Plum crop protection: the pests and diseases that decide the crop

Savvas Pastopoulos, Agronomist MSc, Pastopoulos Agronomics, Neos Mylotopos, Pella, Greece

A complete plant-protection guide for plum: every pest and disease that matters, with the numbers that set the timing. The generation dates come from the official Greek pest-warning bulletins issued for Imathia and Pella and are cross-checked against published research. The article covers the 491 authorised product entries by target, the annual programme by growth stage, and what the timing of pruning actually decides.

1. What makes plum a special case

Plum shares almost every pest and disease with the other stone fruits. It differs in four respects, and each of them changes the programme.

First, it has a fruit moth of its own

The plum fruit moth (Grapholita funebrana) has plum and apricot as its major hosts [7]. Unlike the oriental fruit moth, it never attacks shoots: it goes straight into the fruit. That means there is no warning symptom in the foliage, by the time the damage shows, the larva is already inside the fruit.

Second, it is the definitive host of silver leaf

Chondrostereum purpureum attacks many woody species, but principally plum and cherry [5]. A highly susceptible host, combined with a pathogen that enters exclusively through wounds, in a crop that is pruned every year, is the reason pruning gets a section of its own.

Third, "plum" is two crops

The distinction has practical consequences. An orchard of Japanese cultivars needs more serious attention to planting material and to bacterial spot than one of European cultivars.

Fourth, the warning bulletins measure it

The Regional Plant Protection Centre of Thessaloniki issues bulletins dedicated to plum, driven by a phenological model fed from weather stations in Imathia and Pella [9]. That is not a given: the Volos and Kavala centres cover plum inside combined "stone fruit" bulletins with no date model, and the Achaia centre issues no stone fruit bulletins at all [9]. For Central Macedonia, then, a ready-made timing tool exists and it is free.

Sources: 2 3 4 5 7 8 9

2. The ranking: what actually costs money

A plant-protection programme without a ranking turns into a spray calendar. The ranking below comes from three criteria combined: how often the problem occurs in Central Macedonia, how directly it hits marketable fruit, and how hard it is to correct once established.

3. The generation calendar, with Greek dates

This is the section that makes the difference, because the dates are not translated from foreign handbooks. They come from the Thessaloniki centre's bulletins, based on pheromone trap counts in Imathia and Pella [9].

Plum fruit moth, the complete Greek model

Thessaloniki centre plum bulletins, 2026: number 19 of 22 April, 31 of 25 May, 38 of 17 June and 47 of 17 July [9]. The dates shift every year with the weather and are not to be copied as a calendar, they hold as an order of magnitude and a sequence of events. The actual bulletin for the current season is free and appears in the same week.

San Jose scale, three generations, and three independent Greek studies

Here the documentation is unusually good, because the insect was studied systematically in northern Greece.

How much the scale's pheromone trap is worth, a Greek finding

In apple orchards of the Florina region, no relationship was found between the male population caught in the traps and the larval population, a result the researchers described as the most important of the work for monitoring purposes [17].

In practice, the pheromone trap gives timing, not density. It is used to set the biofix, and confirmation of crawler emergence is made with black sticky tape wrapped around the scaffold limbs.

The degree-day model, and why the base temperatures are not mixed

The two sets of values are not contradictory: 300 to 400 degree-days refer to the start of emergence, 600 to 700 to peak movement [19]. The base temperatures, however, really do differ and are not interchangeable. For European conditions, the model of 400 degree-days above 7.3 °C is the one to use [18].

Peach twig borer and oriental fruit moth, a Greek degree-day model

For these two insects there is a published model from Pella, with four years of measurements [20]:

Peach twig borer and the leafroller are rarer in Greece than their place in the literature suggests, and rarer than the plum fruit moth and Grapholita molesta. The model was developed in peach orchards of Pella [20]. Transferring it to plum is reasonable for the same insect species, but it has not been validated there. For the plum fruit moth there is no verified complete degree-day model with a base temperature, a biofix and degree-day sums per generation, which is why the Greek bulletins work with the trap and the phenological stage, not with heat accumulation.

Are there degree-days for the plum fruit moth?

It is the first question asked by anyone used to working with heat sums on peach. The answer is no: there is no verified, complete degree-day model for Grapholita funebrana with a base threshold, a biofix and degree-day sums per generation. The only published values retrieved are that egg laying begins in May once the temperature reaches at least 14 °C, and that the optima are 24 to 26 °C for egg laying and 18 to 22 °C for trap catches [10]. These are behavioural thresholds, not developmental ones, and they cannot be summed.

In place of a heat sum, the method for plum is the trap plus the phenological stage. That is exactly what the Greek bulletins do, and it is why the calendar in this section is expressed in dates rather than in degree-days [9]. The interval has been measured here: in the Thessaloniki bulletins, 4 to 6 days elapse between flight and egg laying and 4 to 5 days between egg laying and hatching [9]. Once catches peak, the window for treating the eggs opens within a few days.

The "about 10 days" of incubation from the foreign source [10] does not agree with the 4 to 5 days of the Greek bulletins [9]. The likeliest explanation is temperature, the foreign figure refers to a cooler Central European May. The two values are not merged and are given separately. For Greek conditions the Greek one applies.

Sources: 8 9 10 11 12 13 14 15 16 17 18 19 20

4. The pests

The order that follows is neither alphabetical nor taxonomic. It is the order in which these pests cost a Greek plum orchard money, and within each species precedence goes to whatever determines the timing of the intervention, not to whatever describes the insect.

4.1 Plum fruit moth, Grapholita funebrana

This is the pest that defines the crop. Plum and apricot are the main hosts of the species according to EPPO [7], and the larva goes straight into the fruit: there is no shoot attack that could serve as an early warning.

The damage is described in the same way by four independent sources [10] [24] [25] [9]: a tunnel through the flesh towards the stone, a cavity filled with brown frass, gummosis at the entry hole, premature colouring of the fruit from green to purple, and premature fruit drop. The Greek bulletin adds that the larva, once it has completed development, exits to pupate in protected positions on the trunk or in the soil [9], and there it overwinters as a larva in a cocoon, in bark crevices, at the base of the tree or in the ground [10].

Monitoring with the pheromone trap

Monitoring is weekly, from petal fall to harvest [24]. The decision to intervene comes from catches together with the phenological stage, which is how the Greek bulletins work [9].

For trap density there is only one recommendation [25]: one trap per 2 hectares in large uniform blocks, two traps per hectare in small or irregular ones, of the Delta type for sensitivity, with the lure replaced every 4 to 6 weeks.

Mating disruption: it works, but not everywhere the same

This is one of the few areas of plum crop protection where two independent Italian studies on plum exist, rather than a transfer from peach.

The two studies agree that the method works and disagree on the economic outcome. The likeliest explanation is initial population pressure, the isolation of the block and the susceptibility of the variety. Two details determine success:

• The dispensers go up before the first flight, in early April, and are placed on the edges of the block, not in the centre [26].
• Optimal emission lasts about 60 days and drops by 66% after 72 days in the field [8]. With three generations, a single placement is not enough.
• The method requires a large and isolated area; the literature notes that some applications succeeded and others did not, and that isolation from wooded land is a precondition [10].

Both Italian studies used dispensers commercially intended for G. molesta: the active pheromone, (Z)-8-dodecenyl acetate, is shared by both species [8] [26].

4.2 San Jose scale, Diaspidiotus perniciosus

The calendar of the three generations and the Greek studies that support it were given in section 3. What follows here concerns the damage and the intervention.

On the fruit the symptom is pathognomonic and five independent sources describe it in the same words [16] [23] [21]: around each individual a purple or reddish halo forms, within 24 hours of the crawler settling [16]. When the scale cover is removed, a pale spot like a target remains [23]. The fruit does not rot; it is commercially downgraded, and that is enough.

On the wood the damage is more serious and slower: splitting of the bark, gummosis from the scaffold limbs, rough bark, dieback of branches and, if neglected, death of the tree [23] [21].

The winter spray, three countries agree

The insect overwinters predominantly as a first-instar nymph, the so-called black scale stage, and a few as gravid females, this is confirmed by EPPO [16], by Katsoyannos and Argyriou for Greece [11] and by two American agencies [23]. That stage is the only one the oil can reach in time.

The Greek bulletin notes explicitly that the same oil also covers other overwintering forms of phytophagous insects as well as mites [22]. In practice, the same spray catches San Jose scale, white peach scale, the globose plum scale and the eggs of the European red mite. It is the most cost-effective intervention of the year.

The beneficials: where the choice of active substance has consequences

In Northern Greece San Jose scale has established natural enemies, and this is documented Greek data, not a generic recommendation:

• Encarsia (Prospaltella) perniciosi, was introduced and became established in Greece [52], with four generations per year in Northern Greece [12].
• Cybocephalus fodori, the main predator of the scale in Northern Greece [11].

The study by Navrozidis and co-workers on apricot in Northern Greece shows it clearly: fenoxycarb, buprofezin and especially diofenolan gave successful control with minimal effect on the beneficials, whereas methidathion had a devastating effect on the parasitoid [12]. Methidathion is no longer approved in the European Union, but the lesson stands: a growth regulator and a non-selective organophosphate are not interchangeable, even when they give the same mortality on the scale.

