Breaking Down Beech Leaf Disease

Dane Buell is the past chairman of the ANSI A300 committee and TCIA representative. With over 30 years of experience, Buell holds several leadership roles in the tree care industry.

In recent years, Beech Leaf Disease (BLD) has emerged as a significant threat, causing alarming tree mortality rates across the Midwest, Northern Mid-Atlantic, and Northeastern states. This condition primarily targets American beech, European beech, and other non-native beech species, resulting in dark striping on leaves, leaf distortion, and ultimately death if untreated. With its rapid spread and management challenges, I sought insights from leading industry experts Matthew Borden, DPM, Research Scientist at Bartlett Tree Research Laboratories, and Rich Cartier, Northeast Territory Manager at Rainbow Ecoscience.

Background on Beech Leaf Disease

What causes BLD?

Beech Leaf Disease is caused by the foliar nematode Litylenchus crenatae. Intrigued by the term “disease,” I asked Borden why we describe BLD as such, given that pathogens (fungi, bacteria, viruses) typically define disease in arboriculture.

“Nematodes and disease pathogens are often combined from a research and scientific perspective due to the ongoing stress they cause in affected plants, Borden explained. However, in this instance, the causal agent of BLD was identified after the condition was named, making its name ironically accurate but somewhat confusing.”

As an experienced practicing arborist, I had never heard of a foliar nematode before. Both Cartier and Borden confirmed that similar tree pest problems are known in our industry. For instance, foliar nematodes in the Aphelenchoides group attack many popular landscape perennials. Pine Wilt Disease, caused by the pine wood nematode Bursaphelenchus xylophilus, is another tree-killing nematode that affects non-native pine trees, but outbreaks are reportedly easier to get under control.

Where did BLD originate?

The origins of BLD trace back to Japan. Recently, a team of U.S. researchers visited Japan to understand why beech trees there seem less affected. Borden noted that there appears to be a lack of natural predators that could regulate nematode damage. Rather, the U.S researchers have observed that in Japan, beech trees quickly shed leaves showing early stages of BLD, likely serving as a defense response to minimize damage and keep nematode populations low.

The Complexity of Beech Leaf Disease

While many fatal tree conditions stem from a complex web of problems, both Cartier and Borden emphasized that BLD is indeed a distinct issue. Beech trees have faced challenges like Beech Bark Disease, Phytophthora, and cultural problems including over-pruning and soil compaction for years. However, BLD uniquely leads to carbohydrate starvation, which makes it a particularly fatal condition.

Living in the Northeast, I personally perceive BLD as a fast-moving, acute issue rather than a chronic one, as seen in the Midwest. To this, Borden agreed, remarking that he, too, does not fully understand why BLD appears to progress more rapidly in this region — my observations indicate that beech trees can succumb to BLD within just two growing seasons.

Management Strategies

What Treatment Protocols are currently being prescribed?

Through my discussions with Cartier and Borden, it became clear that a decisive management approach is necessary. Cartier revealed that many companies perform both spring and fall foliar applications of a fluopyram-containing product. The only such product currently labeled for BLD is Broadform, which is a combination of fluopyram and trifloxystrobin, applied at a rate of 4-8 fl. oz. per 100 gallons, with a yearly limit of 27.3 fl. oz. per acre. Be cautioned that some arborists have been confused by the differing re-entry requirements for agricultural versus horticultural uses. Bartlett researchers, who discovered this treatment in 2022 and applied for the special use labels, are continuing to fine-tune dosage and application timing.

Moreover, Cartier noted some arborists continue to apply phosphites to the soil or lower trunk, as these compounds can manage Phytophthora and improve tree vigor, although results with phosphites alone can vary significantly.

Borden elaborated on Bartlett Tree Expert Company’s protocol, noting they use Broadform on trees smaller than 8 to 10 inches in diameter that can be sprayed from the ground with full coverage, and Arbotect 20-S systemic treatments for larger trees. He also shared that, based on their recently published research done in collaboration with Rainbow Ecoscience, they have adjusted their application timing, now recommending that injections should be most effective if made between mid-June and mid-July.

Conclusions

Considering the novelty and rapidness of this fatal pest problem, we must act quickly and consistently. Time is of the essence, as our ability to stay ahead of this issue diminishes constantly. Unfortunately, a major USDA investment in managing BLD seems unlikely due to its relatively small economic impact, despite its substantial environmental consequences.

A consistent management approach is crucial for maintaining consumer confidence. If consumers encounter conflicting treatment protocols, their trust in our recommendations may diminish. While I remain hopeful for European beech trees in managed landscapes, our native American beech populations are in serious jeopardy here in the Northeast. The overwhelming damage I witnessed in Southern Rhode Island last summer underscores the need for immediate action. For anyone operating in states affected by BLD, prioritizing consistent communication of management options in 2025 is essential.

As we navigate these challenges, collaboration and proactive measures will be our best tools in combating Beech Leaf Disease.