx of samples and inquiries regarding branch browning, tip dieback, and full-canopy decline of these plants, especially Green Giant Arborvitae (Thuja x 'Green Giant') and Emerald Green Arborvitae (Thuja occidentalis 'Emerald').

While it is tempting to blame a single aggressive fungal disease, what we are witnessing in Missouri landscapes is a classic disease pyramid where severe environmental and cultural stress directly paves the way for opportunistic pathogens, causing disease pressures on certain susceptible trees.

Symptoms of Dieback on Cedar Trees in Columbia, Missouri (Photo: MU-PDC)

The Main Drive: Environmental Stress

To understand why an evergreen tree is declining today, we must look back at the timeline of weather events over the past twelve months. A few coniferous plants, such as Arborvitae, possess shallow, fibrous root systems that make them highly sensitive to moisture fluctuations.

Missouri has experienced one of driest winters from last year and drought stress is likely the major issue causing so many shallow-rooted evergreens dieback. These trees experienced winter dehydration by wind and frozen injuries as well as sun scalds due to drastic fluctuation of temperature earlier in 2026. All these factors led to potential foliage dieback and root mortality. Because of the thick, waxy cuticle on arborvitae foliage, the top of the tree may remain deceptively green for months while the roots are actively dying.

The Opportunists: Fungal Tip/Needle Blights

When conifers suffer root loss from drought and leaf tissue injury from winter desiccation, their natural defenses deplete. This creates a prime entry point for weak or secondary fungal pathogens that would otherwise struggle to infect a vigorous, healthy tree.

In addition to disease problems of spruce that were detailed in “Spruce Trees are Neat, but be Aware of Their Diseases in the Spring”, common tip and needle blight diseases diagnosed on stressed Missouri evergreen trees are:

This fungus specifically targets Thuja species. The infection typically starts at the very tips of the needles and migrates backward toward the inner branch. Under humid spring conditions, at the transition zone between dead and living tissue, the fungus produces black, pimple-like fruiting structures called pycnidia that rupture through the needle epidermis.

Pestalotiopsis Tip Blight (Pestalotiopsis funerea)

This fungus is an extremely common secondary invader across the Midwest but is rarely a primary pathogen. It heavily relies on winter-injured, physically damaged, or drought-stressed tissue to gain access and causes a progressive yellowing-to-browning of twigs, producing distinct black pycnidia under wet conditions like Phyllosticta.

Diplodia Tip Blight (Diplodia sapinea)

This fungal disease targets stressed ornamental pines, such as Austrian, Scots, and Mugo pines. It attacks the newly developing needles right as they expand in the spring. The damage usually starts on the lower branches and moves upward. Tiny black pycnidia are produced at the base of the dead needles or the scales of mature pinecones.

Unlike Diplodia spp. that attacks new growth in its tracks, Mycosphaerella spp. target older needles of pines first, causing reddish spots and bands on the needles. As it progresses, the whole needle turns brown, dies and falls off the tree. Once the spores are mature, they emerge from pycnidia in the spots or bands on the needles and can be spread by rain or wind.

Phomopsis and Kabatina Tip Blight (Phomopsis juniperovora and Kabatina juniperi)

These are two common tip blight diseases of cedar trees, causing needles to turn reddish, brown to grey in color. Both can produce pycnidia. During rainy spring weather or via overhead irrigation, these fruiting bodies release massive amounts of spores that are splashed to healthy neighboring branches, rapidly amplifying the dieback.

The Solutions: Integrated Management Strategies

Because this problem is an overlap of cultural, environmental, and biological factors, relying solely on a fungicide spray will not solve the underlying issues. An integrated approach is required:

• Sanitation: Prune out and destroy infected branches during dry weather to reduce the inoculum population. Rake up and discard fallen, blighted needles from beneath the canopy. Do not compost this material, as these fungi can overwinter in home compost piles. Always sanitize your pruners with 10% bleach or 70% alcohol between cuts to prevent spreading spores. Avoid pruning trees during spring and early summer as the fungus can also infect wounds.
• Avoid Over-fertilization: Excess nitrogen imposes more stress to the trees and potentially increases disease severity of tip and needle blight disease of evergreen trees.
• Adjustment of Irrigation Practices: Avoid overhead watering, which wets the foliage and assists spore dissemination. Transition to drip irrigation or soaker hoses to deliver water directly to the soil.
• Provide Supplemental Summer Water: Ensure the plants receive deep watering (1 inch per week) during extended dry summer periods. Avoid planting evergreen trees in heavy, poorly drained area because poor drainage will cause root rots, leading to drooping and flagging symptoms that resemble drought symptoms above ground.
• Chemical Options: For high-value landscape specimens or trees with a history of severe blight, preventative fungicide applications can be made in the spring as new growth emerges. Look for ornamental-labeled products containing chlorothalonil, mancozeb, or copper hydroxide.
• Consider re-planting: Avoid planting highly susceptible trees or nonnative species. Increase spacing to improve air circulation. Proper mulching allows trees to establish and thrive by suppressing the growth of weeds, conserving the soil moisture and regulating soil temperature.

Need a Disease Diagnosis?

If your evergreens are showing progressive dieback and you want to confirm whether a fungal pathogen or an insect pest like spider mites or scales are present, submit a physical sample showing the transition from live to dead tissue to the MU Plant Diagnostic Clinic.

For submission forms and digital diagnostic assistance, visit the portal at: extension.missouri.edu/services/plant-disease-sample.