Arborvitae Problems: Why Your Privacy Hedge Is Browning and How to Save It

Arborvitae (Thuja occidentalis and Thuja × Green Giant) is the most-planted privacy hedge in the eastern US. The two dominant cultivars (Emerald Green and Green Giant) handle cold winters, tolerate clay soil, and grow into a solid wall within 5-7 years. They’re also the most-asked-about hedge plants in extension office calls, because they brown out in dramatic patterns when something goes wrong.

Six problems account for almost everything that turns a green arborvitae brown:

• Bagworms (eat the foliage)
• Spider mites (suck the sap)
• Tip blight (fungal, Phomopsis or Kabatina)
• Root rot (Phytophthora, when planted in poor drainage)
• Winter burn (cold dry winds in winter)
• Deer damage (chewing the foliage)

Only two of these are diseases in the technical sense. The other four are pests or environmental problems. But all six look similar from a distance: brown patches, dead branches, declining hedge. This guide covers all six and how to tell them apart.

How to tell which problem you’re looking at

Quick visual triage. Find the most obvious symptom and jump to the section.

• Spindle-shaped brown “bags” hanging from branches, made of silk and foliage: bagworms
• Bronze or rust-colored discoloration across needles, yellow stippling on close inspection: spider mites
• Browning of new shoot tips in spring (Phomopsis) or older twigs in late winter (Kabatina): tip blight
• Whole branches yellowing and wilting, often progressing from the bottom up, especially in wet sites: root rot
• Browning of foliage on the south/southwest/west-facing side after winter, green underneath the brown tips: winter burn
• Clean horizontal cut lines at deer height (typically 4-6 feet), foliage chewed off where you can reach: deer damage

The single most useful diagnostic step on a browning arborvitae is to scrape the bark of a “dead” branch with a fingernail. If green tissue shows underneath, the branch is alive and the foliage will likely recover. If brown all the way through, the branch is dead and won’t regenerate.

Bagworms

Bagworms (Thyridopteryx ephemeraeformis) are the most economically damaging insect pest of arborvitae in the eastern and southern US. By the time you notice them, the caterpillars are often already half-grown and the damage is significant.

What it looks like

The signature is a 1.5-2 inch brown bag, shaped like an upside-down ice cream cone, hanging from the foliage. The bag is constructed from silk and bits of arborvitae foliage the caterpillar has clipped and glued onto its case. Each bag holds one caterpillar (and later, in fall, hundreds of eggs).

When bagworms are actively feeding, you see browning patches of arborvitae foliage where the bags are clustered. The bags themselves blend in surprisingly well with the dark green needles, which is why most homeowners discover them only after the population has been chewing the tree for several weeks.

Why it happens

According to Penn State Extension and other land-grant extension sources, there is one generation per year. Bagworms overwinter as eggs inside the mother’s bag. In late May through June, the eggs hatch and the tiny larvae crawl out, often spinning down on silk threads and ballooning to new host plants. Each caterpillar starts constructing its own bag and feeding on the host foliage.

By August the larvae are about 1.5 inches long. In September they pupate inside their bags. Adult males emerge as small black moths and fly looking for females. Females are wingless and stay in their bags. After mating, each female lays 300-1,000 eggs inside her bag and dies. The eggs overwinter, and the cycle repeats.

What to do about it

The control window is narrow. Catch them in May or June and the population collapses. Wait until August and you’re picking bags off the tree by hand.

• Hand-pick bags if there are only a few. Drop them in soapy water. This works on a single backyard tree with light infestation.
• Spray with Bt (Bacillus thuringiensis) when the caterpillars are small and actively feeding. Bt is a bacterial pesticide selective for caterpillars. It needs to be ingested, so it works only on actively feeding larvae. Apply every 7-14 days through late spring while the caterpillars are tiny.
• Pyrethroid sprays (permethrin, bifenthrin) work on slightly larger caterpillars and have longer residual action. Best applied in late May or early June.
• Neem oil (Bonide Neem Oil concentrate at label rate) is a softer chemical option that works on small caterpillars and also addresses spider mites in a single application.

How to keep it from coming back

• Remove every bag in winter. Before April, walk the hedge with a bucket and pick off every dangling brown bag. Each bag contains hundreds of next year’s eggs. Picking 90% of them reduces next year’s population by 90%.
• Monitor in late May. Check for tiny new bags (1/4 inch) on the foliage. That’s the spray window.
• Encourage beneficial wasps. Several parasitic wasps attack bagworms. Avoid blanket insecticide applications that kill the beneficials.

