Apricot pests and diseases: identification from symptoms, with a diagnostic tool
Savvas Pastopoulos, Agronomist MSc, Pastopoulos Agronomics, Neos Mylotopos, Pella, Greece
Apricot is the most vulnerable of the stone fruits. It flowers first and pays for frost, it closes wounds slowly and pays for pruning, and it collapses as a whole tree instead of declining gradually. What follows covers the pests and diseases of the crop with the emphasis on telling them apart, that is not what exists but how one is distinguished from another in the field, with a diagnostic tool that compares symptoms against the profiles of thirty-four causes.
- The particular features of apricot
- The identification tool
- Rust
- Fungi of the blossom and the fruit
- Leaf spots
- Bacterial canker and the pruning dilemma
- Wood diseases
- Crown, roots and vascular diseases
- Viruses and phytoplasmas
- Moths and flies of the fruit
- Sucking and wood-boring pests
- Damage that is not disease
- Causes that are confused with one another
- The annual monitoring calendar
- Sources
1. The particular features of apricot
Four characteristics of the crop change how every attack is read, and all four work against the grower.
It flowers first. Apricot opens its blossom before any other stone fruit, in a window that in Northern Greece still delivers frosts. That means two things. The first is the frost itself. The second, less obvious, is that flowering coincides with the March rains, so brown rot infection of the blossom finds open flowers exactly when the weather helps it. In the Italian literature blossom brown rot is described as the most formidable adversity of apricot, able to wipe out the crop and to kill the tree [4].
Slow healing of wounds. Apricot wood heals slowly and pruning cuts stay open as entry points for a long time. Eutypa, silver leaf and the Botryosphaeria species all come in that way. Section 6 sets out the specific problems.
It collapses instead of declining. On apple or kiwifruit a vascular infection gives years of weakening before it reaches death. On apricot the tree stands apparently well and then wilts entirely within a fortnight, often with the leaves still attached. That picture is called apoplexy, it describes the end and not the cause, and that is why it is dangerous as a diagnosis.
Defoliation damage shows the following season. Rust does not spoil the hanging fruit. It strips the canopy in July and August, that is exactly when the tree fills its reserves and differentiates flower buds. After severe early rust infection, the reduction of next season's cropping potential reaches 45% [2]. A grower who lets rust run because the apricots are already picked pays for it the following June.
2. The identification tool
The tool compares the selected symptoms against the profiles of thirty-four pathogens, pests and physiological disorders of apricot. It does not simply count how many match. Each symptom carries a weight proportional to how distinctive it is, so rust-coloured powder on the lower leaf surface counts for far more than general defoliation, which fits eight causes.
Some symptoms also count against a cause. Dead flowers that stay stuck to the spur argue for brown rot and against frost, which drops them. A tunnel that stops just under the fruit skin argues for peach twig borer and against oriental fruit moth. Without negative weights the tool does not diagnose, it merely agrees with whatever is selected. They are used only where one symptom genuinely excludes another, not where it is merely less common.
Choose an organ, then tick whichever symptoms are observed. Results update automatically.
Sources: 1 2 3 4 5 6 6 7 8 9 10 11
3. Rust
Stone fruit rust is caused by Tranzschelia discolor. It is the disease that goes unnoticed more than any other, because it appears after the fruit is picked and because the grower sees leaves rather than a crop.
How it is recognised
The picture has two faces and both must be seen. On the upper surface pale chlorotic spots appear, turning bright yellow and angular, and later developing a necrotic centre with a yellow halo [2]. On the lower surface, directly opposite each spot, uredinia form as pustules of rust-coloured powder that comes off on a finger. The correspondence between the two faces is the diagnostic feature, and no other leaf spot of apricot gives it.
On the fruit the infection gives small brown lesions of about two and a half millimetres with a greenish halo, which sink as the fruit matures and extend several millimetres into the flesh [2]. On the current season's shoots water-soaked lesions develop into splits, and uredinia form inside the splits [2]. Those splits are where next season is decided.
