Beech Leaf Disease on the Main Line

A mid-April article in The Philadelphia Inquirer titled “Beech Leaf Diseases is Killing Trees in Pennsylvania and N.J.” was very concerning for customer’s with valuable Beech trees in their landscapes. Thank you to everyone that forwarded the Inquirer article and other subsequent news coverage.

Our busy season has just died down and I now have the opportunity to share my current approach to protecting my customer’s trees from this new threat.

What is Beech Leaf Disease (BLD)?

BLD is an invasive pest that affects a variety of Beech trees including our native, American Beech (found growing in PA’s forests), as well as Copper Beech and European Beech, which are also staples in the Main Line landscape.

The pest was first discovered along Lake Erie in Ohio in 2012. By 2021-2022 growing season, it had been sighted in nearly every single county in Pennsylvania, including the five counties surrounding the Main Line (Bucks, Chester, Delaware, Montgomery and Philadelphia).

BLD can kill Beech trees in 2-7 years, with younger trees dying more quickly than mature trees.

Although researchers have been working to understand this pest for nearly a decade, little is still known. So far, scientists have concluded that BLD is caused by a microscopic worm called a nematode (pictured below). The nematodes overwinter in the leaf buds of Beech trees. When the season’s news leaves emerge in Spring, they appear severely deformed and drop prematurely.

What makes BLD more complicated is the apparent overlap of fungal and bacterial agents in the foliar samples that have been studied. This has led researchers to question whether the mere presence of nematodes is enough to cause tree decline or if other fungi and bacteria contribute to BLD.

Current Treatment Plan

Keeping in mind that researchers still have much to understand about this disease, and that widescale studies on the efficacy of any product have yet to be conducted, some promising treatments have emerged to protect the Beech in our residential landscapes.

I have been in contact with the team at Rutgers University Plant Diagnostic Laboratory, as well as the team at Penn State’s Agriculture Extension to learn about the latest in experimental treatments. Promising research out of the University of Rhode Island has found Beech treated 2x per year with phosphite-based soil drenches were significantly healthier with fewer nematodes than untreated trees.

A second treatment showing early success is a spray treatment of fluopyram, a combination fungicide and nematicide. In one study, trees treated with fluopyram showed a 40% reduction in canopy symptoms the year following treatment.

I am pleased to offer both treatments above to my customers. Please note: fluopyram is not an organic product. While I strive to use OMRI-listed (most of which are used by organic farmers and are safe for same day harvest and consumption) products when spraying, the serious threat of BLD to our Beech is reason to make an exception.

Finally, as we know from Manion’s “spiral of decline,” healthy trees are better able to withstand disease and insect pressure. In addition to the two treatments above, I am recommending routine, annual fertilizer treatments for all valuable Beech trees in the landscape. This has been a very bad year for Woolly Beech Aphid, a white, fuzzy insect that is found on the underside of Beech leaves. Heavy populations (as I have seen this year) can weaken the Beech trees. Thus, I have been using OMRI-listed insecticides to manage Woolly Beech Aphids on my customers’ trees in order to mitigate stressors and keep the Beech as healthy as possible.

If you have a Beech tree in your landscape that you are concerned about, please reach out to schedule a consutlation.