Beech bark disease

What is beech bark disease?

Beech bark disease is a two-part problem. First, the beech scale, a tiny sap-feeding insect from Europe, settles on the bark and feeds. Its feeding makes small wounds. Then fungi in the genus Neonectria get into those wounds, kill patches of inner bark and form cankers.

As cankers grow and join, the tree is slowly girdled. The crown thins and yellows, branches die, and the tree may die. Wood-rotting fungi often move in after the bark dies, and infected trees handle drought and winter cold poorly.

Forest experts describe three stages. In the advancing front, scale spreads into new areas. In the killing front, scale and fungus kill many beech. In the aftermath forest, the disease stays, and thickets of small beech trees can crowd out other species.

Symptoms and signs

• White, woolly specks or flecks on the trunk and large branches (beech scale colonies)
• Tiny red to salmon fruiting bodies of the fungus, often in clusters on the bark
• Red-brown liquid oozing from cankers on the bark
• Round to oval cankers of dead bark
• Sparse, yellowing leaves above dead bark, and branch dieback

Beech bark disease identification: what to look for

• Signs: White, waxy wool covering beech scale colonies on the trunk and main branches. Under the wax, the young scales are tiny, yellow and soft-bodied.
• Signs: Clusters of tiny red to salmon fruiting bodies of the Neonectria fungus on cankered bark. UMass notes that in later stages they may no longer be visible.
• Damage: Round to oval cankers of dead bark (Penn State) that may ooze red-brown liquid.
• Symptoms: Sparse, yellowing leaves on branches above killed bark, and dieback that can become long-lasting.
• Timing: Penn State notes white woolly specks seen on beech bark in August are beech scale.

Disease cycle

Young beech scales settle on the bark, push their mouthparts in and suck sap. They molt twice and become adult females in spring. In midsummer the females lay eggs without mating, then die. Eggs hatch from late summer to early winter. The crawlers move to other parts of the tree or are carried by wind and wildlife to nearby beech. Fungus spores then get into the feeding wounds. UMass says many canker fungi are most active in early spring before trees break dormancy and make spores in autumn.

When to look: Check beech trunks in late summer and fall. Penn State notes the white scale specks in August, and crawlers are about from late summer to early winter. Look for red fungus fruiting bodies and cankers as well.

Beech bark disease look-alikes

A few things get mixed up with it:

• Beech blight aphid: Feeds on twigs and small branches of beech and can be confused with beech scale (Michigan State). Beech scale sits on the trunk and large branches.
• Beech leaf disease (Litylenchus crenatae subsp. mccannii): Causes dark bands between leaf veins and crown thinning, with no white wool on the bark.

How to manage beech bark disease

Cultural control

• On high-value yard trees, check the trunk each year for early scale.
• Michigan State suggests brushing scale off the lower trunk with a soft brush or washing it off with water from a high-pressure nozzle.
• Reduce other stress: keep a large mulch or wood chip ring around the tree so turf roots do not compete, and prune out dead branches (UMass).
• Do not move beech logs or firewood from infested stands to clean areas, especially from late summer to early winter, when crawlers are active (Michigan State).
• Keep and protect beech trees that stay clean. Some trees resist the disease, and Maine Forest Service says they should be preserved.
• In forests there is no practical control, per Maine Forest Service and UMD Extension.

Chemical control

Penn State says there is no control of the fungus itself, so treatment mainly targets the scale. UMD says ornamental beech can be sprayed to stop the scale and to consult an arborist. UMass Extension lists systemic insecticides such as dinotefuran applied to the lower trunk or as a soil drench, horticultural oil on the trunk, and phosphite lower-trunk or soil treatments in spring and fall aimed at the fungus. Michigan State says to apply horticultural oil only while the tree is dormant. Use only products labeled for this use; the label is the law. Work on large trees should be done by an ISA Certified Arborist with a pesticide applicator license (see pesticide applicator license guide).

Use only products labeled for this disease and this site; the label is the law. For trees, work with an ISA Certified Arborist. If you hire someone to apply pesticides, make sure they hold your state’s pesticide applicator license; the rules for each state are in our pesticide applicator license guide.

Prevention

• Watch healthy beech trees each year so scale is caught early.
• Do not move beech firewood or logs out of infested areas.
• Keep a mulch ring around landscape beech and limit other stresses on the tree (UMass).

When to call a pro

Call an ISA Certified Arborist if a valuable beech has white scale on the trunk, red fungus dots, or a thinning crown. An arborist can judge whether scale control is worth it and check large declining beech for rot.

Related guides: Tree database: mature size and planting distance · Pennsylvania tree identification · Firewood rules by state · All pests and diseases

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