Overwintering and its relation to the sprays
In regions with a mild winter, such as Greece, the fungus does not need the alternate host. Urediniospores overwinter inside the twig splits and in the uredinia of leaves that remain [2]. The inoculum is therefore already on the tree when the buds open, and does not arrive from elsewhere.
The alternate host of Tranzschelia discolor, where it has been documented, is Anemone coronaria [2]. That species is native and very common in Greek fields and on orchard margins, far more widespread than in California where its role was described.
No Greek study was found that examines whether anemone acts as a source of primary inoculum in Greek orchards. The connection remains a hypothesis and not a finding, and it is mentioned because it is the kind of question that one spring observation answers, by looking at whether anemone leaves around infected trees carry aecia.
The infection conditions
The model used for rust on apricot sets the temperature range at 5 to 30 °C, with an optimum of 15 to 25 °C, and calls for 18 to 36 hours of wetness at 15 to 20 °C for ideal infection [1]. The number of hours is what explains why the disease explodes after two days of rain in late spring and stays quiet through the dry summer.
The disease becomes visible in summer, but it is decided earlier, at two moments.
At winter pruning, where one-year shoots are inspected for splits carrying rust-coloured powder and whatever is found is removed. And at every prolonged spring wetting period of more than eighteen hours inside the optimum range. In an orchard with a history, those are the episodes that decide the season.
4. Fungi of the blossom and the fruit
Brown rot, blossom blight and fruit rot
Brown rot has two episodes and the first is the serious one. Blossom blight in spring removes the crop before it is formed, and moving from the flower into the spur it kills wood. The pathogens are Monilinia laxa and M. fructigena, with M. fructicola having spread [17].
Two numbers set the timing. Blossom infection is completed in 18 hours at 10 °C and in 12 hours at 16 °C, with the petals as the entry point, and first symptoms appear in 3 to 6 days [3].
Blossom brown rot is confused with two other things, with frost at flowering and with bacterial canker, and the distinction is settled at four points, all of them observed on the same spur and without a laboratory.
The fate of the dead flowers. Flowers killed by brown rot stay attached to the spur and dry out on it, whereas frost drops them [3]. This is the first feature to check, because it separates the two causes with nothing else needed.
The direction of the necrosis. With brown rot the necrosis starts at the twig tips, that is at the point where the flower sat, and advances inward. With bacterial canker it starts at the base of the branch [3]. The difference has a practical consequence too, because it sets where the cut falls when removal of the infected wood is decided.
The delimitation of the attack. Brown rot leaves a dead length with a clear boundary, with vigorous growth and fruit immediately beyond the point where it stopped, as the two images above show. A dieback that fades out gradually, with no sharp boundary, turns the suspicion toward the wood diseases of section 7.
The distribution within the tree. Radiation frost strikes from below upward, so the damage appears in a band of height and the low branches suffer more than the high ones. Brown rot leaves healthy flowers next to dead ones on the same branch, with no relation to height. That feature is developed in section 12.
The four features do not exclude one another, because on apricot the causes often coexist on the same tree and bacterial canker follows frost. The reading is made on the whole picture and not on a single symptom.
The whole disease, with the spray windows and resistance management, is in the article on brown rot of stone fruit.
Scab
Scab, Venturia carpophila with the anamorph Cladosporium carpophilum, gives small dark olive velvety spots on the fruit, concentrated near the stem end. Conidial germination has an optimum of 18 to 24 °C, with the infection range running from 7 to 24 °C [1]. The subject is covered in the article on scab on apricots.
Powdery mildew
On apricot powdery mildew is caused mainly by Podosphaera tridactyla, and the Italian recommendations place the period of susceptibility from bud break to pit hardening [5]. It is the only disease on this list that does not require wetness. The optimum is 21 to 27 °C and growth slows above 28 °C [1].
5. Leaf spots
Shot hole
Shot hole, Wilsonomyces carpophilus under the older name Stigmina carpophila, is the leaf spot a grower recognises by the holes on the leaf. The lesion starts red, its centre turns brown and necrotic, and finally drops out leaving a hole as if made by shot [15]. On the fruit it gives sunken lesions that develop into brown leathery scales, often with gum exudation [15].
