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.

This 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.

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.

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.