Sources: 11 12 16 21 22 23 52

4.3 Peach twig borer and oriental fruit moth on plum

Both species have plum as a secondary host: EPPO gives apricot and peach as the main hosts of Anarsia lineatella, with plum as a mere host [53]. That, however, is a classification, not an exemption. In central Italy severe damage from peach twig borer was repeatedly observed on plum varieties grown for drying, to a degree that justified combined mating disruption against both species [26].

In Greece, two independent sources agree that the flight of the peach twig borer begins in the last ten days of April [9] [54]. For G. molesta the Greek bulletins report four to five generations [9] [54], against three to four in the Pacific Northwest of America [51], the difference is explained by the warmer climate, and the Greek figures are the ones that apply here.

The Greek degree-day model from Pella [20], cited in section 3, covers both of these species and is the best available timing tool, with the explicit caveat that it was developed on peach.

4.4 Plum sawfly, Hoplocampa flava and H. minuta

This is the pest around which the greatest confusion circulates in Greek, because European texts present it as a primary problem of plum and Greek growers rarely see it.

Its biology is simple, and for that reason the intervention window is narrow. One generation per year [28] [31]. It overwinters as a larva in a cocoon in the soil, pupates in spring, and the adults emerge exactly before the flower opens: "one to two days before the start of flowering" according to one source [31], "shortly before the hosts begin to bloom" according to the second [28], and in Ukrainian measurements 31 to 42 days from the start of bud swell, peaking in early May with a total flight duration of 17 to 34 days [29].

Use of fine white traps

The choice of colour governs the catch. In a comparative trial [29] white sticky traps caught 89 adults per trap against 10 for yellow and blue, and fewer still for red and green. The white traps accounted for 53 to 62% of the total, and up to 80% at the peak. Placement at 1.2 metres above the ground. Hungarian work in three plum orchards with three sawfly species used the same white chromotropic traps, with maximum catches of 146 and 80 individuals [30].

The period of use is equally specific: from about one week before to one week after bloom, with checks several times a week [28]. Outside that window the trap says nothing.

The damage is disproportionate to the population, because each larva destroys five to six fruitlets, two sources agree, with five in one [28] and about six in the other [31]. Eggs are laid in slits at the tip of the calyx or in fruitlets of 4 mm and above, and the larva destroys stone and flesh [28]. Historically, losses of 30 to 80% are recorded in areas of Crimea [31] and a damage range of 36 to 84% [29].

The intervention, when justified, is made immediately after petal fall [28] [31]. The second adds a pre-bloom intervention at the balloon stage, as well as autumn ploughing or disc-harrowing between the rows, because the larvae overwinter in the soil [31]. The cultural measure is the only one that does not depend on a window of days.

4.5 Aphids, and their role in the transmission of sharka

Three species share the plum, and which one is "the main one" depends on the criterion. No source ranks them cumulatively, so the ranking is made by type of damage.

The direct damage of all three follows the same pattern: they feed on the shoot tips, causing stunting and deformation in young trees, while in mature trees they reduce the following season's fruit set; the honeydew leads to sooty mould on the fruit [33]. For H. pruni specifically, leaf curling appears only when very young leaves are attacked [32].

The timing of monitoring is everything: inspection of the shoots begins before bud burst, and management is effective before the leaves begin to curl [33]. Once curling has occurred, the leaf shields the colony from the spray liquid. No source gives a numerical threshold for aphids on plum.

Vectors of sharka

A Romanian study on seven plum varieties ranked the vectors [34]: Phorodon humuli was the most efficient, with 80% infected trees in susceptible varieties and 100% in all three years in the variety Vanat romanesc. Next come Myzus persicae and Hyalopterus pruni with up to 80%, and variable efficiency for Brachycaudus cardui and B. helichrysi. The range was 20 to 60% in less susceptible varieties and 40 to 80% in highly susceptible ones.

There is disagreement over H. pruni: the study above ranks it as an efficient vector at up to 80% [34], whereas the general literature describes it as a poor vector of sharka [32]. The disagreement has not been resolved. A possible explanation: the study measured under mass-inoculation conditions, whereas the general assessment concerns the relative epidemiological contribution in the field. Both versions are reported here, with no preference given to either.

4.6 The other scale insects

Sphaerolecanium prunastri, the globose plum scale

Its name is not accidental: it shows a strong preference for Prunus, and especially for Prunus domestica [35]. British texts describe it as "a southern European pest of plum and peach". Greece is not explicitly named in the distribution, but it lies within the Mediterranean zone described.

• One generation per year, overwintering as a second-instar nymph [35].
• Adults in late April and early May in central Europe; egg hatch in late June.
• Damage: stunting, dieback of shoots, death of the tree, and abundant sticky honeydew leading to sooty mould.

Pseudaulacaspis pentagona, white peach scale

Here Greece is explicitly named in the European distribution [36], and the species is referred to as "white scale or white peach scale" in the Greek stone fruit bulletin, with a recommendation for winter mineral oil up to bud swell [22].

Generations are one to four depending on the climate [36], for Greece two to three are expected, although there is no Greek measurement. The hosts exceed 100 genera, with Prunus and especially peach prominent among them. The damage extends to dieback and death of twigs, scaffold limbs, even large trees. The summer spray, when needed, is made while the crawlers are active, they are recognised as dust on the sticky band around the trunk [36].

For Parthenolecanium corni, the European fruit lecanium, it was not possible to retrieve verifiable data on generations, overwintering and crawler timing from a reliable source. The species appears in the Greek list of approved products for plum as Lecanium prunastri, but its biological data are not presented here because they could not be verified.

4.7 Spider mites and eriophyid mites

The European red mite (Panonychus ulmi) overwinters as an egg on the spurs and in summer produces many overlapping generations [37]. The damage begins as stippling and bronzing of the leaves and ends in reduced vigour and reduced fruit size.

The only numerical threshold documented for spider mites on plum is a dormant spray when 20% or more of the fruiting spurs carry eggs [37], and it comes from the same sampling of 100 spurs carried out for San Jose scale. Two decisions from one job.

For summer interventions and for the two-spotted spider mite (Tetranychus urticae) there is no published threshold specific to plum. The decision is based on the appearance of damage and on the ratio of predatory mites. The source of the winter threshold itself recommends a summer intervention only when the population begins to cause damage to the foliage [37].

The two eriophyid mites that really concern plum

Acalitus phloeocoptes, the plum bud gall mite, is confined almost exclusively to the genera Prunus and Cotoneaster, with damage on almond, apricot and plum [38]. The mites move beneath the bud scales and their feeding causes gall formation on buds and twigs. They overwinter inside the galls; in spring the galls split open and the adult females disperse. It has multiple generations per year and each female produces 700 to 850 eggs. Control combines winter removal of the infested twigs with a spray timed to the spring emergence [38], that is, pruning is here part of crop protection, not only of tree training.

Aculus fockeui causes mature leaves to curl upwards, with the lower surface brown or bronzed and rough, and yellow spots on young leaves that end in shot-holing [39]. It overwinters as an adult female beneath the bud scales, with a generation of 6 to 22 days and continuous production of generations through the summer. Monitoring requires a hand lens of at least 20x. The source itself states frankly that the effect on vigour and yield is uncertain, and that its importance is greater in nurseries and young trees. There is no numerical threshold.

4.8 The wood borers

Capnodis tenebrionis, the most important in the Mediterranean

The 2024 review in the Journal of Integrated Pest Management [40] explicitly names plum among the hosts and is the best available source for the species. The findings that change practice:

• The larva kills, the adult merely annoys. The larvae tunnel in the roots and in the lower part of the trunk; "a few larvae can kill a large tree within two years". The adults feed on shoots and buds and are tolerated by large trees, but are devastating in nurseries and young plantings.
• The cycle is not annual. The adults live more than a year and may overwinter twice; larval development lasts 6 to 18 months in the field. This means that the population is not wiped out by one good year.
• Egg-laying is a matter of temperature. It begins when the temperature reaches 23 °C and may continue until September, but most eggs are laid in the optimal range of 30 to 34 °C, that is, usually in July or August.

There are no economic thresholds, and the review itself states that monitoring devices and semiochemical control are lacking [40]. 3-methyl-1-butanol has shown attractiveness to both sexes. Among the biological agents, entomopathogenic nematodes gave mortality above 90% under laboratory conditions with 50 infective juveniles per insect, and 75 to 90% control in the field with Steinernema carpocapsae at a rate of 1 to 1.5 million infective juveniles per tree, together with a 1.25% chitosan formulation [40]. The timing of chemical interventions against the adults is April and May for the adults of the previous year and August to October for those of the current year.

Leopard moth and shothole borer

The leopard moth (Zeuzera pyrina) has a two-year cycle from egg to adult [41] and bores tunnels of about 20 centimetres inside branches. The same source notes that it has no tendency to outbreaks and appears rather sporadically, with a preference for more southerly and warmer sites. Plum is not named in the host list of that source.

