Protecting Beech Trees from Leaf Disease and Bark Disease

If you have a mature beech on your property — American, European, or one of the ornamental cultivars like copper or weeping beech — there are two diseases you should know about. Both are now present in New York, both can kill the tree if left alone, and both respond to treatment when caught early. We treat for both as part of our Plant Health Care program.

 Beech Leaf Disease

Beech Leaf Disease, or BLD, is caused by a microscopic nematode (Litylenchus crenatae mccannii) that lives in the buds and leaves. It was first identified in Ohio in 2012, spread into New York shortly after, and is now widespread across the state. It moves fast — faster than most professionals in our field expected.

The earliest sign is dark interveinal banding on the leaves, usually visible from below when you look up into the canopy in spring. The bands look almost like someone drew on the leaf with a marker between the veins. As the disease progresses, leaves become leathery, curled, and undersized. The tree pushes a second flush of paler, weaker leaves to compensate, which depletes its reserves. Within a few years, canopy thinning and branch dieback set in, and the tree begins a steady decline.

There is no cure, but there is an effective treatment. Research out of the Connecticut Agricultural Experiment Station and the University of Rhode Island has shown that potassium phosphite — applied either as a basal bark spray or a soil drench — significantly reduces symptoms and protects the tree. The phosphite works by stimulating the tree's own defense response rather than killing the nematode directly. For larger or higher-value trees, trunk injection with a phosphite product is also an option and is often the most efficient delivery method on a mature beech.

Treatment is applied during the growing season, typically with two applications spaced about a month apart between May and August. Trees that are caught before significant canopy loss tend to do well on this program. Trees in late-stage decline can sometimes be stabilized, but the goal shifts from full recovery to managing the timeline.

Beech Bark Disease

Beech Bark Disease, or BBD, is a different problem with a different cause. It's a two-part attack: first, a tiny sap-feeding insect called beech scale (Cryptococcus fagisuga) colonizes the bark, creating thousands of small feeding wounds. Then a fungus — usually Neonectria faginata or N. ditissima — moves in through those wounds and starts killing the inner bark and cambium.

The first thing most people notice is what looks like a fuzzy white coating on the trunk, especially in cracks and rough bark. That's the wax the scale secretes to protect itself. Later, you'll see small reddish-brown weeping spots where the fungus is active, and over time, sunken cankers and bark splitting. Heavily affected trees can develop what foresters call "beech snap," where the trunk fails structurally above a canker, sometimes well before the tree shows full crown decline.

Treatment works in two parts because the disease has two parts. We target the scale with a systemic insecticide or horticultural oil, depending on the tree and the season. For the fungus, we use a phosphite trunk drench in spring, and sometimes a second application in fall, to boost the tree's defense response and limit canker expansion. On smaller trees, mechanical removal of the scale with a stiff brush and water is part of the program. On large trees, that's not practical, and we go with the systemic approach.

Beech Bark Disease is best treated before the fungus is well established. Once large cankers and significant cambial death are present, the tree is harder to save, and at that point a risk assessment for nearby structures and walkways becomes part of the conversation.

When to Call Us

If you have a beech and you've noticed any of the following, it's worth a site visit:

• Dark striping between the veins on the leaves, visible in spring or early summer
• Leaves that look curled, leathery, or smaller than they should be
• A thinning canopy, dead branches at the top, or bare spots that weren't there last year
• White woolly patches on the bark
• Reddish weeping spots, sunken areas, or splitting bark on the trunk
• Root sprouts forming a thicket around the base of a declining tree

Mature beeches are slow-growing, long-lived trees that are difficult and expensive to replace at any meaningful size. A specimen beech on a residential property is often the most valuable tree in the landscape. Our ISA-trained arborists will do a full diagnostic on site, confirm what's going on — sometimes both diseases are present on the same tree, sometimes the symptoms are from something else entirely — and put together a treatment plan that matches the tree's condition and your goals for the property.

Call us to schedule a beech evaluation, or ask about adding beech protection to an existing Plant Health Care agreement. 

Protecting Boxwoods from Box Tree Moth, Blight, and Other Problems

Boxwoods do a lot of structural work in a landscape — hedges, foundation plantings, formal gardens, parterres. They're also under siege from a list of pests and diseases that has gotten longer in the last few years, with the arrival of box tree moth in New York adding a serious new threat to the existing lineup of leafminer, boxwood blight, and Volutella blight. We treat for all of these as part of our Plant Health Care program.

Box Tree Moth

Box tree moth (Cydalima perspectalis) is an invasive caterpillar from East Asia that was first detected in the United States in Niagara County, New York, in 2021. It has since spread across western New York and into neighboring states, and the federal quarantine area has continued to expand. It is the most aggressive boxwood pest currently on the landscape — a heavy infestation can defoliate a hedge in a matter of weeks, and the larvae will sometimes strip the bark on stems once the leaves are gone, killing the plant outright.

