Leyland Cypress Diseases and Insect Pests in South Carolina

Quick Guide: Leyland Cypress Diseases and Insect Pests

Affected Plants:

• Leyland cypress (× Cupressocyparis leylandii)

Primary Disease Types:

• Canker diseases
• Root rot
• Needle blight

Primary Insect Pests:

• Bagworms
• Spruce spider mites
• Scales

Primary Causes:

• Plant stress
• Drought
• Poor drainage
• Overhead irrigation
• Wounding

Most Important Prevention Strategy:

• Maintain vigorous growth through proper spacing, irrigation, and well-drained soil

Chemical Control:

• Limited effectiveness for large trees; targeted fungicides and insecticides may help when applied early

Leyland cypress (x Cupressocyparis leylandii) is a popular fast-growing screening plant in the Southeast. Due to increased planting driven by its popularity, various diseases and insect pests are more common.

How to Prevent Leyland Cypress Diseases and Insect Pests in South Carolina

As with any plant, the first step to a healthy Leyland cypress is providing it with the proper cultural conditions necessary for healthy, vigorous growth. Healthy plants are better able to survive disease and insect problems than stressed ones.

Generally, Leyland cypress requires full sun and prefers moist, well-drained, moderately fertile soil.

For further details on providing a Leyland cypress with the conditions under which it grows best, see HGIC 1013, Leyland Cypress

These diseases and insect pests are especially common on Leyland cypress in South Carolina landscapes.

Leyland Cypress Diseases: Seiridium Canker (Seiridium unicorne) on Leyland Cypress

Seiridium canker is one of the most destructive fungal diseases affecting Leyland cypress in South Carolina landscapes.

Cause

Seiridium canker is caused by the fungus Seiridium unicorne.

The fungus survives winter in infected tissue.

Produces spores in small, black fruiting structures visible with magnification on the surface of the canker.

Spores spread by:

• Rain
• Overhead irrigation
• Contaminated pruning tools

Infection often enters through the bark:

• Wounds
• Cracks

Environmental conditions causing stress to plants, such as drought and spring freeze damage, favor disease development.

It often takes years for the infection to spread from the point of infection to the development of cankers and other symptoms.

Symptoms

Typical symptoms occur on stems, branches, and in branch axils.

Common symptoms include:

• Dark, oval or elongated lesions (cankers)
• Dry, sunken lesions with raised margins (edges)
• Surrounding bark discoloration (dark brown to purplish)
• Cankers are often accompanied by resin flow from cracks in the bark
• Reddish to brown, sticky tissue beneath the bark
• Yellow to gray-tan or reddish-brown foliage on infected branches (first symptom noticed)
• Random branch dieback
• Needles that fall off easily when touched
• Multiple cankers can reduce water flow significantly
• Possible tree death if trunk infection occurs

Prevention & Treatment

Environmental stress strongly increases susceptibility to Seiridium infection.

Cultural Controls

• Space trees a minimum of 12 to 15 feet apart to improve air circulation
• Avoid over-fertilization
• Maintain mulch under trees to the drip line (and preferably further) to reduce moisture stress
• Irrigate during drought periods
• Apply water at the soil level to keep foliage dry and reduce disease spread
• If overhead irrigation is necessary, apply in the early morning
• Avoid damage from lawnmowers and string trimmers

Pruning recommendations:

• Prune out and destroy diseased branches promptly
• Cut 3 to 4 inches below the diseased tissue
• Disinfect pruning tools between each cut using:
  • 10% bleach solution (1 part bleach:9 parts water)

Note: Clean and oil pruning tools after using bleach to prevent rust.

Remove and destroy severely affected trees.

Research trials indicate that infected trees may recover when drought stress is reduced with regular irrigation.

Chemical Control

Fungicides are not considered effective or practical for controlling Seiridium canker.