The shothole borer (Scolytus rugulosus) attacks apple, pear, cherry and plum [42]. It is primarily a problem of injured or stressed plants, but, and this is the critical message, healthy trees next to abandoned orchards or piles of infested wood do get attacked. The damage is perforation of the vascular tissues with wilting and dieback of branches, and the many small round exit holes of about 2 mm give the branch the appearance of buckshot damage. Two generations per year, overwintering as a larva inside the tunnels, second generation from August onwards. Inspection is carried out in late spring, looking for holes that ooze sap and sawdust. The same source is categorical: the best tool is to keep the trees healthy with correct pruning, adequate water and fertilisation [42].

4.9 The fruit flies

Ceratitis capitata, Mediterranean fruit fly

Plum is a recorded host, and two independent official sources agree: EPPO explicitly lists Prunus domestica and Prunus salicina in the host list [45], and the official host list of the American agency APHIS includes both species [46]. The insect is established in mainland Greece and in Crete [45].

No quantitative susceptibility data for plum were found, pupae per kilogram or a reproductive index on the host. Neither of the two sources gives a severity rating. In practice, plum is a secondary host relative to peach, fig and citrus, and the risk concerns mainly late varieties in areas of high pressure, adjacent to peach or fig trees. This is an assessment based on geography, not a measured quantity.

Drosophila suzukii, yes, but not among the most susceptible

EPPO classifies stone fruits as particularly susceptible and lists Prunus domestica among the hosts [43]. The species is established in mainland Greece and in Crete. It produces 3 to 9 generations per year. The biology of egg-laying defines what is dangerous: it prefers slightly unripe, intact fruit, and the fruit becomes susceptible as soon as it begins to colour; it prefers varieties with red colour, late harvest and a less firm skin [43].

The only quantitative evidence of relative susceptibility identified is indirect: Japanese work citing an American study found that 7% of eggs were laid on plums against 73% on cherries [44]. It is a secondary citation and an old one; the study itself ranked strawberry, raspberry, blackberry, cherry and blueberry as the most susceptible and did not test plum.

Monitoring is carried out with apple cider vinegar traps, for their effectiveness and convenience [43]. The conclusion for the grower: a confirmed but secondary host, with the risk concentrated in late, dark-coloured, soft-fleshed varieties and in proximity to cherries or soft fruit.

4.10 Cacopsylla pruni, the phytoplasma vector

It causes no damage by its feeding. It matters only as a vector of European stone fruit yellows phytoplasma, and its biology defines an extremely specific window.

Two independent sources agree on every point [47] [48]:

• Univoltine, one generation per year.
• The remigrant adults, that is, those that have overwintered, are found on Prunus from February to May. The new generation from May to June. After July the insect is absent from Prunus.
• In summer and winter it migrates to conifers in mountain areas.
• Transmission requires a latent period of eight months; this is why the dangerous individuals are the early-spring remigrants, not the new generation [47].
• The preferred host and inoculum reservoir is blackthorn (Prunus spinosa) [48].

In Greece the disease is described as widely distributed, with documented presence in Macedonia, Thessaly and the Peloponnese [47]. A notable geographical limit: no report of the disease from Crete, nor from southern Spain, Sicily, Apulia, Cyprus and Malta, the authors attribute this to the absence of the preferred wild Prunus, especially blackthorn, and to conditions unsuitable for the survival of the vector [47].

4.11 Halyomorpha halys, the brown marmorated stink bug

It is established in Northern Greece. The first record was made on peach and olive trees in the prefecture of Imathia, with samplings in July and August of 2018 and 2019 and significant levels of fruit damage, especially in 2018 [49]. Overwintering adults were recorded systematically in shelters and structures near the orchards, and that is also where the population is located in winter.

The measure of the potential risk comes from Italy [50]: up to 60% infested fruit under integrated management and above 90% under organic management, with the 2019 outbreak reaching 80 to 100% crop losses. There the insect produces two full, partly overlapping generations per year. Monitoring with aggregation pheromone traps gives an indication of presence, not of density. The most effective measure is exclusion netting; an integrated management approach with targeted interventions on the margins achieved a 40 to 50% reduction in insecticides.

4.12 Two more that deserve a line

Leafrollers, Adoxophyes orana is included in the Greek degree-day model from Pella [20], with a threshold of 7.2 °C, and it is the second most frequent insect target among approved products for plum. It was studied on peach.

Bud weevil, it is reported in an official Greek stone fruit bulletin as a pest of secondary importance, active particularly in November; the adults feed and lay eggs in the buds, and a spray is recommended only where a high population is found [9].

Sources: 7 8 9 10 11 12 16 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54

5. Pruning, and why its timing is a plant-protection measure

In no other stone fruit does the timing of pruning weigh as heavily as it does in plum. The reason is that two of its most serious pathogens enter exclusively or mainly through wounds. What is critical, however, is not the month as such, it is the moisture at the moment of the cut and in the days that follow, the size of the cut, and the history of the block.

Silver leaf, a fungus that gets in no other way

Chondrostereum purpureum has a wide range of woody hosts, but the best available source, specific to plum, describes it as a problem mainly of plum and cherry, more frequent in older trees [5]. Entry takes place mainly through pruning wounds and other fresh wounds in living or recently dead woody tissues.

Spore production is at its maximum in autumn and winter, and wounds made at that time take longer to heal [5]. The penalty is twofold, and this is why the recommendation is categorical: prune in late spring and early summer.

The remaining measures follow from the same reasoning [5]: burning the infected wood; timely removal of dead branches, especially as soon as the fruiting bodies with the characteristic purple lower surface develop, as these are the source of the spores; disinfection of tools between cuts; sealing of large cuts.

No duration of wound susceptibility in days or weeks is stated here. The source does not give one and it could not be verified elsewhere. Figures in circulation for "X days of susceptibility" have no documentation for this fungus.

Bacterial canker, the same recommendation by another route

Bacterial canker is caused by Pseudomonas syringae, and the picture of the pathovars is not clear-cut. Both attack plum. P. syringae pv. syringae has a wider host range and is described as the more infectious one for stone fruits generally [6]. pv. morsprunorum race 1 includes plum-specialised strains: isolates from plum were pathogenic on plum but non-pathogenic on cherry, while isolates from cherry showed reduced pathogenicity on plum [55]. Race 2 and pv. syringae were pathogenic on both.

The study does not state which pathovar predominates in the field, and which one will be found in any given orchard is not predictable from the literature. The variety matters a great deal: Victoria proved susceptible to pv. morsprunorum race 1, whereas Marjorie's Seedling was not susceptible to any strain inoculated through the leaf scars [55].

How it enters the tissues

Two sources agree that the main route is the leaf scars during autumn leaf fall, followed by pruning wounds, other mechanical injuries and the crotches of the scaffold limbs [6]; the second used inoculation at the leaf scars precisely as a standard field test, confirming it as the accepted natural point of entry [55]. Tissues weakened by frost are attacked.

The cycle explains why: the bacterium overwinters inside the cankers and in the buds, in spring it becomes epiphytic on the leaves and plant surfaces, and at leaf fall it passes from those surfaces into the buds, mainly through the scars [6].

The symptoms are cankers, gummosis with orange-brown sticky gum oozing from shallow depressions, necrosis of bark and trunk, spots on the fruit with a sunken dark centre, and water-soaked leaf spots [6]. The latent period is the dangerous part: visible symptoms may appear as much as 18 months after the initial infection [6]. In practice, the canker seen this year was written last year.

What holds for both wound diseases, whichever month is chosen for pruning: cut in dry weather and with a dry forecast, not merely without rain at the moment of the cut, disinfect tools between trees, and remove the cut wood from the orchard [5] [6]. The large cuts, removing a scaffold limb, reworking an old tree, are slow to heal and are the real point of entry; if anything is to be moved to late spring, it is those.

Sources: 1 5 6 38 42 55

6. The diseases

The order again follows cost, not taxonomy. Two wound diseases, silver leaf and bacterial canker, were covered in section 5, because managing them is a pruning decision and not a spraying decision.

6.1 Monilinia, brown rot

It is the most damaging fungal disease of stone fruit in the Mediterranean, and in the Greek list of products approved for plum it is the target with more products than any other [75]. It is covered in a separate, complete article that examines all four Monilinia species, the temperatures, the wetness hours, the post-harvest phase and the susceptibility of each crop. Only the points that concern plum specifically are given here.

• Overwintering takes place in infected twigs, in old floral parts and, above all, in mummified fruit on the tree [56]. The mummified fruit left hanging is next spring's inoculum, removing it in winter is the cheapest intervention of the year.
• The fruit susceptibility curve explains why there are two spray windows and not a continuous one: susceptibility is highest from bloom to pit hardening, lower during embryo development, and rises again as the fruit ripens [56].
• Latent infection: early infections remain symptomless until ripening begins [56]. Fruit that rots in the crate was infected in the field.
• Timing of interventions: early popcorn stage, full bloom and petal fall for blossom infection; pre-harvest applications when rainy weather threatens [56].

6.2 Rust, Tranzschelia discolor

The taxonomy comes first, because it causes confusion in Greek and foreign texts alike: Tranzschelia pruni-spinosae var. discolor is the same fungus as T. discolor, not a different pathogen [57].