Spider mites

Spruce spider mites (Oligonychus ununguis) are the second most common arborvitae pest. They suck sap from the needles and produce a characteristic bronze or rust-colored discoloration across affected foliage.

What it looks like

From a distance, the foliage looks dusty and dull, with a brownish or bronze cast instead of the deep green of healthy arborvitae. Up close, individual needles show fine yellow or white stippling where the mites have fed. Severe infestations cause needles to brown completely and drop. Fine webbing may be visible on the underside of branches, especially in dry hot weather.

Spruce spider mites are most active during cool spring and fall weather. They slow down during hot summer months and become dormant in winter. The “summer browning” pattern (looks fine in spring, browns suddenly in May, looks dusty by June) is the classic spider mite signature.

Why it happens

Mites overwinter as eggs on the underside of needles. Warm spring days (50-75°F) trigger hatching, and the mites build to peak populations during May-June. A second peak occurs in September-October. The mites prefer dry, dusty conditions, which is why arborvitae hedges along driveways or roadsides where dust kicks up get hit harder than hedges in moist garden settings.

What to do about it

• Tap test: hold a piece of white paper under a suspected branch and shake the foliage. If tiny dots fall onto the paper and start crawling, you have mites. Big enough to see clearly with a hand lens (1/50 inch).
• Strong water spray dislodges most mites and physically washes them off the foliage. Apply with a garden hose nozzle directed at the affected branches. Repeat every few days during active infestation.
• Horticultural oil or neem oil (Bonide Neem Oil) sprayed during the cool spring or fall period suppresses populations. Spray during active mite season (50-75°F), not during summer heat which can damage the foliage.
• Insecticidal soap also works on mites during active feeding windows.
• Do NOT use broad-spectrum insecticides unless you have to. They kill the predatory mites and beneficial insects that naturally control spruce spider mite populations, often making the problem worse.

How to keep it from coming back

The single best long-term control is keeping the tree vigorous and not stressed by drought. Mite outbreaks correlate strongly with drought stress in late summer of the prior year. Deep watering in fall before winter dormancy reduces mite pressure the following spring.

Tip blight (Phomopsis and Kabatina)

Two fungal tip blight diseases hit arborvitae, though they’re more common on junipers in the same family. The two pathogens cause similar damage but at different times of year, which helps with diagnosis.

What it looks like

Phomopsis blight kills the new shoot tips in spring. First symptoms: yellow spots on young needles. Then the new growth turns dull red, then ash gray, then brown and dead. The fungus enters young succulent tissue and works back toward the older wood. Most damage shows up in May-June.

Kabatina blight kills 1-year-old twigs (the previous year’s growth) during warm weather. Symptoms appear in February or March: yellow or brown discoloration of the branch tips of last year’s growth. Kabatina typically requires a wound to enter the tissue, often a winter injury or insect damage.

Both blights produce small black fruiting structures (pycnidia) on dead twigs that release spores during wet weather. The damage from one branch tip rarely kills the tree but can disfigure the hedge.

Why it happens

Both fungi favor wet humid conditions. Crowded hedges with poor air circulation get hit hardest. Plants stressed by drought, insect damage, or winter injury are more susceptible than vigorous plants. Plants under cool wet spring conditions are most at risk for Phomopsis. Kabatina prefers warmer weather and exploits the winter-injured tissue many arborvitae have on the south side after a cold winter.

What to do about it

There are no chemical fungicides that reliably control tip blight on arborvitae. Management relies on:

• Pruning out dead and dying tips in dry weather. Cut several inches below visible dieback into clean live wood. Sterilize blades between cuts with 70% alcohol.
• Improving air circulation by selective thinning if the hedge is overgrown.
• Watering at the root zone, not overhead. Wet foliage at night drives fungal spread.
• Maintaining tree vigor with appropriate fertilization and irrigation. Drought-stressed trees attract both Phomopsis and Kabatina.

For severe recurring cases, a copper fungicide application during the wet spring period can suppress some new infections, though Phomopsis is harder to control chemically than most foliar fungi. Bonide Copper Fungicide at label rate, applied at bud break and again 14 days later, is the home-garden option.

