Steps To Monitor Emerald Ash Borer In Delaware Landscapes

Monitoring emerald ash borer (Agrilus planipennis, EAB) in Delaware landscapes requires a structured, repeatable approach. Early detection makes the difference between saving high-value ash trees and losing them to widespread infestation. This article provides a practical, step-by-step monitoring protocol tailored for Delaware’s climate and urban/suburban landscapes, plus guidance on documenting findings, interpreting signs, and making timely management decisions.

Why monitoring matters in Delaware

Delaware has a mix of urban, suburban, and rural landscapes with significant numbers of native ash species (Fraxinus americana, F. pennsylvanica, F. nigra). These trees commonly occur along streets, in parks, and as riparian windbreaks. Emerald ash borer can kill a healthy ash in three to five years after initial infestation depending on tree size and local conditions. Effective monitoring allows property owners, municipal crews, and arborists to:

Detect infestation early when remedial treatments are most effective.
Prioritize trees for preventive treatment or removal based on value and risk.
Coordinate with municipal and state agencies on regulatory or suppression actions.
Document spread and timing to improve long-term landscape planning.

Understand the insect and its signs

Before field monitoring, familiarize yourself with EAB life stages, timing, and the most reliable symptoms.

EAB life cycle and timing in Delaware

Adults typically emerge from D-shaped exit holes in late May through August, with peak adult activity often in June and July depending on spring temperatures.
Females lay tiny, elongated eggs in bark crevices. Eggs hatch into larvae that feed under the bark through the summer and overwinter as late-instar larvae in galleries.
Larval feeding creates S-shaped galleries in the phloem and outer sapwood that disrupt nutrient and water transport.
Depending on local conditions and tree vigor, the life cycle in Delaware tends toward one-year for most populations, but two-year development can occur in colder or marginal conditions.

Key symptoms and signs to look for

D-shaped exit holes, approximately 3-4 mm wide, visible on bark surfaces.
Vertical splits in the bark and visible S-shaped galleries after bark removal.
Canopy dieback, thinning, and sparse foliage, often starting in the upper crown.
Epicormic sprouting (sucker shoots) from the trunk and major branches as the tree reacts to stress.
Increased woodpecker activity or obvious peck marks where birds forage for larvae.
Presence of adult beetles on trunks or foliage during summer, although adults are often difficult to spot.

Preparation: map, prioritize, and equip

Before fieldwork, prepare a plan so inspections are systematic and recorded.

Map ash tree locations on the property using a simple sketch, smartphone GPS app, or property plan. Record species, diameter at breast height (DBH), and tree value (shade, cultural, ecological).
Prioritize trees: high-priority = large, healthy ash on streets, near structures, or with high aesthetic/heritage value; moderate = medium-sized yard trees; low = small or declining ash with little landscape value.
Assemble monitoring equipment: binoculars, headlamp or flashlight, hand lens (10x), increment borer or diameter tape for DBH, camera (smartphone), permanent marker and notepad, ladder or pole pruner for canopy inspection if safe, and personal protective equipment (gloves, eye protection).
Coordinate with neighbors or municipal crews if monitoring public trees, and note any local quarantine or regulatory reporting requirements.

Routine monitoring schedule and techniques

A consistent schedule increases the chance of early detection and provides baseline records for comparison.

Timing and frequency

Conduct initial baseline inspections in late spring (May-June) to catch adult emergence and early canopy symptoms.
Repeat inspections mid-summer (July) and late summer/early fall (August-September) to detect increasing dieback and exit holes.
Conduct a winter inspection (December-February) focused on woodpecker damage, bark splits, and epicormic shoots, when foliage is absent and bark symptoms are easier to see.
For high-priority trees, inspect every 2-3 months during the active season and once in winter.

Systematic visual inspection steps

From a safe distance, visually assess overall canopy condition and note thinning, dieback percentage, and any epicormic sprouting.
Walk the trunk and lower scaffold branches, inspecting for D-shaped exit holes, bark splitting, and woodpecker activity.
Use binoculars to inspect the upper crown for dead branches, thinning at the top, or adult beetles on foliage.
Check the root collar and lower trunk for suckering, staining, or crown dieback indicators.
Photograph any suspect signs with scale (ruler or coin), record location, tree DBH, and date for later comparison.