The importance of the disease for the following year

This is the critical message and it is repeated by two sources that share the same basis [58] [59]: early infections are the most damaging, because they reduce photosynthetic capacity and cause premature leaf fall, which reduces the tree's carbohydrate reserves and lowers the following year's yield. Rust does not spoil this year's fruit. It spoils last year's planning.

The alternate host, and why it does not change practice

The fungus is macrocyclic and heteroecious: stages 0 and I occur on anemone (Anemone coronaria), and stages II, III and IV on Prunus [57]. However, two sources agree that the alternate host is not necessary: the primary inoculum overwinters as mycelium inside infected wood [57], and in Britain only the teliospore and urediniospore stages have been observed [58].

Anemone coronaria is native and abundant in Greece, so the aecial stage is theoretically available here in a way that it is not in Northern Europe. No source, however, documents that this stage occurs on anemone in Greece. It is not stated here as a fact. Agronomically nothing changes: the fungus maintains itself on Prunus on its own.

The intervention, where it is made, is placed in late spring [59], and the cultural measure is pruning that reduces humidity within the canopy. The varieties reported as resistant, Ferbleue, Guinevere, Merton Gage, are British and are not relevant to Greek plantings [59].

6.3 Shot hole, Wilsonomyces carpophilus

The synonyms that will be found in Greek and foreign texts are Stigmina carpophila, Thyrostroma carpophilum and Coryneum beijerinckii. It is the third fungal target in number of approved products on plum [75].

The symptoms are small round spots, brown to purple, usually up to 6 mm, from which the tissue drops out to give the shot hole; on the fruit, spots with a gummy exudate; on the twigs, reddish sunken lesions, and on older wood cankers with a sooty appearance [60].

The figures, and why they are not merged into one

There are two independent data sets, from different hosts, different temperatures and different endpoints. They are presented separately, with attribution, because merging them into a single figure would be an error.

The disease is polycyclic: spores are produced from infected buds and shoot lesions throughout the growing season [60]. It overwinters in infected buds and twigs, and the cankers on older wood are the main source of spores. The two interventions recommended in the American handbook, for peach, are a dormant spray at 50% leaf fall and an application at shuck fall, together with avoidance of sprinkler irrigation [60]. No equivalent recommendation specifically for plum was found.

6.4 Scab, Venturia carpophila

The literature specific to plum is thin. The best available quantitative epidemiology concerns Japanese apricot (Prunus mume) and not plum [62]. The figures are given with that reservation.

The feature that defines management is the exceptionally long latent period: 42 to 77 days. Under field conditions, 55 days elapsed between the first conidial catch on 24 March and the appearance of symptoms on 18 May [62].

• Optimum growth temperature of the pathogen: 20 to 27 °C [62].
• Source of primary inoculum: the two-year-old branches, the lesions that overwintered on them [62]. This is why pruning out the infected branches is a control measure and not mere tidying.
• Conidial dispersal from late March to late April, peaking when temperatures exceeded 20 °C [62]. In practice, one main infection period per year.

The wetness duration required for infection was not found in any source, for any host. No figure is given here.

6.5 Bacterial spot, Xanthomonas arboricola pv. pruni

This disease is the prime case where the answer depends on which plum is involved. Three independent sources agree [2] [3] [63]: the varieties of the Japanese-Chinese group (P. salicina) are generally more susceptible than European plums; yield and quality losses have been observed on peach, nectarine and Japanese plum, whereas minimal damage is expected on cherry and European plum [3].

Leaf symptoms begin as small water-soaked spots and develop into brown to black angular spots with a light green or yellow halo, from which the tissue drops out to give a shot hole [63]. On the fruit, dark spots up to 10 mm, sunken and cracked.

Temperature and wetness, the best quantitative source, with an explicit reservation

The values above come from a model with a very good fit, a correlation coefficient of 0.93 and agreement with the observations in 92% of the validation cases [64]. The authors themselves, however, state explicitly that the study was carried out only on an almond-peach hybrid rootstock, selected as representative of Prunus, and was not carried out on plum. They themselves call for field validation on inoculated plants of different species. These are not presented here as plum figures. The independent qualitative statement of EPPO is compatible: favourable conditions are a warm period with maxima of 25 to 33 °C, light frequent rains, fairly strong winds and heavy dews [2].

Where it overwinters, and one difference that concerns plum specifically

EPPO reports overwintering in dormant buds, leaf scars and cankers [2]. Italian field epidemiology adds that the bacterium is recovered from infected fallen leaves, buds and scars for up to 6 or 7 months after infection, and that in the Po valley the summer cankers on plums act as overwintering sites, whereas in the peach orchards studied no summer cankers were observed at all [65].

The British description completes the same pattern: spring cankers are usually found on the tips of overwintered twigs, and perennial cankers develop on plum and apricot, girdling the wood and causing dieback [63]. This perennial canker behaviour is a real difference between plum and peach and has a practical consequence: on plum the inoculum can be maintained in the same wood for more than one season, so removal of the infected twigs counts for more.

Dispersal occurs by insects, wind and rain, by contaminated equipment and by splashing of droplets from infected leaf scars [63]. The measures are certified planting material, which is also the regulatory requirement, see section 8, tolerant varieties, disinfection of tools and footwear, avoidance of sprinkler irrigation, and copper products with the explicit note that they reduce the load but carry a risk of phytotoxicity [2] [63].

Bacterial spot is present in Greece. The first report was made on almond, but the full bibliographic record could not be retrieved in its entirety and for that reason it is not cited as a numbered source. Furthermore, the British information sheet describes the disease as "notifiable", this applies to Great Britain following its withdrawal from the European Union and does not transfer to Greece [63].

6.6 Wood cankers, Leucostoma and Cytospora

The causal agents are Leucostoma persoonii and Leucostoma cinctum, with the imperfect forms Cytospora leucostoma and Cytospora cincta, and plum is explicitly a main host [66].

The entry points are exactly the same as those of bacterial canker: leaf scars or dead buds during dormancy, pruning wounds and especially cuts made in early dormancy, twigs with winter injury, and narrow-angled branch crotches [66].

The temperatures are useful because they explain why the problem builds up in winter: infection occurs at 14 to 20 °C, but lower temperatures, 2 to 8 °C, permit greater colonisation once infection is established; conidial dispersal is correlated with the hours when the temperature is 10 to 15 °C and relative humidity above 90% [66].

The recommendation is, for the third time in this same article, pruning in late spring [66], together with surgical removal of the cankers, cold-hardy varieties, irrigation management, control of rodents and wood-boring insects, and protection of the cuts.

6.7 The soilborne diseases

Phytophthora, crown and root rot

The threshold condition is simple and measurable: periods of 24 hours or more with saturated soil favour infection [67]. Nothing else is needed for the problem to start.

The message that concerns plum specifically is positive and practical: plum rootstocks are less susceptible than peach rootstocks [67]. This is a real advantage of the Marianna and Myrobalan type rootstocks and the reason they are chosen on heavy or poorly drained Greek soils.

It should not be overestimated. The same source writes that rootstocks differ in susceptibility depending on the Phytophthora species and none is resistant to all pathogenic species [67]. Management remains a matter of site, rootstock and irrigation choice, in particular avoidance of excessive watering in spring and autumn, when soil temperature favours the disease.

Armillaria mellea

Diagnosis rests on two features that together are definitive [68]: white to yellowish fan-shaped mycelial mats between the bark and the wood of infected roots, and dark brown to black rhizomorphs on the root surface.

The fungus survives on dead roots in the soil. The duration of survival is not given by the source and no number of years is reported here. For the rootstocks, the message is measured: all stone fruit rootstocks are susceptible, but some, such as Marianna 2624, are less affected [68]. No comparative data against peach or almond rootstocks are given.

The measures, all from the same source: avoidance of recently cleared land and of sites with a history of the disease; excavating the crown to a depth of 23 to 30 centimetres may slow the progression; a trench 1.2 metres deep with a plastic barrier to interrupt root-to-root contact; pre-plant soil fumigation in late summer or early autumn, with better results where the soil is shallower than 1.5 metres.

Verticillium dahliae

The diagnostic pattern is asymmetry: leaf yellowing, branch wilt, necrosis of fruiting organs and twigs, reddish-brown streaks in the sapwood, and the characteristic "some branches appear healthy while others wilt and die" [69].

The microsclerotia survive in the soil indefinitely according to the source, which gives no number of years [69]. The frequently quoted "10 to 14 years" is not documented by it and is not written here. Management includes pre-plant soil testing, restriction of nitrogen, avoidance of excessive irrigation and of severe pruning, removal of symptomatic branches before leaf fall, and disinfection of tools.

The source concerns cherry and does not deal specifically with the susceptibility of plum. A ranking of plum susceptibility to Verticillium wilt was not verified. Verticillium dahliae is in any case listed as a regulated non-quarantine pest in Annex IV, Part I of Regulation 2019/2072 for many fruit crops, including Prunus [1], that is, the planting material must be free of it.

6.8 Two diseases that are often mentioned and do not concern plum

Eutypa lata. It attacks mainly apricot and grapevine and sporadically cherry; plum is not listed among the hosts [70]. It is mentioned here only so that it is not looked for. Its figures, for anyone who also has apricots: perithecia form where annual rainfall reaches at least 355 millimetres, pruning wounds remain susceptible for more than 6 weeks in cool weather and about 2 weeks in warm weather, and pruning of apricot and cherry is recommended only in July and August in inland areas [70].