How to keep it from coming back

• Plant the hedge with adequate spacing (4-5 feet between trees for Emerald Green, 8-10 feet for Green Giant)
• Avoid wet, shaded sites
• Don’t use overhead sprinkler irrigation
• Address winter burn promptly so injured tissue doesn’t become a Kabatina entry point

Root rot

Phytophthora root rot is the most common reason a long-established arborvitae hedge slowly declines without an obvious pest or pathogen problem. The disease is soil-borne, attacking the roots before any above-ground symptoms appear.

What it looks like

• Branches yellowing and dying, often progressing from the bottom of the tree upward
• One or more trees in a row declining while neighbors look fine
• Stunted growth and sparse foliage even in spring
• Soft, dark, decayed roots when you dig down
• Often associated with low spots in the landscape, poorly drained soil, or recent grading changes
• Sometimes a faint orange or brownish stain visible at the soil line of affected trees

The disease progresses slowly, often taking 2-4 years to kill a mature tree. The pattern of slow decline of individual hedge trees while neighbors thrive is the classic signature.

Why it happens

Phytophthora species are water molds (technically not true fungi) that thrive in saturated soil. They produce mobile zoospores that swim through water films in the soil and infect arborvitae roots through natural openings or small wounds.

Risk factors:

• Heavy clay soil with poor drainage
• Areas where rainwater accumulates after storms
• Sprinkler systems creating chronically moist soil
• Soil compaction from construction or heavy foot traffic
• Recent regrading that buried the root flare or changed water flow

What to do about it

By the time above-ground symptoms appear, the disease has progressed too far for most home-garden interventions to reverse it. Catching it early on one or two trees allows for some management:

• Improve drainage immediately. Install French drains, add organic matter to break up clay, or regrade to direct water away from the hedge.
• Cut back on irrigation. Reduce watering frequency. Switch from overhead sprinklers to drip if possible.
• Apply a fungicide drench with fosetyl-al or mefenoxam to suppress active infection. This is supportive, not curative.
• Replace severely declined trees with new arborvitae on improved soil, or switch to a more drainage-tolerant species (Norway spruce, hemlock in shaded sites, leyland cypress in zones 6-9). Our columnar evergreen trees guide covers alternative species.

How to keep it from coming back

The single best prevention is site selection. Arborvitae need well-drained soil. In heavy clay or low spots:

• Plant on raised mounds 6-8 inches above grade
• Mix in 30% coarse compost or pine bark fines with the native soil at planting
• Install a French drain or perimeter drain on sites with chronic moisture
• Don’t bury the root flare. The transition from trunk to roots should be visible at the soil line.

Winter burn

Winter burn is the most common cause of browning on Emerald Green arborvitae specifically, especially on the south, southwest, and west-facing sides of trees exposed to winter sun and wind.

What it looks like

Brown or rust-colored foliage on one side of the tree, typically the south or southwest side, appearing in late winter or early spring (February-April). The browning is usually most severe on the outer foliage, with the inner foliage staying green. The damage looks dramatic and homeowners often panic and call arborists, but most winter burn isn’t fatal.

Why it happens

Winter burn isn’t a disease. It’s desiccation injury. The mechanism:

1. Winter sun and wind cause foliage to lose water through transpiration
2. The ground is frozen, so roots can’t replace the water
3. Foliage cells dehydrate and die
4. The tissue browns when the temperature warms in spring

Trees that go into winter with dry soil (the most common scenario) are at the highest risk. Trees with sun-exposed south or west sides, no windbreak, no winter mulch, and no late-fall deep watering are the typical victims.

What to do about it

For trees already showing winter burn in spring:

• Wait to prune until late spring or early summer. Brown tips may regenerate. Scratch the bark of a “dead” branch with a fingernail. If green tissue shows underneath, the branch will recover and push new growth from buds further back. If brown all the way through, cut back to the nearest live wood.
• Water deeply as soon as the ground thaws. Help the tree rehydrate.
• Don’t fertilize stressed trees until they’ve recovered. New growth requires healthy roots, which winter-burned trees may not have yet.