The agricultural warning bulletin for apricot issued by the Regional Centre of Thessaloniki places the intervention just before bud swell, at stages A to B, and only in orchards with documented infections in the two preceding years [15]. That second condition is the one usually ignored, and it is why the spray is made in orchards that do not need it.
Spore germination needs only six hours of moisture at 25 °C, growth continues above 2 °C, and the wetness requirement for infection at low temperatures rises to 24 hours [1]. That tolerance of cold is why shot hole works through the winter and early spring, when nothing else does.
Bacterial spot
Xanthomonas arboricola pv. pruni gives angular lesions, delimited by the veins and water-soaked at first. The optimum range is 10 to 28 °C and infection is favoured by frequent light rainfall, strong wind and heavy dew [1].
The hole in the leaf separates nothing, because both causes produce it. The distinction is settled at four other points.
First, the shape of the lesion before its centre drops out. In shot hole it is round and its outline follows nothing. In bacterial spot it is angular, because spread stops at the veins. The consequence is that the lesion is read while it is still closed, and a leaf full of finished holes no longer answers the question.
Second, the appearance of the lesion at the earliest stage. In shot hole it starts red and its centre turns brown, with a pale necrotic centre and a purple halo [15]. In bacterial spot it starts water-soaked [1], so the first impression is translucency rather than colour.
Third, the distribution within one tree. Wind drives the bacterium, so the attack concentrates on the windward side and the opposite side stays almost clean. Shot hole makes no such distinction and appears evenly through the canopy.
Fourth, the season of first appearance. Shot hole works in the cold, since its growth continues above 2 °C and infection occurs even with 24 hours of wetness at low temperatures [1], so the first lesions are present from the end of winter. Bacterial spot needs a range of 10 to 28 °C [1] and rises later, with the frequent light rain, strong wind and heavy dews of spring.
In an orchard where both are present, the order of appearance through the season is often a safer feature than the shape, because the shape is lost as soon as the centre of the lesion drops out.
6. Bacterial canker and the pruning dilemma
Bacterial canker is the disease that kills young apricot trees. The pathogen most often isolated on apricot is Pseudomonas syringae pv. syringae [6]. The damage concentrates in the first years of the planting [4].
Why the presence of the bacterium is not enough
The bacterium overwinters in infected buds and inside cankers, and spends most of the year in an epiphytic phase, living on the plant without infecting it. Populations peak in spring and autumn and fall with summer heat [6]. The door is opened by heavy rainfall, by spring frosts, and by the ice-nucleating activity of the bacterium itself, which nucleates ice inside the tissues [6].
Frost is not merely a predisposing factor that happens to coincide. The bacterium itself makes the ice form at temperatures at which the tissue would otherwise not freeze [6]. A tree with a high epiphytic population suffers frost damage on a night that would have been harmless to a clean tree.
The practical consequence is that on apricot the management of bacterial canker and protection against spring frost are not two separate subjects. They are the same subject seen from two sides.
The picture on the fruit
On the fruit the infection gives brown-red necrotic lesions that make the produce unmarketable [6], documented on fruit of the cultivar Lady Cot [7].
The same documentation shows immature apricots of the cultivar Farbaly with a light epidermal russeting of red to wine colour, and states explicitly that this symptom occurs occasionally in certain cultivars and is not associated with the presence of phytopathogenic pseudomonads [7].
The observation matters because the two pictures look similar in a photograph and are entirely different in consequence. The cultivar feature is diffuse, superficial and uniform over the fruit surface. The bacterial lesion is discrete, necrotic and sunken.
The pruning dilemma
Here two diseases with opposite requirements meet, and the answer is not a compromise but a choice of season.
For bacterial canker, the Italian recommendation is to avoid pruning from October to January and to prune in July and August, disinfecting tools frequently [6]. Whatever the season, pruning is always done in dry weather and never in rain or with moisture on the wood, because the fresh cut is the entry point and water is the carrier.
