A(nother) New Forest Health Concern

  • Close up picture of Beech Leaf Disease infected leaves.

American beech, Fagus grandifolia, is one of the most ubiquitous trees in New Hampshire forests. Because it’s so plentiful and ordinary, rarely achieving the superlatives of other more charismatic species, it’s easy to regard beech with indifference, or in the case of some foresters, even disdain, for its low timber value and tendency to dominate the forest understory and shade out regeneration of other species.

Beech does, however, provide a significant source of food (beech nuts) and valuable habitat (long-lasting cavities in dead beech snags) for wildlife and is an important part of our forest ecosystems. I’ve never personally disliked beech, but I’ve also never been particularly passionate about it either; it’s just kind of there, everywhere, blending into the rest of the forest.

Lately though, I’ve been paying closer attention to beech, looking for signs of a new and potentially quite destructive threat to the future of beech in our forests. Beech trees in New Hampshire have long been affected by beech bark disease, a cankering disease caused by an invasive insect (felted beech scale, Cryptococcus fagisuga, introduced from Europe to Nova Scotia in 1890) and two presumably native fungal pathogens, Neonectria faginata and Neonectria ditissima. Though beech bark disease can and does kill trees, its progression is slow enough that beech has remained a significant component of New England’s forest ecosystems.

Now, beeches face a potentially much more significant threat from beech leaf disease, another non-native species. Beech leaf disease (or BLD, since all the nasty forest pests and pathogens seem to get a three-letter abbreviation) is caused by a microscopic worm-like nematode, Litylenchus crenatae ssp. Mcannii, and potentially its associated fungi or bacteria.

Beech leaf disease is believed to be native to Japan and was detected in Ohio in 2012. By 2019 it made its way east to southwestern Connecticut, and it was first found in Hampshire in 2022. As of the beginning of June, BLD has been found in all seven counties in the southern half of the state and as far north as Center Harbor. Unfortunately, researchers still don’t fully understand how beech leaf disease spreads or how to stop it. While a few treatments may be somewhat effective in bolstering trees’ natural defenses and reducing the nematode population, none have been successfully applied in a forest setting and there are no widely recommended treatments yet. Trees in southern New England seem to be dying quickly (within 3-6 years) after infestation, with the effects of beech leaf disease likely compounded by other stress factors such as drought, winter injury, and other pests and pathogens.

Map indicating southern to central NH locations of Beech Leaf Disease detection. Map by NH Bugs
Map from NH Bugs

Beech leaf disease can be recognized by distinctive bands of darker-colored tissue between the veins of the leaves (often best seen from below), along with curling and distortion of the foliage. The leaves can develop a thick, leathery texture and may drop prematurely. In trees with a heavy nematode infestation, buds may be killed entirely, leading to branch dieback and eventually the death of the tree.

Beech leaf disease nematodes invade beech buds in the summer and fall, then feed and overwinter in the buds causing the damage we see in the spring. Nematode eggs are dispersed in the spring as leaves expand and might be spread by birds, insects, wind, or splashing rainwater.

Detaill of Beech Leaf Disease infested leaves with darker stripes.
BLD banding visible from below, photo from May 2024.
Bands of damaged tissue show up thick and leathery on beech leaves..
Bands of damaged tissue may become thick and leathery. Photo from September 2023.

While beech leaf disease is a significant new forest heath concern, it’s important to know that it’s not the only cause of visible damage to beech leaves. I’ve been seeing some rough looking beech across the state, but it's not all a result of beech leaf disease. A few other organisms causing visible damage to beech leaves this spring include eriophyid mites, aphids, and anthracnose.

Beech erineum mite (Acalitus fagerinea), a type of Eriophyid mite, produces velvety patches of erineum galls that can progress from light green to yellow to rusty-red to dark brown over of the course of the season. Erineum patches can sometimes resemble BLD and they may limit photosynthesis in affected leaves, but the effects on the tree are primarily cosmetic. 

Damage caused by Beech erineum mites can resemble Beech leaf disease damage.
Beech erineum mites.

Anthracnose is a fungal infection that causes black and brown spots and may cause the edges of new beech leaves to curl. Anthracnose is most prevalent when weather conditions are cool and wet during bud-break, which was certainly the case in some parts of the state this spring.

Some species of aphids can also cause leaf curling and damage that resembles the “banding” seen in beech leaf disease.

Leaf damage likely to be caused by aphids.
Likely aphid damage.
Beech leaves with a likely combination of anthracnose, aphid damage, and erineum patches, but does no apparent beech leaf disease.
Beech leaves with a likely combination of anthracnose, aphid damage, and erineum patches, but no apparent beech leaf disease.

 If you see beech leaf disease, especially in a town where it has not yet been detected, please submit a report to NH Bugs, or reach out to your Extension forester if you’re not sure. Beech leaf disease observations in New Hampshire on iNaturalist are also being monitored and cross-referenced with other reporting.

Learn more:

Looking for American Beech (August 2019)

NH Bugs

New Research into Potential Impacts of Beech Leaf Disease (BLD) to Begin at UNH (April 2023)

Have a question about your woods? Contact your Extension County Forester today!

Contact Your County Forester

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