Red leaf blotch (Polystigma rubrum). The species is taxonomically confirmed on plum and on blackthorn, but the modern literature and all the recent epidemiological work concern Polystigma amygdalinum on almond, not P. rubrum on plum. On plum it is associated mainly with wild Prunus spinosa and appears to be of secondary commercial importance. No quantitative epidemiology on cultivated plum was found and the almond figures are not transferable.

Sources: 1 2 3 9 5 6 75 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70

7. Viruses, phytoplasmas and planting material

The diseases in this section share one feature that sets them apart from all the previous ones: they are not controlled by spraying. They are controlled by what was planted and by what leaves the orchard. That is why they are grouped together.

7.1 Sharka, Plum pox virus

The official name under current taxonomy is Potyvirus plumpoxi, family Potyviridae, known for decades as Plum pox virus [71].

Ten strains, not four

Ten strains are recognised: D, M, EA, C, Rec, T, W, An, CR and CV [71]. The three with very wide geographical distribution are M, D and Rec, and these are the ones relevant to plum; the C, CR and CV group is adapted to cherry.

Many texts, including widely circulated teaching material, still refer to "four serological strains, M, D, EA and C". This is the older serological classification, which has been superseded by the genetic classification into ten strains [71].

The symptom that identifies sharka on plum

On the leaves, chlorotic spots, bands or rings appear. On the fruit, chlorotic spots and rings, deformation and internal browning of the flesh. The diagnostic feature, however, is on the stone: characteristic pale rings or spots on the stone itself [71]. This distinguishes plum and apricot from peach. On European plums, premature fruit drop reaches 100% in susceptible cultivars.

Why insecticides do not stop spread

This is the most misunderstood point in the crop, and it has a clear biological explanation. Twenty-eight aphid vector species are recognised [72]. Transmission is non-persistent, via the stylet: acquisition occurs within a few seconds from an infected cell, the aphid retains the virus for a few hours, and no latent period is required [72].

For Greece, which vector predominates matters. Aphis spiraecola is the main vector in Mediterranean climates, while Phorodon humuli and Hyalopterus pruni predominate in continental ones; Myzus persicae is important in both [72]. EPPO independently names the same four as the main vectors [71]. The two sources agree.

Latent period and spread in space

After a tree is grafted, the incubation period may last several months and systemic spread several years [71]. Symptoms may not appear for up to three years, although serological detection is possible earlier. Therefore, from a few months to about three years between infection and visible expression.

In space, about 50% of transmission events occur within 90 metres of the source tree, with total spread covering hundreds of metres [71]. The figure comes from a single source. Its practical significance is that the neighbour's infected tree counts, and that eradication makes sense only if carried out at area level.

The scale of the cost

The above come from a 2024 open-access review [73]: direct fruit losses exceed EUR 2 billion, eradication and containment EUR 100 million, serological testing EUR 137 million and research about EUR 130 million. The virus is present on every continent except Oceania. The paper includes as co-author the researcher of the Benaki Phytopathological Institute who is the Greek authority on the subject [73].

Sharka is present in mainland Greece [71]. No Greek infection rates are cited here, nor which strain predominates in Greece, because the relevant Greek publication could not be accessed, not even in its abstract. Its title suggests strain M, but a title is not a source.

Detection, for those who need laboratory testing

• Grafting onto the peach indicator GF305 or onto Prunus tomentosa, symptoms in 6 to 8 weeks [71].
• Mechanical inoculation of Chenopodium foetidum or Nicotiana benthamiana, 6 to 10 days.
• ELISA: the sample is composite, from leaves of actively growing shoots, from different points of the canopy. Where the sample is taken determines the result more than the method does.

Angeleno and the «tapa», a field observation from Pella, Greece

Angeleno is among the most widely planted varieties in Greece, because it is late and holds well in cold storage. In the orchards of the region, its sharka-affected fruit show dark, irregular, sunken areas that often take a ring shape. Growers call this «tapa», and such fruit are frequently discarded through the summer as a kind of informal thinning.

The trait is practically useful because it shows on the flesh and the fruit surface, earlier and more easily than the light rings on the stone that are the classic diagnostic feature. It does not replace a laboratory test: dark sunken areas on the fruit also arise from other causes, from insect feeding to mechanical injury.

7.2 European stone fruit yellows phytoplasma

The causal agent is 'Candidatus Phytoplasma prunorum', group 16SrX-B [74]. The only confirmed vector is Cacopsylla pruni, whose biology and treatment window were given in section 4.10.

In Greece the disease is described as widespread, with documented presence in Macedonia, Thessaly and the Peloponnese, and no reports from Crete [47]. The explanation given by the authors, the absence of the preferred wild Prunus and especially of blackthorn, is at the same time the management guidance: the inoculum reservoir is the wild vegetation on the margins.

7.3 The ilarviruses: PNRSV and PDV

Prunus necrotic ringspot virus and Prune dwarf virus are two separate entries with a zero tolerance threshold in Annex IV, Part J of Regulation 2019/2072 [1].

The second takes its name from its effect on plum. Both are transmitted by pollen and by seed, are endemic in older plantings, and directly concern anyone purchasing planting material. The regulatory lever is the same as for sharka and the phytoplasma: certified material, zero tolerance.

7.4 What "certified material" means in practice

Five of the most serious plum problems, sharka, the phytoplasma, bacterial spot, PNRSV and PDV, have the same regulatory control mechanism: zero tolerance on plants for planting [1]. None of them can be dealt with after planting.

Sources: 1 3 4 47 67 68 71 72 73 74

8. What quarantine is and what it is not

This is one of the points where both the Greek and the international literature aimed at growers goes wrong, and the error has consequences: it changes what the grower is obliged to do and what the grower is entitled to expect from the state.

The three categories

Where each of the diseases in this article stands

Sources: 1 2 71 74

9. Identification from symptoms

The tool below compares the symptoms seen in the orchard against the profile of each cause described in the previous sections. It does not replace a diagnosis; it narrows the list of candidates and shows the one feature that has to be looked for in order to close the case.

Sources: 2 4 10 16 28 32 38 39 40 5 6 56 57 60 62 63 66 67 68 69 71

10. Diseases and pests that get confused with one another

The table is the tool in a form that can be read without a screen. Each row is a pair that is confused in practice, with the one feature that separates them.

Sources: 1 4 5 6 9 10 16 23 28 32 35 36 38 39 40 41 42 51 56 57 60 62 63 66 67 68 69 71

11. Monitoring: traps, sampling, thresholds

This section gathers into a single table everything documented in the preceding ones, with the distinction that matters: what is a measured threshold and what is merely monitoring. No figure is given anywhere that was not found in a source.

Sources: 1 9 10 20 21 24 25 28 29 30 33 35 36 37 38 39 40 43 49 50 56 66 71

12. What is authorised in Greece today

What follows comes from the authorisations database of the Greek Ministry of Rural Development and Food, as it stood on 14 September 2026, for the crop PLUM [75]. The crop has a total of 491 product-and-target entries.

Authorisations change. This list is a snapshot of one date and does not replace checking the label and the authorisation in force before every intervention. The updated database is available at fyto.plantprotect.gr.

The fungal and bacterial targets

The insect and mite targets

The products themselves, the trade names, the doses, the pre-harvest intervals and the growth stages of application are not listed here. They change frequently and the label is the only valid source. Searching by crop, by product, by active substance and by company is done at fyto.plantprotect.gr [75].

Sources: 8 9 22 26 75

13. The annual programme by growth stage

The table gathers the decisions of the year in the order in which they arise. It is not a spray programme: it is the list of what is judged at each stage and on what documentation. The final decision requires an on-site assessment.

Sources: 8 9 21 22 24 26 28 31 37 40 42 43 47 48 54 5 6 55 56 60 62 66 69

14. Where the subject continues

Many of the topics mentioned here have their own article, in more depth than a single section allows.

The plant protection product authorisations for every crop, active substance, product and company are found at fyto.plantprotect.gr (valid in Greece only) [75]. The official Greek pest-warning bulletins are published by the Regional Plant Protection Centres of the Greek Ministry of Rural Development and Food [9].

15. The points that remain open

An article that states only what it knows is half an article. The following were sought and not found, or were found in a form that does not stand citation. They are recorded explicitly so that no one fills them in by conjecture.

The Greek gaps

• No Greek phenological study of San Jose scale on plum. All four Greek works were carried out on almond, apricot, apple or peach [11] [12] [13] [17]. Transferring the results is reasonable, but it is not verified.
• The bulletins do not track San Jose scale phenologically on plum. There is only the recommendation of winter oil [9] [22].
• Rust does not appear in any stone fruit bulletin, and it has only two authorised products [9] [75], while in practice it requires treatment every season. There is no Greek forecasting model and no Greek wetness data for it.
• No Greek phenological study of the plum sawfly. Its presence rests on a single Greek source, which describes it as local [27].
• No Greek infection rates for sharka are cited, nor the strain that predominates in Greece. The relevant Greek publication could not be read, not even in its abstract.
• There is no Greek measurement of the number of generations of white peach scale. The "two to three" is an estimate from the climatic range of the source, not a measurement [36].