Leyland Cypress Diseases: Phytophthora Root Rot (Phytophthora spp.) on Leyland Cypress

Phytophthora root rot is a soilborne fungal-like disease that affects Leyland cypress growing in poorly drained soils.

Cause

Phytophthora root rot is caused by Phytophthora spp.

• Most common in:
  • Poorly drained soils
  • Compacted soils
  • Sites with excessive moisture
• Pathogen survives in the soil and plant debris
• Infection occurs through:
  • Wounds
  • succulent parts of small roots
• Young plants are most susceptible
• Mature, established trees are seldom affected

Symptoms

Symptoms begin below ground and progress upward.

Common symptoms include:

• Stunted plant growth
• Sparse foliage
• Needle discoloration
  • Yellow
  • Purple
  • Tan
• Progressive decline in vigor
• Root decay and loss of feeder roots
• Cankers at or below the soil line
• Eventual plant death in severe infections

Prevention & Treatment

Management focuses on prevention through proper site selection and improved soil drainage.

Cultural Controls

• Avoid planting in poorly drained soil
• Improve soil drainage by adding organic material to heavy clay soils
• Avoid overwatering
• Select planting sites with adequate water movement

If infection occurs:

• Remove and destroy infected plants, including the entire root system
• Avoid replanting a Leyland cypress where Phytophthora is known to be present
• Select alternative plant species when replanting infected sites

Chemical Control

There is no practical chemical control available for home gardeners.

Leyland Cypress Diseases: Botryosphaeria Dieback (Botryosphaeria dothidea) on Leyland Cypress

Botryosphaeria dieback is a stress-associated fungal disease that causes branch dieback on Leyland cypress.

Cause

Botryosphaeria dieback is caused by the fungus Botryosphaeria dothidea.

• Pathogen overwinters in infected bark and diseased plant tissue
• Spore-producing structures appear as small, raised black dots on cankers
• Spores are spread by:
  • Rain
  • Overhead irrigation
  • Pruning tools
• Infection occurs more readily when trees are stressed

Environmental stresses that increase susceptibility include:

• Drought stress
• Physical injury
• Poor cultural conditions

Symptoms

Symptoms often resemble Seiridium canker but with key diagnostic differences.

Common symptoms include:

• Branches dieback with yellow to brown foliage discoloration (first symptom noticed)
• Needles typically remain attached to recently affected branches
• Deeply sunken V-shaped cankers
• Cankers often girdle stems rapidly
• Bark cracks on affected areas
• Surrounding bark may be darker than on a healthy branch
• Dark brown discoloration beneath bark
• Distinct margin between diseased and healthy tissue
• Botryosphaeria canker may exhibit little or no oozing resin

Prevention & Treatment

Botryosphaeria dieback is strongly associated with plant stress conditions.

Cultural Controls

Follow the same cultural management practices recommended for Seiridium canker:

• Maintain proper plant spacing to improve airflow
• Reduce drought stress through regular irrigation
• Avoid unnecessary pruning wounds
• Prevent mechanical injury to bark
• Avoid excessive fertilization
• Promote vigorous plant growth through proper site selection

Reducing environmental stress significantly decreases disease severity.

Chemical Control

Chemical control is generally not effective for Botryosphaeria canker management.

Leyland Cypress Diseases: Passalora Needle Blight (Passalora sequoiae) on Leyland Cypress

Passalora needle blight is a common fungal disease that causes progressive browning and needle drop on Leyland cypress.

Cause

Passalora needle blight is caused by the fungus Passalora sequoiae.

• Former scientific names include:
  • Cercosporidium sequoiae
  • Asperisporium sequoiae
  • Cercospora sequoiae
• Disease primarily affects foliage that is at least one year old
• Spores develop during late spring through summer
• Spores spread by:
  • Rain
  • Overhead irrigation
  • Wind
  • Pruning tools
• Disease development is often increased by prolonged leaf wetness and reduced airflow within dense plantings.

Symptoms

Symptoms start on lower interior branches and spread outward toward branch tips.