How to keep it from coming back

Five preventive habits handle winter burn:

• Deep fall watering in October and November before the ground freezes. Saturate the root zone weekly until the first hard freeze. Single highest-leverage intervention.
• Mulch the root zone with 2-3 inches of wood chips. Moderates soil temperature and reduces frost depth.
• Apply anti-desiccant spray (Wilt-Pruf, Wilt-Stop) in late November. Coats the foliage with a thin waxy film that reduces water loss through transpiration. Reapply in late January if winter is severe.
• Burlap wrap for newly planted trees in their first 1-2 winters. Wrap the south and west sides of the tree (not the whole tree) to shade the foliage from harsh winter sun. Remove in March.
• Pick the right cultivar for your climate. Emerald Green is more prone to winter burn than Green Giant in cold-winter zones. Our emerald green arborvitae guide and green giant arborvitae guide cover the cultivar-specific cold tolerance and care requirements.

Deer damage

Deer love arborvitae. Of all the privacy hedge options, arborvitae is one of the most heavily browsed by deer in winter when other food is scarce. A hedge planted near a wooded edge in a deer-pressure region can be eaten down to bare stems in a single bad winter.

What it looks like

• Clean horizontal cut lines at deer height, usually 4-6 feet above the ground
• Foliage stripped off the front-facing side (the side toward the deer’s approach path)
• Stubs of stripped twigs where deer have ripped foliage off rather than cleanly cut it
• The lower portion of the hedge (below 4 feet) might be intact while the upper portion is stripped if deer have been pressing into the hedge

Why it happens

Deer eat what’s available in winter. In landscapes with woods nearby, a planted arborvitae hedge is a 4,000-calorie salad on cold days when natural browse is unavailable. The damage is most severe in:

• Late winter (January-February) when deer pressure peaks
• Deep-snow winters when ground forage is buried
• Rural and suburban edges where deer populations exceed natural carrying capacity
• Areas with no human activity to discourage deer

What to do about it

For trees already browsed:

• Wait until spring to see how much recovery happens. Many heavily browsed arborvitae regrow from below the browse line within 1-2 growing seasons.
• Prune damaged branches back to clean live wood in late spring.
• Set up deer protection for the next winter.

For preventive deer management:

• Deer repellents sprayed monthly through fall and winter work for most home properties. Bobbex Deer Repellent Concentrate is the home-garden standard and is specifically listed as effective on arborvitae in regional extension recommendations. A quart of concentrate runs $20-25 and treats a 50-foot hedge for a season. Reapply every 4-6 weeks and after heavy rain.
• Fencing: an 8-foot fence works. A 6-foot fence works if deer pressure is moderate. Anything shorter than 6 feet is decorative.
• Plastic deer netting over the hedge for the winter (October through April) creates a physical barrier that’s invisible from a distance and cheap. About $50-100 to cover a 50-foot hedge for one winter.
• Companion plants that deer dislike planted around the arborvitae base provide partial deterrence. Lavender, boxwood, daffodils, alliums, and many herbs are deer-resistant.

For more detail on landscape-wide deer management, our protecting trees from deer guide covers fencing options, repellents, and resistant plant choices.

How to keep it from coming back

In a high-deer area, you can’t eliminate the damage without fencing or aggressive repellent rotation. Repellents work best when used preventively (before damage starts) and rotated to prevent deer from getting used to one scent or taste. Combination treatment (repellent + companion plants + netting in deepest winter) is more effective than any single approach.

In severe deer-pressure regions, consider an alternative privacy hedge species that deer don’t browse:

• Boxwood (deer-resistant)
• Cypress varieties (less preferred by deer)
• Holly (thorny foliage)
• Japanese yew (mildly toxic to deer)

Our privacy shrubs and hedges guide covers alternatives by region and deer-resistance rating.

When to call an arborist

Three situations warrant a professional visit. First, a hedge declining without an obvious cause where root rot, herbicide drift, or soil contamination needs investigation. Second, a multi-tree decline where you need to decide between aggressive intervention and full hedge replacement (significant financial decision). Third, deciding which cultivar to replant when the existing hedge has chronic problems matching a different species or rootstock recommendation.

An ISA-certified arborist consultation runs $75-200 in most US markets. Find one through the Trees Are Good arborist locator or read our guide to what an arborist does before you call. If individual trees in the hedge need to come out, tree removal on a 15-25 foot arborvitae typically runs $200-600 per tree.

