Beech Leaf Disease Is Spreading Fast! Here’s How to Respond

Pennsylvania’s woodlands have endured a series of devastating tree losses over the past century. American chestnuts were nearly wiped out by blight. Dutch Elm Disease decimated native elms. Emerald Ash Borer has left entire forests without a single living ash tree. Now, a newer and fast-moving disease is threatening another cornerstone of our forest ecosystem: the American Beech.

Beech Leaf Disease (BLD) is spreading rapidly across southeastern Pennsylvania, and its impact is already being felt. We’ve observed widespread symptoms this season in locations throughout the Main Line, including Villanova, Bryn Mawr, Wayne, Devon, and Philadelphia itself. As arborists, we’re very concerned about what this means for our native landscapes, urban trees, and the wildlife that depend on beech.

What is Beech Leaf Disease?

Beech Leaf Disease is caused by a microscopic nematode (Litylenchus crenatae mccannii) that invades the leaf tissue of American Beech (Fagus grandifolia) as well as European Beech varieties (Fagus sylvatica). The nematodes feed throughout the growing season, fall, and winter. By the time the tree’s leaves expand in spring, the damage has already been done

Infected trees show:

• Dark, thickened bands between leaf veins (most visible when viewed from below)
• Curling or distortion of leaves
• Thinning canopies and reduced leaf-out
• Premature leaf drop

These symptoms typically appear in late spring and early summer, following infection from the previous year.

Healthy Beech vs. Infected Beech

Visual symptoms are one of the best tools we have for early detection of BLD. While healthy beech leaves are smooth, symmetrical, and evenly green, infected leaves show distinctive signs that can often be spotted even from a distance.

Trait	Healthy Beech	Infected Beech
Leaf color	Uniform green	Dark, thick bands between veins
Leaf shape	Flat, symmetrical	Crinkled, curled, or leathery
Canopy	Full, dense	Thinning or sparse
Timing	Leaves emerge normally in spring	Delayed or stunted leaf-out

Why It Matters

Beech trees are a cornerstone species in many of Pennsylvania’s forests and urban landscapes. Their nuts provide critical food for wildlife, and their smooth gray bark and winter foliage (known as marcescence) make them both iconic and valuable.

BLD has the potential to severely reduce beech populations, just as Dutch Elm Disease and Emerald Ash Borer have devastated elms and ashes.

Without intervention:

• Young beech trees (under 20 inches DBH) can die in as little as 1 to 2 years.
• Mature trees (over 20 inches DBH) may survive for 6 to 10 years, but will steadily decline in health and vigor.

How Does It Spread?

Beech Leaf Disease was first identified in Ohio in 2012. Since then, it has spread to much of the northeastern United States and parts of Canada. It is now confirmed in all 67 counties in Pennsylvania.

The nematodes are believed to spread through several means, including rain, wind, insects, birds, and possibly through human activity such as moving contaminated soil or using unclean pruning tools.

One of the biggest challenges is timing. Infection often isn’t visible until the following spring, when the damaged buds begin to leaf out. As a result, many trees that appear healthy this year may already be infected and will show symptoms next spring.

Treatment

Research into BLD is ongoing, but one treatment has emerged as the most effective: Trunk-injected Thiabendazole hypophosphite (Arbotect® 20-S)

According to Rutgers University’s most recent forestry guidance, this macro-infusion treatment is the leading option for controlling BLD in landscape trees. It’s the same formulation used to treat Dutch Elm Disease, and it has shown promise in suppressing nematode populations in beech trees.

Treatment highlights:

• Application window: June–July (every other year)
• Longevity: Provides up to two years of protection
• Method: Systemic trunk injection — no sprays or drift
• Research-based: Recommended by Rutgers Cooperative Extension and other leading plant pathology programs

Other options, such as foliar sprays or soil-applied fungicides, have shown mixed or inconsistent results. At this time, trunk injection with Arbotect® 20-S is the only method with consistently strong performance.

What You Can Do Now

If you have beech trees on your property, even those that appear healthy, we strongly encourage proactive care. Early treatment provides the best chance of maintaining tree health before the nematode population becomes too established.

Here’s what you can do:

• Schedule an evaluation: Our team can assess your trees and determine if treatment is appropriate.
• Get on the calendar early: June and July are the optimal months for treatment.
• Monitor annually: Even healthy-appearing trees may be infected. Catching BLD early increases the chance of long-term preservation.
• Stay informed: Research is evolving, and we stay up-to-date with the latest recommendations from Penn State, Rutgers, and other forestry institutions.

Beech trees are too valuable to lose without a fight. With early detection and the right treatment plan, we can help preserve these iconic trees for future generations.

For questions, consultations, or to schedule treatment, reach out to the team at Champion Tree & Plant Health Care.