Common symptoms include:

• Browning of older needles
• Needle drop beginning on lower branches
• Symptoms spreading outward toward branch tips
• Progressive upward movement of symptoms in the canopy
• Increased severity from one year to the next
• Green needles remain only at branch tips in severe cases
• Greater disease severity on:
  • North-facing side of trees
  • West-facing side of trees
  • Areas receiving irrigation spray
• Symptoms sometimes resemble drought stress needle drop

Prevention & Treatment

Cultural Controls

• Space trees properly to allow for adequate airflow
• Avoid overhead irrigation when possible
• If overhead irrigation is necessary, irrigate in the early morning hours
• Use drip irrigation when possible
• Maintain adequate irrigation during drought conditions
• Prune and remove infected branches
• Disinfect pruning tools between cuts using:
  • 10 percent bleach solution (1 part bleach:9 parts water)

Drip irrigation hoses should not exceed 75 feet long to avoid excessive pressure loss.

Note: Clean and oil pruning tools after bleach use to prevent rust formation.

Chemical Control

Fungicides may help reduce disease severity when applied preventively.

Active ingredients recommended for homeowner use include:

• Thiophanate-methyl
• Myclobutanil

Applications should:

• begin in late spring
• continue through summer
• ensure thorough spray coverage to runoff
• include inner foliage near the trunk

Achieving adequate spray coverage on large trees is often difficult. See Table 1 for product examples.

Leyland Cypress Insect Pests: Bagworms (Thyridopteryx ephemeraeformis) on Leyland Cypress

Bagworms are common defoliating insect pests that feed on Leyland cypress needles and can cause severe plant decline when populations are high.

Cause

Bagworms (Thyridopteryx ephemeraeformis) are caterpillar larvae that construct protective bags from silk and plant material while feeding on foliage.

Key biological characteristics:

• Larvae construct cone-shaped protective bags from silk and plant debris
• Bags camouflage larvae and protect them from predators
• Adult males are dark-colored, hairy moths with a 1-inch wingspan and clear wings
• Adult females remain inside bags, lack wings or legs, and are yellow maggot-like
• Larvae feed on many shrubs and trees, but prefer conifers (evergreens)

Life cycle characteristics in South Carolina:

• Eggs overwinter inside female bags
• Larvae hatch in May
• Young larvae disperse by wind using silk threads
• Larvae are about 1/8 inch to 2 inches in length, depending on maturity
• Larvae spin their cases, then pupate (transform into an adult) inside them
• Adult male moths emerge in late summer (August/September)
• Adult males locate mates in their bag
• Females lay 500 to 1,000 eggs inside bags before dying

Symptoms

Damage results from feeding by larvae on needles.

Common symptoms include:

• Cone-shaped bags about 2 inches long attached to branches
• Needle loss due to larval feeding
• Reduced plant growth
• Thinning foliage
• Branch dieback in severe infestations
• Heavy infestations can result in plant death

Homeowners often mistake bags for cones or seed structures.

Prevention & Treatment

Management is most effective when populations are controlled early in the life cycle.

Cultural Controls

• Remove bags during winter and early spring
• Destroy removed bags by placing them in a deep container (e.g., 5-gallon bucket)
• Allows beneficial parasitoids to escape from the container when possible
• Monitor plants beginning in spring for newly developing bags

Natural parasites and predators generally suppress populations.

Biological Control

Bacterial insecticides, containing the bacterium Bacillus thuringiensis (B.t.), are most effective on young larvae.

Application guidance:

• Apply when larvae are small (usually in May)
• Repeat applications after two weeks
• Apply sprays in the late afternoon or early evening
• Effectiveness declines significantly once the bags reach ¾ inch in length

B.t. is considered a reduced-risk insecticide option.

Chemical Control

Contact insecticides may be necessary when infestations are severe or when larvae are mature.