For Eutypa dieback, the recommendation is the same and the reasoning independent. Eutypa lata infects fresh pruning wounds only during autumn and winter rainfall, so pruning is placed in July and August after harvest, and ideally completed at least six weeks before the first autumn rains [10].
A bacterium and a fungus, with different biology and a different entry route, point independently at the same window. Summer pruning of apricot is not a matter of school preference, it is the point at which the two most serious wood risks are minimised at once.
The cost is real, and it is larger under Greek conditions. Summer pruning triggers regrowth, because the tree is in full activity and answers removal with new shoots that spend reserves and thicken the canopy in midsummer. It also takes more labour, and in young plantings it delays the framework.
In a young orchard the balance may tip toward winter pruning. In a bearing orchard with a history of scaffold dieback, it does not.
The whole disease, with symptoms by organ and management, is in the articles on bacterial canker on apricots and on bacterial canker of stone fruit.
7. Wood diseases
Eutypa dieback and Botryosphaeria cankers
The picture of Eutypa dieback is characteristic and easily misread. Scaffolds or twigs wilt and die suddenly in late spring or summer with the leaves still attached [10]. The bark takes a dark discoloration with amber-coloured gumming, and in section the xylem and cambium appear brown [10].
The distinction from the Botryosphaeria species is one of timing. Eutypa lata infects only with autumn and winter rainfall, whereas Botryosphaeria also infects after spring or summer pruning followed by irrigation [10]. That means summer pruning, which solves the Eutypa problem, does not automatically solve the second one, and that after a summer cut, irrigation that wets the wounds is the wrong combination.
When removing, the cut is made at least thirty centimetres below the visible internal limit of the discoloration [10]. What matters is that the limit is measured in the cut and not on the bark, because discoloration of the wood always runs further down than the outside suggests.
Silver leaf
Chondrostereum purpureum gives the leaves of a whole scaffold a silvery metallic appearance, without spots and without pustules. The effect is optical and not pigmentary, because the toxin of the fungus separates the epidermis from the underlying parenchyma and the air space that forms reflects the light.
Entry is through wounds exposing wood, with the greatest susceptibility in the first week after injury. On apricot, which closes wounds slowly, that window is in practice longer than on other species.
Verticillium wilt
The microsclerotia of Verticillium dahliae survive in the soil for many years. The first symptom is the sudden wilting of one or more scaffolds in the heat, and the feature that closes the diagnosis is the brown ring or arc in the wood in a cross section of a branch, while the crown and the roots stay clean.
The history of the plot weighs more than the symptom. A previous crop of cotton, tomato or pepper on the same ground is a strong indication, and in the Greek plain that combination is common.
Both dry a scaffold in summer. The distinction is made with two cuts.
The cross section of the branch. Verticillium gives a brown ring or arc all the way round, like a line in the wood. Eutypa gives a brown wedge, asymmetric, pointing in one direction.
The longitudinal cut toward the base of the scaffold. With Eutypa the wedge continues and ends at an old pruning wound, which is the entry point. With Verticillium it ends nowhere, because the pathogen came from the root.
Sources: 10
8. Crown, roots and vascular diseases
Phytophthora crown and root rot
The zoospores of Phytophthora species infect the fine roots, and prolonged wetting of the crown from flooding or rain gives crown rot. The feature is a brown discoloration of the bark with a sharp margin against healthy tissue, which is visible only if the outer layer is pared away with a knife.
The distribution in the field is a stronger indication than the symptom itself. Damage in patches, at the low points or along the irrigation line, is the typical picture. The subject is developed in the article on Phytophthora and crown rots in fruit trees.
Armillaria root rot
The fungus survives in the soil for many years as mycelium and as rhizomorphs. The diagnostic feature is the white mycelial fans between the bark and the wood at the crown, and no other cause gives them. The second feature is the black cords on the roots, which look like string.
The history of the plot counts. Clearing of woodland or of an old tree crop on the same ground is the main risk factor, and the attack appears on scattered individual trees rather than in patches at the low points.
