NAME OF THE ORGANISM: Phytoptus avellanae sensu lato (ERPHAV)

Evaluation continues

Inspection for 'Phytoptus avellanae' is recommended in EPPO Standard PM 4-31 Certification scheme for hazelnut. Any plant found to be infected should be recorded and immediately removed. In the responses to the questionnaire, DE and PL supported deregulation in the EU. DE considered that 'a generally known pest that can be easily controlled by the operator should not be regulated as RNQP. Horizontal regulation in the marketing regulations should ensure that the consignments to be marketed/moved are “practically free from pests”'. DE also considered that plats for planting was not the main pathway. Evaluation continues on the pathway and impact, considering existing measures to control the pest.

Candidate

Phytoptus avellanae is an eriophyid mite, which is monophagous on Corylus spp. (Ellis, 2001-2024). It has also been identified on hybrid hazels (European hazel, Corylus avellana × American hazel, Corylus americana) (Shanovich et al., 2023).
Mites infest floral and vegetative buds of hazels and feed on the epidermal cells, causing the buds to form galls and swell to several times their normal size. Ultimately, this 'big bud' syndrome causes developmental failure and desiccation of the flowers (Castagnoli & Oldfield, 1996; Shanovich et al., 2023).
The formation of 'big buds' can be observed as early as late summer when generations begin to overlap as eggs hatch and the infestation spreads to the outer scales of the buds. The mites continue reproducing and feeding through the winter, cycling through several generations inside the buds, until the following spring where the adults of the last generation begin to lay eggs and produce nymphs that will migrate. Nymphs continually migrate by walking from 'big buds' to axillary newly formed buds on the hazel plant or by dispersing via wind or phoresy to buds on other hazel plants. For perspective, thousands of nymphs migrate from last year’s big buds, yet only several reach and enter newly formed buds (Özman & Toros 1997a, 1997b; Shanovich et al., 2023).
The mite can travel with plant material: Phytoptus avellanae was most likely introduced to North America via imports of cultivars of C. avellana derived from its native range in Europe (Lovett 1919; Ourecky & Slate 1969; AliNiazee 1998; cited in Shanovich et al., 2023).

The morphological characteristics of eriophyids considerably compromise the active search for a new host plant, so that dispersal is generally passive, mainly due to wind transportation or by exploiting other organisms, such as other arthropods or even humans working in the field (de Lillo et al., 2018; Contarini et al., 2022). However, considering that its biology is closely linked to the crop (they can only live and reproduce on hazel buds), plants for planting may act as its main dispersal route in areas without previous presence of its host (e.g. establishment of new plantations).
The Fruit SEWG considered that both, plants for planting and spread by wind, were significant pathways in areas where the pest is present.

Yes

Phytoptus avellanae, with its feeding activity, is responsible of damages to generative and vegetative buds and induces physiological changes, such as a reduced photosynthetic activity, a disruption of normal plant growth processes, deformation, and necrosis of tissues (¨Ozman and Toros, 1997). All these physiologic effects can have a significant impact on the quality and quantity of nut production (Turco et al., 2024).

Phytoptus avellanae infestations are well known in many areas where the hazelnut is cultivated, but, in recent years, outbreaks have been rising to alarming levels, probably due to the gradual increase in temperatures and the expansion of the crop towards areas not particularly suitable for growth (Contarini et al., 2024). In recent years, this mite has become a major pest of hazelnut orchards in Georgia where sometimes the loss caused by them reaches 90% (Abramishvili et al., 2018). Likewise, Contarini et al. (2022) show an overall increase, in recent years, of big bud mite infestation in the monitored hazelnut orchard located in central Italy. This pest exhibits its harmfulness on several cultivars grown in Europe, becoming one of the main pests in hazelnut plantations and causing remarkable commercial losses.

The damage caused by P. avellanae ranged from 18% to 70% of big bud incidence for different varieties and countries (Pesante, 1961; Viggiani, 1973; Viggiani and Bianco, 1973; Krantz, 1979; Maziarz, 1984; Ozman, 1995; Stamenkovic et al., 1997) (see references in Özman-Sullivan and Akça, 2005). In Oregon (USA), bud damage of up to 20% has been observed in susceptible cultivars of C. avellana such that development of cultivars resistant to P. avellanae is now part of the hazel breeding program at Oregon State University (Krantz 1974; Murray & Jepson 2018). Phytoptus avellanae s.s. damages 50% of buds in South Europe and Middle East (de Lillo et al., 2018). An economic threshold has been established at 15-20% of infested buds (Viggiani & Bianco, 1974; cited in Castagnoli & Oldfield, 1996).

In the hazelnut cultivars in the Blacksea Region, Ozman and Toros (1997b) show that the gall form of P. avellanae feeds exclusively on generative buds and causes formation of bigbuds; whereas the vagrant form of P. avellanae does not cause big bud formation, but feeds intensively on both vegetative and generative buds, on catkins and on young fruit clusters which eventually fall. It can therefore be assumed that the vagrant form also has an economic impact on the crop.

Major

No

Candidate

Evidence of its economic impact is available in the literature

Candidate

Cultivar differences in susceptibility, monitoring big buds and discission thresholds (Contarini et al., 2022): Several studies highlighted differences in susceptibility between cultivars commonly grown in Europe (e.g. Barrios et al., 2014; Contarini et al., 2024) and genetic bases of the susceptibility of hazelnut to big bud mite have been explored, but susceptible cultivars are still preferred by hazelnut industry (de Lillo et al., 2018).
Budbreak to shoot elongation: monitoring, pesticide application (Murray & Jepson 2018).
Chemical treatment of moment of migration (Castagnoli & Oldfield, 1996).

To date, the application of sulphur-based products remains a standard strategy for controlling mite outbreaks, either in IPM or organic hazelnut orchards (Contarini et al., 2024). To complement the use of sulphur, it is also recommended to remove big buds in winter, as this largely removes the sources of infestation for the following spring (Özman-Sullivan and Akça, 2005).

Candidate