Active ingredients to control bagworms include:

• Acephate
• Cyfluthrin
• Cyhalothrin
• Cypermethrin
• Malathion
• Permethrin

Soil-applied systemic neonicotinoid insecticides, such as:

• Dinotefuran
• Imidacloprid

These systemic insecticides provide minimal control (less than 10%) of bagworms and should not be used as a substitute for foliar sprays.

Apply later in the season (May and June) when B.t. is less effective.

Note that contact insecticides also reduce beneficial insect populations (predators and parasitoids) that control spruce spider mites, potentially leading to a spider mite outbreak.

Adequate pesticide coverage becomes difficult once trees reach a significant height.

See Table 2 for examples of products.

Leyland Cypress Insect Pests: Spruce Spider Mites (Oligonychus ununguis) on Leyland Cypress

Spruce spider mites are cool-season mite pests that feed on Leyland cypress needles and cause speckling, discoloration, and needle drop.

Cause

Spruce spider mites (Oligonychus ununguis) are not insects but are closely related to spiders and feed by piercing plant tissue and extracting sap.

Key biological characteristics:

• Very small arthropods are not easily visible to the naked eye
• Feed using piercing-sucking mouthparts
• Prefer conifer hosts such as Leyland cypress
• Considered cool-season mites

Population characteristics:

• Populations peak during spring and fall
• Populations decrease during hot summer weather due to natural predator activity.

Symptoms

Damage results from feeding on needles.

Common symptoms include:

• Tiny yellow speckling on needles (stippling)
• Browning needles
• Needle drop
• Reduced plant vigor
• Fine webbing on foliage during heavy infestations
• Progressive decline with repeated yearly infestations

Prevention & Treatment

Management focuses on monitoring populations and preserving beneficial predators.

Cultural Controls

Encourage natural predators such as:

• Predator mites
• Lady beetles (ladybugs)
• Beneficial insects

Avoid unnecessary insecticide applications that reduce beneficial predator populations.

Wash mites from foliage with a strong spray of water, applying it regularly as needed.

Overuse of insecticides can lead to mite outbreaks by reducing predator populations.

Monitoring Technique

To assess mite populations:

• Hold a white sheet of paper under a branch
• Tap the branch sharply with a pen
• Observe mites crawling around on the paper
• High populations may indicate a need for control

Monitor at 7- to 10-day intervals during peak activity periods (spring and fall).

Chemical Control

Reduced-risk control options include:

• Insecticidal soap
• Horticultural oil
• Neem oil

Other labeled active ingredients include:

• Cyhalothrin
• Malathion
• Tau-fluvalinate

See Table 2 for product examples.

Adequate pesticide coverage may be difficult on tall trees.

Leyland Cypress Insect Pests: Scale Insects (Carulaspis juniperi, Lepidosaphes pallida, Chionaspis minima) on Leyland Cypress

Scale insects are sap-feeding pests that infest Leyland cypress and can cause needle discoloration, branch dieback, and plant decline.

Cause

Scale insects are small, immobile, sap-feeding insects that attach to plant surfaces and extract fluids.

Key biological characteristics:

Adult females are:

• Small
• Immobile
• Lacks visible legs
• Protected by waxy coverings that vary in shape and color depending on species

Adult males are:

• Very small
• Winged
• Mobile

Life cycle characteristics:

• Adult females overwinter on plant surfaces
• Eggs are laid beneath protective coverings in spring
• Crawlers (immature stages):
  • Are mobile
  • Move before settling to feed

Crawlers are the most susceptible stage for control.

Common species affecting Leyland cypress include:

• Juniper scale (Carulaspis juniperi)
• Maskell scale (Lepidosaphes pallida)
• Minute cypress scale (Carulaspis minima)

Symptoms

Damage results from sap removal and plant stress.

Common symptoms include:

• Off-color or dull foliage
• Reduced plant growth
• Yellowing or browning needles
• Branch dieback
• Gradual plant decline
• Potential plant death within 2 to 3 growing seasons if untreated

Symptoms may resemble those caused by spruce spider mites.

