Beech leaf disease is the latest threat to our urban forest (Sponsored)

AI illustration (ChatGPT/Bill Eck)

This article is sponsored by Bartlett Tree Experts.

by Bill Eck, Board Certified Master Arborist

If you’ve lived in the DC area long enough, you’ve witnessed major changes to our neighborhood canopy.

More than a decade ago, the emerald ash borer swept through and quietly removed most of the green and white ash trees from our streets and backyards. A few survived — but only because their owners committed to consistent treatment.

More recently, we experienced what many came to call “oak decline.” Mature oaks in landscapes (less so in forested settings) struggled and many were lost. Again, survival often came down to early intervention and intensive care.

Now, a new threat has arrived: beech leaf disease, or BLD.

Our abundance of beech trees is under threat

American beech dominates the National Park Service portion of the urban forest in DC, constituting the most abundant tree by stem count. These trees are a defining feature of our parklands and private landscapes.

If left untreated, beech leaf disease is not a cosmetic issue. Research shows that in eastern North America, healthy beech trees die within three years after symptoms begin.

The parklands may look very different in a decade. But trees on private property do not have to follow the same trajectory.

What is beech leaf disease?

BLD is caused by a microscopic foliar-feeding nematode (a tiny roundworm) called Litylenchus crenatae mccannii.

The nematodes infest leaves during the growing season, then migrate into buds for the winter. By spring, damage is already present as the leaves emerge.

Over successive years, the disease disrupts the tree’s ability to photosynthesize effectively. Leaves become thickened, leathery, puckered and chlorotic. Bud death and twig dieback follow.

Eventually, the tree becomes stressed and vulnerable to secondary problems such as borers, Phytophthora and fungal cankers. The final outcome is always death.

Visible banding in the foliage is an early sign of beech leaf disease infection. (Bartlett Tree Experts photo)

What to look for

Early symptoms often start low in the canopy and move upward. Key signs include:

• Dark green striping between leaf veins
• Interveinal yellowing or chlorosis
• Leaves that appear cupped or puckered from the top
• Thickened, leathery foliage as the disease progresses

These symptoms can be confused with mite galls or aphid damage, so proper diagnosis is important.

Is there a treatment?

Yes — and this is where the story differs from what we’re seeing in unmanaged forests.

Research trials have produced two primary management programs:

1. Foliar applications for small to medium trees and hedges, applied mid-summer through early fall during peak nematode activity.
2. Root flare injection treatments for medium to large trees and trees near sensitive waterways, typically implemented by mid-summer. Research indicates that a single injection can provide significant suppression of BLD symptoms for two seasons

These treatments are designed to reduce nematode populations at a critical stage in their life cycle and limit migration into overwintering buds.

In addition, soil applications of potassium phosphite products can support tree health by enhancing resistance and slowing disease progression. While not a cure, these cultural and soil health measures are important components of a comprehensive management plan.

Timing matters

One of the most important takeaways from current research is that timing is critical. Treatments this year will suppress nematode populations and damage symptoms in 2027.

Once the optimal treatment window has passed, waiting until the following season may be necessary for best results.

What property owners can do now

1. Identify whether you have a beech tree. American beech has smooth gray bark and simple leaves with straight, parallel veins that give the leaf a ribbed appearance.
2. Inspect for early striping or puckering this spring and summer.
3. Consult a qualified arborist early. As we learned with ash and oak decline, proactive care dramatically changes outcomes.

The DC area has always been defined by its trees. While the broader forest ecosystem will likely shift over time, trees on private property can be preserved with informed and timely management.

We cannot stop every emerging pest or disease. But we can choose not to lose our beech trees without a fight.

If you have a beech tree (or you aren’t sure) and would like to discuss treatment options (or would like to discuss any other tree-related issues), please reach out to Bill Eck at beck@bartlett.com