Active detection methods used in Delaware landscapes

Alongside visual inspection, several active techniques increase detection likelihood. Many are used by state and municipal programs; adapt them for property-level monitoring.

Purple prism traps and sticky panel traps: these attract adult beetles and are typically deployed by regulatory agencies. If you participate in community monitoring programs, learn proper placement (height, orientation) and deployment timing.
Bark peeling and bark scrapes: on a small, representative area, carefully remove a section of loose bark to look for larvae and galleries. Do this only when necessary and in a way that minimizes damage.
Girdled or trap trees: intentionally girdled or felled trap trees can attract egg-laying adults; agencies use them for detection and monitoring. Girdling should be performed only by trained personnel and with appropriate permission.
Sticky tape or banding: not generally recommended as a long-term solution because non-target catch and limited detection sensitivity; consult extension guidance before use.

Interpreting findings and making decisions

A structured decision framework helps translate monitoring results into actions.

No signs detected and tree healthy: continue routine monitoring on schedule; consider preventive insecticide treatments for high-value trees if EAB is known in your county or nearby counties.
Early signs (sparse canopy, small percentage of dieback, few exit holes): contact a certified arborist or your county extension agent to confirm. If confirmed, develop a treatment plan or removal schedule.
Widespread upper canopy mortality, many exit holes, or heavy woodpecker damage: tree is likely heavily infested. Prioritize removal for safety and plan for replacement with non-ash species.
Multiple positive findings across properties: notify local agricultural or forest health authorities so they can coordinate surveys, regulatory responses, and public outreach.

Treatment and preventive considerations (practical takeaways)

Monitoring connects to treatment decisions. Below are practical takeaways for property owners.

Early preventive treatments with systemic insecticides (e.g., emamectin benzoate injection, dinotefuran trunk sprays or soil injections) are most effective when applied before significant canopy loss. Emamectin benzoate injections often provide multi-year control in one injection.
Timing matters: apply soil-applied systemic insecticides in early spring when soils are thawed and roots are active. Trunk injections are commonly done in late spring to summer depending on the product.
Treatments are a commitment: regular re-treatment intervals vary by product (annual to every 2-3 years). Keep records of product, date, and application method.
Removing infested trees reduces local borer pressure. Consider prompt removal of heavily infested trees and proper disposal of wood (chipping, burning where allowed) to minimize spread.
Replant with diverse, non-ash species to reduce future pest vulnerability. Favor native species adapted to local site conditions.

Documentation, reporting, and working with agencies

Good records and collaboration improve statewide detection and response.

Keep a monitoring log with photos, dates, DBH, symptom descriptions, and GPS or street addresses for each tree.
If you suspect EAB, report findings to your county extension or state agriculture/forestry office. Provide clear photos of exit holes, galleries (if exposed), and overall canopy condition.
Participate in community detection programs or citizen science initiatives if available. Local municipalities often coordinate surveys and can supply traps or technical assistance.
Be aware of state regulations or quarantines regarding movement of ash wood; moving firewood can spread EAB long distances.

Safety and practical tips for field monitoring

Do not climb trees or perform risky inspections without professional training and equipment. Use binoculars and ground-level methods when possible.
When peeling bark or using tools, wear gloves and eye protection. Limit invasive inspections to minimize tree damage.
If felling or removing trees, hire a licensed arborist familiar with EAB protocols and local regulations.
Coordinate with neighbors and public agencies before treating or removing trees that border public rights-of-way.

Final checklist for Delaware landscape monitoring

Map and prioritize ash trees on your property.
Inspect trees late spring, mid-summer, late summer, and once in winter.
Look for D-shaped holes, S-shaped galleries, canopy thinning, epicormic shoots, and woodpecker damage.
Photograph and document findings with date and location.
Report confirmed or suspected EAB to local authorities.
Consult a certified arborist about treatment options for high-value trees and removal for heavily infested trees.
Replant with diverse, non-ash species to improve landscape resilience.

Consistent, informed monitoring is the best defense against emerald ash borer in Delaware. With routine inspections, good records, and timely coordination with professionals and authorities, property owners and land managers can slow spread, preserve valuable trees, and plan for resilient, ash-diverse landscapes.