Prevention & Treatment

Management depends on targeting the appropriate life stage.

Cultural Controls

• Physically remove scales by scraping them off when infestations are light
• Prune and remove infested branches
• Encourage beneficial insects that naturally suppress scale populations

Biological Control

Natural enemies help regulate scale populations, including:

• Predatory insects
• Parasitoids

Preserving these beneficial organisms improves long-term control.

Chemical Control

Control effectiveness depends on life stage:

Dormant or early-season control (targeting adults):

• Use horticultural oil in late winter or early spring before new growth occurs
• Oil sprays suffocate adult females

Crawler-stage control (most effective timing):

Less Toxic Options

• Horticultural oil
• Insecticidal soap

Synthetic Options

• Acephate
• Cyfluthrin
• Cyhalothrin
• Malathion
• Permethrin

The waxy coating on adult scales protects them from traditional insecticides, making crawler targeting essential.

See Table 2 for examples of products.

Proper pesticide selection and timing are essential for managing Leyland cypress diseases and insect pests.

Leyland cypress diseases and insect pests may be managed with labeled fungicides and insecticides when applied properly and at the correct time. The following tables list active ingredients and example product names for homeowner use.

Fungicides for Leyland Cypress Diseases (Table 1)

Active Ingredient	Example Product Names
Myclobutanil	Ferti-lome F-Stop Lawn & Garden Fungicide Monterey Fungi-Max Spectracide Immunox Multi-Purpose Fungicide Spray Concentrate For Gardens
Thiophanate-methyl	Southern Ag Thiomyl Systemic Fungicide
Note: Chemical control of diseases on large trees is usually not feasible because adequate spray coverage of the foliage with a pesticide cannot be achieved.

Insecticides for Leyland Cypress Insect Pests (Table 2)

