About Invasive Plants and Insects

CT Department of Energy and Environmental Protection (DEEP) and UConn monitor factors influencing forest health. Our forests face pressures from invasive species, emerging diseases, and forest fragmentation, which impact biodiversity, public safety, and long-term forest resilience.

The following short guide is loosely based on CT DEEP's Threats to CT Trees and Forest Health. For photos and further details, please refer to that webpage. For educational and outreach resources relating to this topic, view our Extension Forestry (English and Spanish) brochure series instead, which offers non-invasive planting alternatives to common ornamental invasive species.

Invasive & Significant Insects

Insects listed here are categorized by their feeding strategy. Boring insects are the most lethal, while defoliators deplete energy over time.

Wood-Boring Insects (Highest Mortality Risk)

  • Emerald Ash Borer (EAB): Attacks all native Ash; trees die in 3-5 years.
  • Southern Pine Beetle (SPB): Attacks Pitch Pine and hard pines; can kill groups rapidly.
  • Asian Longhorned Beetle (ALB): High-risk borer attacking Maples and hardwoods; not yet widespread in CT.

Defoliators, Sucking Insects & Others

  • Spongy Moth: Defoliates Oaks; repeated attacks cause carbon starvation.
  • Hemlock Woolly Adelgid: White "wool" sacs; causes needle loss in Hemlocks.
  • Spotted Lanternfly: Sucking insect; produces honeydew and sooty mold.
  • Winter Moth: Spring defoliator of Maples and fruit trees.
  • Jumping Worm: Alters soil structure and prevents regeneration.
  • Twolined Chestnut Borer: This native insect attacks stressed Oaks post-drought.

Tree Diseases

Diseases occur when a susceptible host, pathogen, and conducive environment overlap. The following diseases are organized by their most noticeable impacts on trees.

Vascular Wilts & Blights

  • Oak Wilt: Rapid canopy wilt (High Priority).
  • Chestnut Blight: Historically reshaped CT forests.
  • Dutch Elm Disease: Invades xylem, blocking water.
  • Beech Leaf Disease: Emerging threat to Beech.

Foliar & Structural

  • Anthracnose: Common leaf spot; often cosmetic.
  • Beech Bark Disease: Complex of insect and fungi.
  • Verticillium Wilt: Soil-borne vascular disease.
  • Root Rots: Compromise structural stability (Conks).

Invasive Plants

Non-native plants outcompete native vegetation, limiting tree regeneration and reducing biodiversity. You can report invasive plants through the CT Invasive Plants Working Group.

Japanese Barberry (Berberis thunbergii)

A significant concern in CT, Japanese Barberry creates dense thickets that increase tick abundance and the risk of Lyme disease.

Other Major Invaders in CT:

  • Oriental Bittersweet
  • Multiflora Rose
  • Burning Bush
  • Tree-of-Heaven
  • Norway Maple
  • Autumn Olive
  • Garlic Mustard

Forest Fragmentation

Fragmentation is the separation of forest into smaller, isolated parcels. Unlike weather disturbance, fragmentation is often permanent and prevents the forest from restoring its former characteristics.

Causes: Roads, agriculture, utility corridors, and subdivisions.
Resource: The UConn CLEAR website provides town-by-town mapping of these trends.

Promoting Healthy Habitat & Connectivity

Your yard is part of Connecticut's forest. Many invasive plants originally arrived in Connecticut through landscaping, but making small choices in your plant selection creates a big impact. Invasive plants do not just displace native ecosystems—they are also often highly susceptible to invasive insects (for example, Tree-of-Heaven strongly attracts and hosts the Spotted Lanternfly). By planting Connecticut native species instead of invasive ornamentals, you enhance habitat connectivity, support local pollinators, and strengthen forest resilience against pest outbreaks.

Benefits of Choosing Natives

  • Support Pollinators: Essential for local wildlife and plant life cycles.
  • Provide Wildlife Habitat: Restores natural ecological networks.
  • Maintain Healthy Forests: Reduces pressure from invasive insects and diseases.
  • Protect Water Quality: Enhances soil stability and natural filtering.
  • Increase Climate Resilience: Helps native species adapt to changing conditions.

Native Alternatives to Plant Instead

Replace invasive landscape plants with these Connecticut alternatives:

  • Black Gum (Nyssa sylvatica) instead of Tree-of-Heaven
  • Red Maple (Acer rubrum) instead of Norway Maple
  • Highbush Blueberry or Virginia Rose instead of Japanese Barberry
  • Serviceberry (Amelanchier canadensis) instead of Autumn Olive
  • Virgin's Bower (Clematis virginiana) instead of Oriental Bittersweet

How to Help & Manage

Plant Health Care (PHC)

Management begins with diagnosis. Improve conditions through mulching, irrigation, and soil aeration. For signs of disease or invasive threats, consider help from:

The Management Hierarchy

  • Cultural: Site improvement.
  • Mechanical: Pruning or egg mass removal.
  • Biological: Protecting natural predators.
  • Chemical: Targeted and only when necessary.

A Few Tips to Keep in Mind

  • Don't Move Firewood: Burn it where you buy/cut it.
  • Clean Your Gear: Wash boots and tires after outings.
  • Go Native: Replace invasive ornamentals with native alternatives.
  • Monitor Your Forest: Report unusual tree damage or insect sightings.