The larvae are green with black stripes and a shiny black head. Early stages feed on the underside of leaves and are easy to miss; by the time you see the webbing and the bare twigs, you're already well into the problem. There are two to three generations per season in our area, so an untreated planting can get hit repeatedly through the summer.

Treatment is straightforward when caught at the right life stage. We use targeted insecticide applications timed to the larval feeding windows, with options ranging from Bacillus thuringiensis (Btk) on smaller or organically managed plantings to systemic and contact products for heavier infestations. Pheromone trapping helps us track adult flights and time applications precisely. Properties in known infested areas benefit from a monitoring program rather than waiting for visible damage.

One note on regulation: because the federal quarantine restricts movement of boxwood material out of affected counties, debris and prunings from infested plants need to be handled correctly. Our crews follow the current quarantine protocols on every job.

Boxwood Leafminer

Boxwood leafminer (Monarthropalpus flavus) is a small orange fly whose larvae tunnel inside the leaves, causing blistering, yellowing, and premature leaf drop. It's been here a long time — likely since the 1600s — and it's been called the most destructive insect pest of landscape boxwoods. Heavy infestations weaken plants and make them more vulnerable to the diseases discussed below.

The damage looks like raised tan or yellow blisters on the underside of the leaves, and if you hold a leaf up to the light, you can sometimes see the larvae inside. Adult flies emerge in spring in a brief swarm, often noticed because they collect in spider webs near the plants.

We control leafminer with well-timed insecticide applications, either targeting the adults during their short emergence window or using systemic products that reach the larvae inside the leaf. Timing matters more than product choice — too early or too late and you miss the window.

Boxwood Blight

Boxwood blight (Calonectria pseudonaviculata) is a fungal disease that causes dark leaf spots with darker borders, black streaking on green stems, and sudden, severe leaf drop. The defoliation is the giveaway — Volutella blight kills leaves but they tend to hang on, while boxwood blight knocks them off the plant rapidly. The fungus survives in fallen leaf debris for years, which makes sanitation a critical part of any program.

There is no cure once a plant is heavily infected, but the disease can be managed and prevented. Our approach combines preventive fungicide applications during the periods of high disease pressure (warm, humid weather), strict sanitation protocols — clean tools, no work on wet foliage, removal and disposal of infected debris — and selective replacement of severely infected plants with more resistant cultivars where appropriate. We also reference the Oregon State boxwood blight risk model, which forecasts daily fungal activity and helps us time applications and pruning to lower-risk days.

If you've recently brought in new boxwoods, holiday greens, or wreaths containing boxwood, those are the most common ways the pathogen arrives on a property. A check of established plantings after that kind of introduction is worth doing.

Volutella Blight

Volutella blight (Pseudonectria buxi) is the most common fungal disease of boxwoods and is often mistaken for boxwood blight. The fungus infects plants that are already stressed — by winter injury, drought, pruning wounds, or heavy leafminer damage — and causes shoots and branches to die back. Leaves turn red, then bronze, then straw-colored, and stay attached to the dead twigs rather than dropping. In humid weather, you can see distinctive salmon-pink or coral spore masses on the underside of affected leaves and stems. That salmon color is the clearest way to tell Volutella apart from boxwood blight.

Treatment starts with reducing the stress that opens the door for the disease: pruning out dead and dying wood (only when foliage is dry, with tools sanitized between cuts), improving air circulation, correcting drainage and watering issues, and addressing winter exposure. Preventive copper-based or other labeled fungicide applications, particularly in spring and fall and after any significant pruning, give the plants meaningful protection. Plants that have lost more than a third of their canopy may be better candidates for replacement than for continued treatment.

Why Diagnosis Matters First

Boxwood symptoms overlap. Browning foliage can be box tree moth, leafminer, boxwood blight, Volutella, winter desiccation, root rot, or simple decline from age and site stress — and on the same property, you can have two or three of these going at once. The right treatment depends on the right diagnosis, and the wrong treatment wastes money and sometimes makes things worse. For example, shearing a planting that has boxwood blight will spread the spores all over the rest of the hedge.

Our ISA-trained arborists will do an on-site evaluation, identify what's actually present, and build a program that fits the scale of your planting and the condition it's in. For some properties that's a single targeted treatment. For boxwood-heavy landscapes — formal hedges, allées, foundation plantings around a high-value home — it's an ongoing monitoring and protection program built around the local disease and pest pressure.

Call us to schedule a boxwood evaluation, or ask about adding boxwood protection to an existing Plant Health Care agreement.