Prevention checklist

Seven habits cover almost all arborvitae problems:

• Pick the right cultivar for your conditions. Green Giant for fast growth and cold tolerance (zones 5-8). Emerald Green for narrow columnar form (zones 3-7). North Pole or Sting cultivars for the narrowest spaces. Our tall narrow shrubs guide covers space-constrained options.
• Plant on well-drained soil. Mound the planting area 6-8 inches if drainage is questionable. Mix coarse compost into clay.
• Space adequately. 3-4 feet between Emerald Greens for a hedge, 8-10 feet for Green Giants.
• Deep fall watering in October and November. Single best winter burn prevention.
• Apply Bobbex or another deer repellent monthly from October through March in deer-pressure areas.
• Walk the hedge in winter and pick off bagworm bags. Single best bagworm prevention.
• Watch for spider mites in cool spring weather. Tap test in May. Spray with horticultural oil or neem at first signs.

For broader landscape disease patterns, see our tree fungus guide. For evergreen alternatives if arborvitae isn’t working at your site, our columnar evergreen trees guide covers Italian cypress, Leyland cypress, and other narrow upright options.

Frequently asked questions

Why is my arborvitae turning brown?

Six possible causes, each with a different fix:

• Brown on the south side after winter: winter burn (fix: deep fall water, anti-desiccant)
• Bronze/dusty browning in spring: spider mites (fix: water spray, horticultural oil)
• Brown bags hanging from foliage: bagworms (fix: hand-pick, Bt spray)
• Brown shoot tips in spring: tip blight (fix: prune affected tips, copper spray)
• Whole branches yellowing from the bottom up: root rot (fix: improve drainage)
• Clean horizontal cut lines at deer height: deer browse (fix: repellent, fencing)

Can I save an arborvitae with winter burn?

Usually yes, especially if the inner foliage is still green. Don’t prune brown branches until late spring. Scratch the bark with a fingernail. Green tissue underneath means the branch is alive and will push new growth. Brown tissue all the way through means cut back to live wood. Most lightly winter-burned arborvitae fully recover within one growing season.

What’s eating my arborvitae?

Two main candidates: bagworms (look for 1.5-2 inch brown bags hanging from foliage, summer damage) or deer (look for horizontal cut lines at 4-6 feet, winter damage). Spider mites also “eat” arborvitae in a manner of speaking by sucking sap, but they don’t produce visible chewing damage. Look at the foliage with a hand lens for tiny moving dots if you suspect mites.

Will deer eat my arborvitae?

Yes, deer love arborvitae, especially in winter when other browse is unavailable. The two most common deer-pressure cultivars (Emerald Green and Green Giant) are both attractive to deer. Spraying Bobbex Deer Repellent monthly from October through March is the standard home-garden defense. For severe deer-pressure properties, 8-foot fencing or alternative deer-resistant species are more durable solutions.

How do I get rid of bagworms on arborvitae?

Hand-pick all visible bags in winter before April (when eggs hatch). For active infestations in late spring and early summer, spray Bt or a pyrethroid every 7-14 days while the caterpillars are small. By August the bags are too large and the chemicals don’t penetrate well, so hand-picking becomes the main option.

What’s the difference between Emerald Green and Green Giant arborvitae?

Emerald Green (Thuja occidentalis ‘Smaragd’) is a narrow columnar form, 12-15 feet tall and 3-4 feet wide. Slow-growing (8-12 inches per year). Hardy to zone 3. Best for tight spaces. More prone to winter burn and deer damage. Green Giant (Thuja × ‘Green Giant’) is a fast-growing pyramidal form, 50-60 feet tall and 12-18 feet wide. Grows 3-5 feet per year. Hardy to zone 5. Best for wide privacy hedges. More tolerant of deer (though still browsed in heavy pressure). Our Emerald Green guide and Green Giant guide cover the cultivar-specific care.

Should I prune brown arborvitae branches in winter?

No, wait until late spring or early summer. Many brown branches that look dead in winter recover with new growth from buds further back on the branch. Pruning too early removes tissue that would have regenerated. The exception is obviously dead-and-broken branches from snow load, which can be removed any time.

Are arborvitae problems contagious between trees?

Most are. Bagworms ballooning from one tree to another on silk threads is the normal spread pattern within a hedge. Spider mites walk between adjacent plants. Phomopsis and Kabatina tip blight spores spread by splashing rain. Phytophthora root rot spreads through shared soil and water flow. Winter burn is environmental, not contagious, but a hedge experiencing winter burn shows the damage on all trees with similar sun and wind exposure. Treating the hedge as a single management unit makes most interventions more efficient.