The numerical gaps

• There is no verified complete degree-day model for the plum fruit moth with a threshold, a biofix and degree-days per generation. That is why the bulletins work with traps and phenological stage [9].
• No wetness duration for scab, on any host [62].
• No duration of wound susceptibility for silver leaf [5]. Figures in days that circulate are not documented.
• No ice nucleation temperature for Pseudomonas syringae, although it is central to bacterial canker after frost.
• No numerical threshold for aphids on plum, from any source [33].
• No summer spider mite threshold specific to plum [37].
• No economic threshold for Capnodis, and the review states that the monitoring devices themselves are lacking [40].
• No number of years of survival for the microsclerotia of Verticillium wilt [69] or for Armillaria in dead roots [68]. The sources say "years" or "indefinitely".
• No published measurement of damage to plums from Halyomorpha halys [49] [50], and no quantitative susceptibility data for the Mediterranean fruit fly [45].
• No ranking of plum susceptibility to Verticillium wilt; the available source concerns cherry [69].

The open disagreements

• Generations of the plum fruit moth. Three in Thessaloniki, "four to five" in a bulletin from another prefecture, possibly a confusion with G. molesta [9]. See section 3.
• Hyalopterus pruni as a vector of sharka. One study reports it as effective up to 80% [34], the general literature as weak [32]. The question remains unresolved.
• The economic outcome of mating disruption. Two Italian studies on plum agree that the method works and disagree on whether it reduces economic damage [8] [26].
• Which pathotype of Pseudomonas syringae predominates on plum. The literature provides no answer [6] [55].
• The EPPO distribution of G. funebrana does not include Greece [7], while the Greek bulletins actively monitor it [9]. This is a missing record.
• The status of Monilinia fructicola. It is not found in the text of Regulation 2019/2072, whereas it was a quarantine organism under the previous directive.

Sources: 7 8 9 11 12 13 17 22 26 27 32 33 34 36 37 40 45 49 50 5 6 55 62 68 69 75

16. Sources

The numbers in the text refer to the list below. Each source states exactly what it documents, and wherever only an abstract or a second-hand citation was available, that is said explicitly.

Legislation and official databases

• [1] Commission Implementing Regulation (EU) 2019/2072, consolidated text. Source for: the status of each organism, Annex IV for sharka, bacterial spot, the phytoplasma, PNRSV, PDV and Verticillium dahliae, and for the fact that Chondrostereum purpureum is not listed on Prunus.
• [9] Official pest-warning bulletins, Regional Centres for Plant Protection, Quality and Phytosanitary Control, Greek Ministry of Rural Development and Food. Stone fruit bulletins from Thessaloniki, Kavala, Drama, Serres and Central Greece for 2020, 2021 and 2026. Source for: the plum fruit moth generation calendar with Greek dates, the start of peach twig borer flight in the last ten days of April, the blossom weevil in November, and for the two negative findings, that San Jose scale is not monitored phenologically and that rust appears in no bulletin at all. These are official Greek documents and are not translated.
• [22] Regional Plant Protection Centre of Volos, Stone Fruit Bulletin No 1 of 7 February 2025. Source for: the official Greek instruction that winter mineral oils are applied up to bud swell and that they also cover other overwintering insect and mite stages; also for the Greek name used for white peach scale.
• [54] ETHEAS, Technical bulletin on stone fruit protection: monitoring and control of fruit moths. Source for: independent confirmation that peach twig borer flight starts in the last ten days of April, and for the four to five generations of Grapholita molesta in Greece.
• [75] Plant protection product authorisation database of the Greek Ministry of Rural Development and Food, as recorded on 14 September 2026 for the crop PLUM, 491 product-and-target entries. Source for: the number of products and active substances per target, the double registration of brown rot under two separate names, the mere two products authorised against rust, and the existence of authorised pheromone dispensers for plum fruit moth and peach twig borer. Valid in Greece only.

EPPO databases and EFSA assessments

• [2] EPPO Global Database, datasheet for Xanthomonas arboricola pv. pruni (XANTPR). Source for: the greater susceptibility of the Sino-Japanese group, the favourable conditions of 25 to 33 °C with light rain and heavy dews, overwintering in buds, leaf scars and cankers, and the phytotoxicity risk of copper sprays.
• [3] EFSA Panel on Plant Health, Pest categorisation of Xanthomonas arboricola pv. pruni, EFSA Journal. Source for: the statement that yield and quality losses are expected on peach, nectarine and Japanese plum, while minimal damage is expected on cherry and European plum.
• [7] EPPO Global Database, hosts and distribution of Grapholita funebrana (LASPFU). Source for: plum and apricot as major hosts, and for the documented gap that the distribution record does not include Greece while the Greek bulletins monitor the species actively.
• [16] EPPO Global Database, datasheet for Diaspidiotus perniciosus (QUADPE). Source for: overwintering as a first-instar nymph, the violet-red halo appearing within 24 hours of the crawler settling, and for plum being listed as a host but not a major host.
• [43] EPPO Global Database, datasheet for Drosophila suzukii (DROSSU). Source for: establishment in mainland Greece and Crete, the 3 to 9 generations, the preference for slightly under-ripe fruit that has started to colour, the preference for red, late-harvest and soft-skinned cultivars, and the apple cider vinegar traps.
• [45] EPPO Global Database, datasheet for Ceratitis capitata (CERTCA). Source for: the explicit listing of Prunus domestica and P. salicina among the hosts with no severity grading, and for presence in mainland Greece and Crete.
• [53] EPPO Global Database, hosts of Anarsia lineatella (ANARLI). Source for: apricot and peach as major hosts with plum as a secondary host, and for the sequence of boring first into tender shoots and then into fruit.
• [65] EPPO Reporting Service, article 3367, reporting the findings of Zaccardelli, M., Malaguti, S. and Bazzi, C. (1998), Journal of Plant Pathology 80(2):125–132. Source for: recovery of the bacterium from fallen leaves, buds and leaf scars up to 6 or 7 months after contamination, and for summer cankers on plums in the Po Valley acting as overwintering sites. The EPPO report was used, not the original paper.
• [71] EPPO Global Database, datasheet for Potyvirus plumpoxi (PPV000). Source for: the ten strains, the pale rings on the stone as the diagnostic feature, premature fruit drop reaching 100%, the incubation period, the 50% of transmissions within 90 m, the main vectors, the limited effectiveness of aphicides, and the detection methods.
• [74] EPPO Global Database, 'Candidatus Phytoplasma prunorum' (PHYPPR). Source for: the identity of the pathogen, the 16SrX-B group and its status as a Regulated Non-Quarantine Pest.

Greek studies

• [11] Katsoyannos, P. and Argyriou, L.C. (1985). Biology of San Jose scale on almond in northern Greece. Source for: three generations per year, overwintering of the majority as first-instar larvae, and for Cybocephalus fodori being the key predator in northern Greece.
• [12] Navrozidis, E. et al. (1999). Control of San Jose scale on apricot in northern Greece. Acta Horticulturae 488. Source for: three generations, four generations of the parasitoid Encarsia perniciosi, the successful control by fenoxycarb, buprofezin and especially diofenolan with minimal effect on beneficials, and the detrimental effect of methidathion on the parasitoid.
• [13] Kyparissoudas, D. et al. (1987). Monitoring of San Jose scale on apple, peach and nectarine. Source for: a third independent Greek confirmation of three generations, on crops different from the two preceding studies.
• [14] Kyparissoudas, D. (1987). Crawler emergence periods of San Jose scale in northern Greece. Source for: the three crawler windows, late May to early July, mid-July to August, September to October, and for the partial fourth generation in November.
• [17] Deligeorgidis, P.N. et al. (2008). Pheromone trap monitoring of San Jose scale in apple orchards of the Florina region. Source for: the finding that pheromone traps give timing and not population density.
• [20] Damos, P.T., Soulopoulou, P., Gkouderis, D., Monastiridis, D., Vrettou, M., Sakellariou, D. and Thomidis, T. (2022). Degree-day risk thresholds for predicting the occurrence of Anarsia lineatella, Grapholita molesta and Adoxophyes orana in northern Greece peach orchards. Plant Protection Science 58(3):234–244. Pella, 2018–2021. Source for: the Greek lower temperature thresholds, 11.4 °C, 9.5 °C and 7.2 °C, and the degree-day sums per phenological event. Developed on peach, not on plum.
• [27] Mavromatis, A. (2008). Injurious insects of peach, apricot and plum: possibilities for integrated control. Diploma thesis, Technological Educational Institute of Crete. Source for: the single Greek record of the presence of Hoplocampa flava and H. minuta, and of a local one at that. A student thesis, it cannot stand alone for a quantitative claim and was not used for any.
• [49] Damos, P. et al. (2020). First record and current status of the brown marmorated stink bug Halyomorpha halys damaging peaches and olives in northern Greece. Journal of Plant Protection Research. Source for: establishment in the Imathia regional unit with samplings in 2018 and 2019, the damage on peaches and olives, and the overwintering adults in structures near the orchards. Plum is not mentioned.
• [52] Argyriou, L.C. (1981). Establishment of the imported parasite Prospaltella perniciosi on Quadraspidiotus perniciosus in Greece. Entomophaga 26(2):125–130. Benaki Phytopathological Institute. Source for: the establishment of the introduced parasitoid in Greece. Only the bibliographic record was verified; the abstract could not be retrieved.

