Big Bud Mite on Hazelnut: What Is It and Can You Fix It?

Looking at your hazelnut in winter and noticing some buds that are swollen, round, and much larger than normal? This is almost certainly big bud mite (Phytoptus avellanae), a tiny eriophyid mite that infests hazelnut buds. Unlike the big bud mite that attacks blackcurrant, the hazelnut version is host-specific and does not move to other plants in your garden.

How to Identify Big Bud Mite

Normal hazelnut buds in winter are oval, relatively slim, and pointed at the tip. A bud infested by big bud mite becomes noticeably rounded and swollen — sometimes twice the diameter of a normal bud — and may look slightly bluish or glaucous. When you open an affected bud carefully, thousands of microscopic cream-coloured mites can be seen moving inside. In spring, affected buds either fail to open or produce distorted, stunted growth rather than normal shoots. Infested buds that carry female flowers produce no nuts.

How the Mite Spreads

The mites complete their entire life cycle within a single bud, feeding and breeding through winter and spring. When the bud finally opens or desiccates, the mites migrate to new buds on the same plant or are blown by wind to neighbouring plants. Spread is most rapid in spring during bud burst. Introducing an infested plant from a nursery is the most common route by which big bud mite enters a new garden. Buying from reputable nurseries that inspect their stock reduces this risk considerably.

Management Options

There is no effective chemical control available to amateur growers for hazelnut big bud mite in most countries. Management relies on early identification and physical removal. In winter, when the characteristic swollen buds are easy to spot against the bare branches, prune out and destroy every affected bud or shoot. Do this on a calm, dry day to minimise mite dispersal. If the infestation is severe and widespread across the whole plant, cutting the affected hazelnut back to near ground level (coppicing) removes the majority of the mite population. The resulting regrowth from below ground level is typically mite-free.

After Coppicing

Coppicing a heavily infested hazelnut is a drastic but often necessary intervention. The plant will regrow vigorously from the base and should produce clean, mite-free shoots. Monitor the new growth carefully over the following two or three years for any returning infestation. Avoid bringing in new plants from unknown sources during the recovery period.

Long-Term Tolerance

In gardens where big bud mite is endemic — often near older hedgerow hazelnuts — a low background level of infestation may be unavoidable. Annual winter monitoring and removal of affected buds before bud burst usually keeps the population below a level that significantly reduces the crop. A well-grown, vigorous plant tolerates a modest mite burden without major impact on yield.