Beech Bark Disease

Neonectria faginata (with beech scale Cryptococcus fagisuga)

Fungalalso: BBD, Beech scale disease

A slow, disfiguring, and often fatal disease of beech that takes two organisms acting in sequence: a tiny sap-sucking scale insect first weakens the bark, then a Neonectria fungus invades the feeding wounds and kills patches of bark. Affected trees develop oozing cankers, decline over years, and can snap off in wind.

🔎 How to spot it

Look first for the beech scale, which appears as a white woolly or cottony coating on the trunk and large branches, made by soft round yellow insects underneath. Where the fungus has invaded, the bark shows weeping reddish brown spots, sunken or roughened cankers, and in fall tiny bright red lemon-shaped fruiting bodies (perithecia) clustered on the bark. Heavily cankered bark becomes cracked and deformed.

🥀 Damage it causes

The scale feeding opens the bark to infection, and the fungus then kills areas of bark and cambium. As cankers expand and girdle the trunk, the crown thins and branches die. Severely weakened trunks can break in the wind even before the tree is fully dead, a failure known as beech snap.

🔬 What causes it

The disease requires the non-native beech scale (Cryptococcus fagisuga) plus one of two Neonectria fungi, the introduced Neonectria faginata or the native Neonectria ditissima. The scale, brought into North America through Nova Scotia in the late 1800s, feeds on the bark and creates the wounds the fungus needs to enter. American beech (Fagus grandifolia) and European beech (Fagus sylvatica) are both susceptible. There is one scale generation a year, with mobile crawlers spreading in mid to late summer.

🛡️ Prevent it

Keep beech trees healthy and avoid wounding the bark. For a few high-value landscape trees, scout the trunk for the first white woolly scale and treat the scale before the fungus establishes, since scale is the practical leverage point. Do not move firewood or beech logs that may carry scale, and consider that some individual beech trees show natural resistance and are worth keeping.

🧯 If it is already here

On valuable landscape trees, insecticides aimed at the crawler stage in summer, before the insects form their protective wax, give the best scale control, and light scale can sometimes be washed or scrubbed off small trees. Fungicide options against the Neonectria fungi are limited and mainly used by professionals on high-value trees. There is no practical cure for forest-scale infection.

💡 Good to know

The disease spreads as a front across a region: an advancing front where scale arrives first, a killing front where scale and fungus together cause heavy mortality, and an aftermath forest of surviving, often deformed trees and dense root sprouts. Bright red fungal fruiting bodies in fall are the clearest confirmation that the fungus, not just scale, is present.

🌱 Plants it affects

52 plants in the library can be affected by this problem

For educational and informational purposes only. Disease management advice is general guidance drawn from university cooperative extension sources; always identify a problem positively and read and follow the label on any product before use, especially around food crops, children, and pets.