Active Ingredient	Example Product Names
Acephate	BioAdvanced Science-Based Solutions 2-in-1 Systemic Rose & Flower Care Granules with 6-9-6 Fertilizer Bonide Systemic Insect Control II
Bacillus thuringiensis (B.t.)	Bonide Thuricide Bacillus thuringiensis (Bt) Garden Safe Brand Bt Worm & Caterpillar Killer Monterey Bt Natural Guard by Fertilome Caterpillar Killer Spray with Bt Natural Guard by Fertilome Caterpillar Killer Spray with Bt Ready to Use Safer Brand Caterpillar Killer For Trees, Shrubs, & Vegetables Concentrate II Southern Ag Thuricide Bt Caterpillar Control Ferti-lome Dipel Dust Biological Insecticide SA-50 Southern Ag Dipel Dus
Cypermethrin	Gordon’s Bug-No-More Lawn & Garden Insect Control Gordon’s Bug-No-More Large Property Insect Control GardenTech Sevin Insect Killer Concentrate GardenTech Sevin Insect Killer Ready-to-Spray
Cyfluthrin	BioAdvanced Science-Based Solutions 24 Hour Lawn Insect Killer Ready-to-Spray BioAdvanced Science-Based Solutions Complete Brand Insect Killer for Soil & Turf Ready-to-Spray I BioAdvanced Science-Based Solutions Insect Killer for Lawns Ready-to-Spray BioAdvanced Science-Based Solutions Rose & Flower Insect Killer Ready-to-Use
Horticultural Oil	Bonide All Seasons Horticulture Spray Oil Ready-to-Use Bonide All Seasons Horticulture & Dormant Spray Oil Ready-to-Spray Ferti-lome Horticultural Oil Spray Monterey Horticultural Oil Concentrate Monterey Horticultural Oil RTU Safer Brand Horticultural & Dormant Spray Oil Concentrate Southern Ag Parafine Horticultural Oil Summit Year-Round Spray Oil
Insecticidal Soap	Bonide Insecticidal Soap Multi-purpose Insect Control Ready to Use Garden Safe Brand Insecticidal Soap Insect Killer Miracle-Gro Nature’s Care Insecticidal Soap Natria Insecticidal Soap Ready-to-Use Natural Guard by ferti-lome Insecticidal Soap Concentrate Safer Brand Insect Killing Soap Concentrate II Whitney Farms Insecticidal Soap 1
Cyhalothrin	Bonide Eight Insect Control Garden & Home II Ready to Use Cutter Backyard Bug Control Spray Concentrate Cyzmic CS Controlled Release Insecticide Martin’s Cyonara Lawn & Garden Insect Control Martin’s Cyonara Lawn & Garden Insect Control Ready-to-Spray Spectracide Triazicide Insect Killer for Lawns & Landscapes
Malathion	Bonide Malathion 50% Insect Control Gordon’s Malathion 50% Spray Hi-Yield 55% Malathion Insect Spray Martin’s Malathion 57% Ortho Max Malathion Insect Spray Concentrate Southern Ag Malathion 50% EC Spectracide Malathion Insect Spray Concentrate Tiger Brand 50% Malathion
Neem Oil	Bonide Captain Jack’s Neem Oil Concentrate Bonide Captain Jack’s Neem Oil Ready to Use Bonide Rose Rx 3-in-1 Concentrate Bonide Rose Rx 3-in-1 Ready to Use Garden Safe Fungicide 3 Garden Safe Fungicide 3 Concentrate Garden Safe Neem Oil Extract Concentrate Monterey 70% Neem Oil Fungicide/Insecticide/Miticide Natria Neem Oil Concentrate Natria Neem Oil Ready-to-Use Natural Guard Brand by ferti-lome Neem Safer Brand Neem Oil Concentrate Fungicide/Miticide/Insecticide Safer Brand Neem Oil RTU Fungicide/Miticide/Insecticide Southern Ag Triple Action Neem Oil
Permethrin	Bonide Eight Insect Control Vegetable, Fruit, & Flower Concentrate Bonide Eight Yard & Garden Ready to Spray Hi-Yield 38 Plus Turf, Termite & Ornamental Insect Control Hi-Yield Lawn Garden Pet & Farm Insect Control Southern Ag Permetrol Lawn & Garden Insecticide Tiger Brand Super 10 Brand
Tebuconazole & Tau-Fluvalinate (miticide)	BioAdvanced Science-Based Solutions 3-in-1 Insect, Disease & Mite Control I
RTS = Ready-to-Spray (hose-end applicator) RTU = Ready-to-Use (pre-mixed spray bottle)Note: Chemical control of diseases and insects on large trees is usually not feasible since adequate coverage of the foliage with a pesticide cannot be achieved.

Pesticide Use and Safety for Leyland Cypress

Pollinating insects, such as honey bees and bumblebees, can be adversely affected by pesticide use. Avoid applying insecticides, fungicides and soil-applied systemic insecticides unless necessary. If treatment is required, apply sprays late in the evening to reduce impact on pollinators.

Always consider less toxic alternatives such as insecticidal soap, horticultural oil, neem oil extract, spinosad, Bacillus thuringiensis (B.t.), or botanical oils. These products can help manage many common pests while reducing harm to beneficial organisms.

Cultural practices are critical for preventing plant diseases. Improve soil before planting, maintain proper plant spacing, apply mulch, apply lime and fertilizer based on soil test results, and avoid frequent overhead irrigation.

Some less toxic fungicides contain sulfur, copper soap, or biological agents such as Bacillus subtilis. For more information about less toxic pesticides, visit HGIC 2770, Less Toxic Insecticides for Garden and Landscape Pest Control in South Carolina.

Always read and follow the label directions on each product. For more information, visit HGIC 2752, Pesticide Application Tips.

Pesticides are updated annually. The last updates were made on 4/26 by N. Jordan Franklin.

Originally published 01/01