Crown gall
Agrobacterium tumefaciens gives solid tissue swellings at the crown and on the roots. It is not a rot and it is not a canker, and that is the whole distinction. It is favoured by planting injuries and by nematode damage, so the critical measure concerns the nursery and the moment of establishment.
When an apricot has collapsed, the diagnosis is made with three cuts, in order.
First, at the crown. Pare the bark a few centimetres above and below soil level. White fans mean Armillaria. Brown discoloration with a sharp margin means Phytophthora. Tunnels with white legless larvae mean the flatheaded root borer. Healthy white cambium means the problem is higher up.
Second, a cross section of a scaffold. A brown ring or arc means Verticillium. An asymmetric brown wedge means Eutypa.
Third, along the scaffold to its base. If the wedge ends at an old pruning wound, the diagnosis is Eutypa. If there is an elongated canker with abundant gum and a sour smell under the bark, it is bacterial canker.
If all three cuts come back clean and the tree collapsed in spring, what remains is phytoplasma and rootstock incompatibility, and both require a laboratory or digging down to the graft union.
9. Viruses and phytoplasmas
Sharka, plum pox
Plum pox virus is the most serious virus of stone fruit and a regulated harmful organism. In Greece the dominant strain is PPV-M, of Greek origin, which is readily transmitted by aphids and constitutes the epidemic form [12].
On apricot the feature that closes the diagnosis is not in the leaf but in the stone. Yellow or pale rings on the stone, visible as soon as the fruit is opened, together with chlorotic bands or rings on the leaves, are the combination that separates sharka from every other cause of deformation [12].
European stone fruit yellows
Candidatus Phytoplasma prunorum is the cause that explains many unexplained apricot collapses. The infection is described as fairly frequent in apricot plantings, while on peach and nectarine it is rarely observed [8].
The symptoms on apricot are characteristic and easily overlooked [8].
- Premature bud break, two to three weeks earlier than normal and sometimes in December. It is the most reliable feature, because no other cause wakes the tree in midwinter.
- Smaller leaves with a conical shape and interveinal chlorosis.
- Progressive branch dieback leading to the death of the tree within a few years.
- Sudden death in early spring without previous symptoms, that is the apoplexy picture.
The course of the disease differs considerably with the rootstock, and Prunus marianna GF 8-1 together with peach and apricot seedlings give a faster decline than other rootstocks [8].
The EPPO database records Candidatus Phytoplasma prunorum in Greece as present with restricted distribution [9]. This is therefore not a risk arriving from elsewhere but an organism already here.
Transmission occurs through propagation material and in the field through hemipteran insects [8]. The practical consequence is that the defence lies in certified material and in the prompt removal of infected trees, and not in any spray.
Phytoplasma and plum pox virus are not diagnosed from symptoms. Laboratory confirmation is required, and for regulated harmful organisms the competent phytosanitary authority alone is responsible.
10. Moths and flies of the fruit
Peach twig borer
Anarsia lineatella overwinters as a first or second instar larva in tiny cells in crotches and pruning wounds. In spring the larvae emerge and attack the shoots first and the fruit afterwards [19], and that order gives the first visible warning of the season.
On apricot the picture splits by generation, and the two generations do different damage.
The overwintering generation, emerging in spring, attacks mainly the new shoots of young trees and more rarely young fruitlets. In a young orchard the loss is not in the crop but in the training, because tips intended for the framework are lost.
The first generation is the one that reaches the fruit, and it is dealt with in late April to early May. Apricot fruit is susceptible, and the attack is found around the stem end, with the tunnel staying just under the skin and not reaching the stone.
In orchards in Pella, the first catch of peach twig borer is recorded at 70 degree-days and the peak of the first flight at 150.6, with a lower developmental threshold of 11.4 °C [13]. These figures come from peach orchards in the same area and the same seasons, that is from the climate in which apricot is also grown, and they are the closest Greek data available.