Insects and mites

• [8] Lo Verde, G., Guarino, S., Barone, S. and Rizzo, R. (2020). Can mating disruption be a possible route to control plum fruit moth in Mediterranean environments? Insects 11(9):589. Source for: the 550 dispensers per hectare in a Sicilian plum orchard, the reduction of catches from 81.3 and 60.3 to 6 and 4.3, the residual infestation of 36 to 59% on Angeleno, and the optimal emission of about 60 days falling by 66% after 72 days.
• [10] CAPS, Purdue University, datasheets for Grapholita funebrana (2024 and the stone fruit manual). Source for: overwintering as a prepupa in a cocoon, gummosis at the entry hole, premature colouring and fruit drop, the two morphological characters separating it from G. molesta, and the statement that pheromone traps have given mixed results as a density indicator.
• [15] Survey by the Turkish Ministry of Agriculture (2017) on San Jose scale. Source for: a second Mediterranean reference point on the number of generations.
• [18] Kocourek, F. et al. (2000). Degree-day model for San Jose scale in Central Europe. Source for: the 400 degree-days above 7.3 °C from the first male catch, the European model.
• [19] Degree-day models from Virginia Tech, Cornell, the University of Kentucky and UC IPM for San Jose scale. Source for: the 300 to 400 degree-days to the start and 600 to 700 to peak movement, on a base of 10.0 to 10.6 °C, and for their incompatibility with the European model.
• [21] UC IPM, San Jose Scale, Plum and Prune. Source for: the dormant sampling of 100 fruiting spurs and the thresholds of 20 and 60% for early harvest and 5 and 10% for late harvest; also for delayed-dormant oil timing, the gum oozing from limbs and the rough bark.
• [23] Penn State Extension, San Jose Scale and Virginia Tech, San Jose Scale. Source for: overwintering as black cap nymphs, the pale bull's-eye mark revealed under the cover, and the cracking of the wood and dieback of limbs under heavy infestation.
• [24] O'Brien, F. and Berrie, A., NIAB EMR (2019). Best Practice Guide to UK Plum Production, Plum Fruit Moth. Source for: the threshold of 30 moths per trap per week, weekly monitoring from petal fall to harvest, and the cavity filled with brown frass. UK data, from a single-generation climate.
• [25] Russell IPM, Cydia funebrana, Plum Moth. Source for: the trap density of one per 2 hectares or two per hectare, the lure change every 4 to 6 weeks, and the explicit warning that spray decisions should not be taken on trap catch data alone.
• [26] Sciarretta, A. and Valentino, C. (2016). Combined mating disruption of Grapholita funebrana and Anarsia lineatella in plum orchards. Giornate Fitopatologiche. Source for: the 600 dispensers per hectare for one species and 760 for the combination, the results of 0.1% against 1.31% in 2014 and 0.4 to 1.2% against 10.1% in 2015, placement on the block margins before flight, and for the severe peach twig borer damage on plum cultivars grown for drying.
• [28] AGES, Austrian Agency for Health and Food Safety, Plum sawfly. Source for: one generation per year, adult emergence just before flowering, the use of white sticky traps from one week before to one week after flowering, the threshold of 4 to 8 egg deposits per 100 calyxes or 2 to 6% of fruitlets, the five fruits damaged per larva, and the treatment immediately after flowering.
• [29] Shevchuk, I. and Shevchuk, O. (2022). Which Color Is Better? Efficiency of Color Traps for Monitoring of Black Plum Sawfly. Biology and Life Sciences Forum 16(1):18. Source for: the 89 adults per white trap against 10 for yellow and blue, the 53 to 62% of the total and up to 80% at peak, placement at 1.2 m, the flight starting 31 to 42 days from the beginning of bud swelling, and the flight duration of 17 to 34 days.
• [30] Karpati, Z., Bognar, C., Voigt, E., Toth, M. and Molnar, B.P. (2021). Monitoring of three Hoplocampa sawfly species in plum orchards. Acta Phytopathologica et Entomologica Hungarica 56(2):143–152. Source for: the use of white chromotropic traps in three plum orchards, the maximum catches of 146 and 80 individuals, and the explicit statement that no damage thresholds were established.
• [31] AgroAtlas, Hoplocampa flava. Source for: adult emergence one to two days before the beginning of blossoming, the roughly six fruits injured per larva, the crop losses of 30 to 80% in Crimea, the two treatments at balloon stage and immediately after blossoming, and the autumn ploughing. Greece is not named in the distribution.
• [32] InfluentialPoints, Hyalopterus pruni and Brachycaudus helichrysi. Source for: migration to reeds in early July to early August and the return in September and October, leaf rolling perpendicular to the mid-rib, the observation that rolling by H. pruni occurs only on very young leaves, and for the description of H. pruni as a weak vector of plum pox.
• [33] PNW Insect Management Handbook, Plum and prune, Aphid. Source for: the migration of Phorodon humuli to hops in May, the stunting and malformation of young trees, the sooty mould on the fruit, the start of shoot inspection before budbreak, and for the absence of any numeric threshold.
• [34] Isac, M., Preda, S. and Marcu, M. (1998). Aphid species, vectors of plum pox virus. Acta Virologica 42:233–234. Romania, seven plum cultivars. Source for: the ranking of Phorodon humuli as the most efficient vector at 80%, and 100% on the cultivar Vanat romanesc, and for the range of 20 to 60% and 40 to 80% by cultivar susceptibility.
• [35] Fera and Defra, Plant Pest Factsheet: Sphaerolecanium prunastri, June 2016. Source for: the strong preference for Prunus domestica, one generation per year, overwintering as second-instar nymphs, egg hatch in late June, and the copious honeydew. Greece is not named explicitly.
• [36] Defra, Plant Pest Factsheet: Pseudaulacaspis pentagona, revised June 2016. Source for: the explicit listing of Greece in the distribution, overwintering as the adult female, the one to four generations depending on climate, the drying out of twigs and whole trees, and the recognition of crawlers as a dusty appearance on the sticky tape.
• [37] UC IPM, European Red Mite, Plum. Source for: overwintering as eggs on the spurs, the numerous overlapping summer generations, the dormant spray threshold of 20% of spurs carrying eggs, and for the recommendation to treat in summer only when foliage damage appears.
• [38] CDFA, Pest Rating Proposal: Acalitus phloeocoptes, 2019. Source for: the restriction to Prunus and Cotoneaster, the damage on almond, apricot and plum, gall formation under the bud scales, the multiple generations and 700 to 850 eggs per female, and for the winter removal of infested twigs.
• [39] PNW Insect Management Handbook, Plum and prune, Rust mite. Source for: upward curling of mature leaves, the brown or bronze scurfy lower surface, overwintering as adult females under the bud scales, the 6 to 22 day generation, the need for a 20x lens at least, and for the explicit statement that the impact on vigour and yield is uncertain.
• [40] Nasouri, H. (2024). Capnodis tenebrionis, an important pest of stone fruits in the Mediterranean basin: current management strategies and prospects for integrated pest management. Journal of Integrated Pest Management 15(1):20. Source for: the explicit listing of plum among the hosts, adult longevity of more than one year and larval development of 6 to 18 months, egg laying from 23 °C with an optimum of 30 to 34 °C, the link between irrigation and infestation severity, the entomopathogenic nematode results, and for the absence of economic thresholds and of monitoring devices.
• [41] forestpests.eu, Zeuzera pyrina. Source for: the two-year cycle, the galleries of about 20 cm, and the absence of any outbreak tendency. Plum is not named among the hosts in this source.
• [42] PNW Insect Management Handbook, Plum and prune, Shothole borer. Source for: the attack on plum, the association with stressed plants and with neighbouring neglected orchards or infested wood piles, the exit holes of about 2 mm, the two generations, the inspection in late spring, and for the recommendation that the best management tool is keeping trees healthy.
• [44] Lee, J.C., Bruck, D.J., Curry, H., Edwards, D., Haviland, D.R., Van Steenwyk, R.A. and Yorgey, B.M. (2011). The susceptibility of small fruits and cherries to the spotted-wing drosophila. Pest Management Science. Source for: the 7% of eggs laid on plums against 73% on cherries. A second-hand report of a Japanese study inside the paper; the study itself did not test plum.
• [46] USDA APHIS, Medfly Host List, January 2017. Source for: the second independent record of Prunus domestica and P. salicina as hosts of the Mediterranean fruit fly.
• [47] Steffek, R., Follak, S., Sauvion, N., Labonne, G. and MacLeod, A. (2012). Distribution of 'Candidatus Phytoplasma prunorum' and its vector Cacopsylla pruni in European fruit-growing areas: a review. EPPO Bulletin. Source for: the disease being widespread in Greece with documented presence in Macedonia, Thessaly and the Peloponnese, the absence of reports from Crete and the explanation offered for it, the univoltine cycle with aestivation on conifers, and for the effective latency of eight months that makes the remigrant adults the dangerous ones.
• [48] Labonne, G. and Lichou, J. (2004). Data on the life cycle of Cacopsylla pruni, Psyllidae vector of European stone fruit yellows phytoplasma, in France. Acta Horticulturae 657:465–470. Source for: the independent confirmation that remigrants are found on Prunus from February to May and the new generation from May to June, and that blackthorn is the preferred host plant.
• [50] Maistrello, L., Caruso, S. and Tommasini, M.G. Bioecology and management of Halyomorpha halys in fruit orchards. Ecofruit, pp. 199–202. Source for: up to 60% of fruit damaged under integrated management and over 90% under organic, the 80 to 100% yield losses in 2019, the two generations in Italy, the exclusion netting, and for the finding that aggregation pheromone traps indicate presence and not density. It concerns pear, peach, nectarine and hazelnut, not plum.
• [51] WSU Tree Fruit, Oriental Fruit Moth. Source for: plum as a host of G. molesta, the three to four flights, the lower threshold of 7.2 °C in the US model, and for shoot damage in the first and second generations and fruit damage in the third and fourth.

