About Invasive Plants and Insects

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.

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. These threats impact biodiversity, public safety, and long-term forest resilience.

Invasive & Significant Insects

Insects listed here are categorized by their feeding strategy. Boring insects are the most lethal as they girdle trees internally, while defoliators deplete energy reserves over time.

Wood-Boring Insects (Highest Mortality Risk)

Emerald Ash Borer (EAB): EAB attacks all native Ash, causing D-shaped exit holes and serpentine galleries. Trees affected by EAB die within 3-5 years.
Southern Pine Beetle (SPB): SPB attacks Pitch Pine and hard pines, causing small pitch tubes on bark. It can kill groups of trees rapidly through mass attacks.
Asian Longhorned Beetle (ALB): ALB is a high-risk wood-borer attacking Maples and hardwoods. It is not yet widespread in CT but it is a major threat in nearby areas of New England.

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: (Native) Attacks stressed Oaks post-drought.

Tree Diseases

Diseases occur when a susceptible host, a pathogen and a conducive environment overlap. The following diseases are organized by its 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. The plants below are a few notable invasives in CT. You can find out more information, or 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 thus 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. Fragmentation fundamentally changes the "defense system" of a forest. When a continuous forest is broken into smaller pieces, it creates more edge habitat, which serves as a primary entry point for invasive plants.

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. Ask "Why is this tree susceptible?" You can improve its conditions through mulching, irrigation and soil aeration before using chemicals, but if you start seeing signs of disease or impact by an invasive threat, consider looking for help through the following.

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.