Apple proliferation: 'scopazzi del melo'

What it is

Apple proliferation is caused by the phytoplasma 'Candidatus Phytoplasma mali', a wall-less bacterium living in the phloem. It infects apple (Malus domestica) and is known in Italian as 'scopazzi del melo'.

It is one of the most damaging apple phytoplasmoses in Europe, particularly concentrated in northern Italy (Trentino-Alto Adige, the Val di Non).

Vectors and spread

The disease spreads in three ways:

• Insect vectors: the psyllids Cacopsylla picta and Cacopsylla melanoneura, which acquire and transmit the phytoplasma while feeding.
• Root anastomosis: natural contact between the roots of neighbouring plants (including residual roots in the soil).
• Infected propagation material and grafts.

It is not transmitted by pruning tools. C. melanoneura is the main vector in the north-west, C. picta more relevant in the north-east.

How to recognise it

A reliable diagnosis requires at least two symptoms occurring together:

• Witches' broom: a rosette-like proliferation of thin shoots at the branch tips.
• Enlarged stipules and smaller, narrow, finely-serrated leaves with short petioles.
• Early autumn leaf reddening, papery texture, premature defoliation.
• Undersized, poorly coloured, low-sugar fruit — commercially unsaleable.

Why it is an emergency

Apple proliferation is classified as a regulated non-quarantine pest (RNQP) under Reg. (EU) 2019/2072 and is on the EPPO A2 list. In the Autonomous Province of Trento it is subject to mandatory control.

The economic impact is significant: the reduction in fruit size and quality makes the harvest unsaleable, with direct losses for growers.

How widespread it is — and the cost

Apple proliferation is concentrated in the Alpine fruit-growing belt, above all in Trentino-Alto Adige and the Val di Non, the heart of Italian apple production. Provincial monitoring in Trentino recorded an average of 1.54% of plants affected in 2022, on a rising trend, with peaks above 2% in some areas.

On the produce the damage is clear:

• Fruit up to about 50% smaller and lighter, low in sugar and lacking aroma.
• Downgraded or unsaleable harvest, with direct losses for the business.
• Above 1% incidence, intensive grubbing is recommended to reduce the inoculum present in the orchard.

Containment

Measures aim to eliminate inoculum and control the vectors, and are the more effective the earlier and the more area-wide and coordinated they are:

• Grubbing of symptomatic trees with their full root system; full grubbing for abandoned orchards or where over 20% of trees are symptomatic.
• Removal of residual roots left in the soil, which can transmit the phytoplasma by contact between neighbouring plants.
• Compulsory treatments against the psyllid vectors during their activity periods.
• Monitoring and self-monitoring, with coordinated area-wide action: its effectiveness depends on every grower in the area taking part.

In Trentino the matter is governed by provincial decree: failure to comply can lead to fines, grubbing carried out at the owner's expense, and suspension of subsidies.