Diseases

• [4] Cieślińska, M. (2011). European stone fruit yellows disease and its causal agent 'Candidatus Phytoplasma prunorum'. Journal of Plant Protection Research 51(4):441–447. Source for: the susceptibility ranking, apricot, Japanese plum, peach, European plum, sweet cherry, and specifically for the high tolerance of P. domestica.
• [5] O'Brien, F. and Berrie, A., NIAB EMR (2019). Best Practice Guide to UK Plum Production, Silver Leaf. Source for: Chondrostereum purpureum affecting principally plum and cherry, the silvering being caused by a mycotoxin rather than colonisation of the leaf, entry mainly through pruning wounds, spore production being greatest in autumn and winter, and for the recommendation to prune in late spring with burning of the wood and disinfection of tools.
• [6] O'Brien, F. and Berrie, A., NIAB EMR (2019). Best Practice Guide to UK Plum Production, Bacterial Canker. Source for: leaf scars as the principal infection route, the cycle with an epiphytic spring phase, the latency of up to 18 months, the gum exuding from shallow hollows, and for the recommendation to prune in prolonged dry weather in May or June.
• [55] Hulin, M.T. et al. (2018). Characterization of the pathogenicity of strains of Pseudomonas syringae towards cherry and plum. Plant Pathology 67:1177–1193. Source for: the host specialisation of pv. morsprunorum race 1 on plum, the confirmation of the leaf scar as the standard infection court, and for the difference in susceptibility between the cultivars Victoria and Marjorie's Seedling.
• [56] PNW Plant Disease Management Handbook, Prune and Plum, Brown Rot. Source for: overwintering in mummified fruit, the fruit susceptibility curve from bloom through pit hardening and rising again at ripening, the latent infection, and for the treatment windows at early popcorn, full bloom and petal fall.
• [57] CDFA, Pest Risk Profile: Tranzschelia discolor. Source for: the identity of T. pruni-spinosae var. discolor with T. discolor, the macrocyclic heteroecious cycle with Anemone coronaria, the finding that the alternate host is not necessary, the 12 to 18 hours of wetness, and for the twig canker lesions of 3 to 6 mm.
• [58] AHDB SCEPTREplus, CP 165 SP41 Plum Rust, final report, reporting the findings of Ellison et al. (1990) and D'urban-Jackson (2018). Source for: urediniospore germination between 5 and 30 °C with over 80% within 2 hours, the latent period of 15 to 21 days, and the qualitative moisture criteria. Second-order citations through an unpublished thesis, used with an explicit reservation.
• [59] O'Brien, F. and Berrie, A., NIAB EMR (2019). Best Practice Guide to UK Plum Production, Plum Rust. Source for: symptoms appearing in July and delayed to August, the reduction in the carbohydrate reserve and in next season's yield, the late spring treatment, and for the UK resistant cultivars.
• [60] PNW Plant Disease Management Handbook, Peach, Shothole. Source for: dormant-season infection requiring continuous moisture for at least 24 hours above 2.2 °C and only 6 hours at 25 °C in the growing season, the polycyclic nature, overwintering in buds and twigs with cankers as the primary spore source, the lesions up to 6 mm with gummy exudate, and for the sprays at 50% leaf fall and at shuck fall.
• [61] Shaw, D.A., Adaskaveg, J.E. and Ogawa, J.M. (1990). Influence of wetness period and temperature on infection and development of shot-hole disease of almond caused by Wilsonomyces carpophilus. Phytopathology 80:749–756. Source for: conidial germination of 85.3% in 4 hours and 99.2% in 8, the 0.1 against 45.0 lesions per leaf at 8 and 22 °C after 14 hours of wetness, and the 72.0% abscission at 22 °C. The study was done on almond and concerns leaf infection only.
• [62] Kim, G.H., Jo, K.Y., Shin, J.S., Shin, G.H. and Koh, Y.J. (2017). Epidemiological characteristics of scab of Japanese apricot in Korea. The Plant Pathology Journal 33(5):450–457. Source for: the optimum temperature of 20 to 27 °C, the latent period of 42 to 77 days with 55 days in the field, two-year-old branches as the primary inoculum source, conidial dispersal from late March to late April, and for effective control from mid-April. The study was done on Japanese apricot, not on plum.
• [63] Defra Plant Health Portal, Plant Pest Factsheet: Xanthomonas arboricola pv. pruni, 2023. Source for: the angular spots with a pale halo and the sunken cracked fruit spots up to 10 mm, the perennial cankers on plum and apricot, the spread by rain splash, and for the avoidance of overhead irrigation. The "notifiable disease" status applies to Great Britain and does not transfer to Greece.
• [64] Morales, G., Moragrega, C., Montesinos, E. and Llorente, I. (2018). Effects of leaf wetness duration and temperature on infection of Prunus by Xanthomonas arboricola pv. pruni. PLOS ONE 13(3):e0193813. Source for: the optimum infection temperature of 28.9 °C, the range of 5 to 35 °C, the more than 10 hours of wetness near 20 °C and 5 hours at 25 to 35 °C, and for the model agreeing with observations in 92% of validation cases. The authors themselves state that the study used only a peach-almond hybrid rootstock, not plum.
• [66] Biggs, A.R. and Grove, G.G. (2005). Leucostoma canker of stone fruits. The Plant Health Instructor, vol. 5. Source for: plum as a major host, the infection courts of leaf scars, dead buds and early-dormant pruning cuts, infection at 14 to 20 °C with greater colonisation at 2 to 8 °C, conidial dispersal at 10 to 15 °C with humidity above 90%, the dead twig at the canker centre as the diagnostic feature, and for the recommendation to prune in late spring.
• [67] UC IPM, Plum, Phytophthora Root and Crown Rot. Source for: the threshold of 24 hours of saturated soil, the lower susceptibility of plum rootstocks compared with peach rootstocks, and for the explicit reservation that no rootstock is resistant to all pathogenic species.
• [68] UC IPM, Plum, Armillaria Root and Crown Rot. Source for: the white fan-shaped mycelial mats and the black rhizomorphs as definitive diagnostic signs, the partial tolerance of Marianna 2624, the crown excavation of 23 to 30 cm, and for the 1.2 m trench with a plastic barrier.
• [69] PNW Plant Disease Management Handbook, Cherry, Verticillium Wilt. Source for: the red-brown streaking in the sapwood and the asymmetric pattern in which some branches stay healthy, the indefinite survival of microsclerotia with no figure in years, the recommendation not to plant an orchard after solanaceous crops, strawberry or raspberry, and for the restriction of nitrogen. The page concerns cherry.
• [70] UC IPM, Eutypa Dieback. Source for: the disease affecting apricot and grape and sporadically cherry, with plum absent from the host list; also for the 355 mm of annual rainfall, the duration of wound susceptibility, and for pruning apricot and cherry only in July and August.
• [72] Cambra, M. and Vidal, E. (2017). Sharka, a vector-borne disease caused by Plum pox virus: vector species, transmission mechanism, epidemiology and mitigation strategies to reduce its natural spread. Acta Horticulturae 1163:57–68. Source for: the 28 aphid vector species, the non-persistent stylet-borne mechanism acquired in seconds with no latent period required, the dominance of Aphis spiraecola in Mediterranean climates, and for the finding that insecticides do not stop spread because transmission occurs faster than pesticide lethality.
• [73] Cambra, M., Madariaga, M., Varveri, C., Çağlayan, K., Morca, A.F., Chirkov, S. and Glasa, M. (2024). Estimated costs of plum pox virus and management of sharka, the disease it causes. Phytopathologia Mediterranea 63(3):343–365, open access. Source for: the EUR 2.4 billion for 1995–2023, the cumulative losses above EUR 13 billion, the breakdown into direct losses, eradication, testing and research, and for the presence in 54 countries. A researcher of the Benaki Phytopathological Institute is a co-author.
• [76] UC IPM. Silver Leaf, Chondrostereum purpureum. University of California Agriculture and Natural Resources. Source for the fungal toxin being carried to the leaves through the xylem.