Oriental fruit moth
Grapholita molesta is recorded as a pest of Prunus, and apricot is one of its hosts [21], but its main crop is peach. On apricot the attack is secondary, and the early ripening usually outruns the generations that would reach the fruit. Its importance here lies in the shoots and in telling it apart from peach twig borer.
The picture on the shoot is the same. In the fruit it differs, because its tunnel reaches the stone and the larva feeds around the pit, leaving frass and gum at the entry.
In Pella the first catch is placed at 33 degree-days and the peak at 77.9, with a lower threshold of 9.5 °C [13]. The difference between the two thresholds, 9.5 against 11.4 degrees, means oriental fruit moth starts earlier, and on apricot ripening in June that has a direct consequence for which generation meets the fruit.
Peach twig borer and oriental fruit moth are not separated by the hole, because both usually enter at the stem end. They are separated by cutting the fruit in half.
A tunnel that runs under the skin and stops there is peach twig borer. A tunnel that goes down to the stone is oriental fruit moth. The distinction has practical meaning because the two flights do not coincide, and an orchard that treats one on the timing of the other hits neither.
Mediterranean fruit fly
Ceratitis capitata attacks ripe and ripening fruit. The feature is the sting hole with a dark halo and larvae inside the flesh, with no tunnel toward the stone.
In Northern Greece the attack on apricots is rare, because the populations of the insect build up later in the summer, when apricot has already been picked. The subject is developed in the article on the Mediterranean fruit fly.
11. Sucking and wood-boring pests
Flatheaded root borer
Capnodis tenebrionis kills apricot trees without the grower ever seeing it, because the damage is done below ground. The female lays in dry soil near the trunk, and the larvae move down and tunnel in the crown and the roots.
Egg laying starts at 23 °C with an optimum of 30 to 34 °C, and larval development lasts 6 to 18 months [14]. A few larvae kill a large tree in two years.
The whole life cycle and its management are in the article on the flatheaded root borer.
Wood-boring moths
Zeuzera pyrina and Cossus cossus open wide tunnels inside the wood, with coarse frass at the exit. The goat moth additionally gives a strong vinegar smell at the base of the trunk, from the fermenting liquids that run, and no other pest gives it. The subject is covered in the article on the goat moth.
The distinction from the flatheaded root borer is clean and concerns position. Capnodis works in the crown and the roots, below ground, with white legless larvae. The wood-boring moths work inside the trunk and the scaffolds, above ground, with caterpillars that have legs.
Bark beetles
Scolytus species leave small pinhole openings, often in rows on the bark, with fine sawdust. They are a secondary pest. They select trees that are already weakened, so their presence is an indicator and not a cause, and the right question is not what to spray but what is stressing this tree.
Aphids
On apricot aphids cause two different kinds of damage and the second is the serious one. The direct damage is curling of the tender tips and honeydew with sooty mould. The indirect one is transmission of plum pox virus, and there their importance is out of proportion to their numbers, because a few passing winged forms are enough.
The green peach aphid, Myzus persicae, overwinters under the bud scales and the winged forms leave during June and July [18]. For virus transmission what counts is not the established colony but the passage, because the virus is transmitted in a non-persistent manner, that is in seconds of probing.
Comstock mealybug
Pseudococcus comstocki has three generations a year and overwinters as an egg. The first generation hatches in April on the leaves, and the females then move to the bark and to the stem cavity of the fruit [20]. The feature is the white waxy secretion inside the stem cavity and in the bark cracks, and it is a place nobody sees unless the fruit is turned over.
San Jose scale and brown apricot scale
Diaspidiotus perniciosus gives round grey scales densely on the bark and small red spots with a scale at their centre on the fruit. The brown apricot scale, Parthenolecanium corni, is domed, shiny brown, about six millimetres, with one generation a year and overwintering as a nymph [11].
Spider mites
On apricot spider mites appear very rarely, and when they do there is almost always a specific trigger, heat with drought, dust from a dirt track, or a spray that wiped out the predatory mites. The symptom is fine stippling and bleaching with webbing on the lower surface, and European red mite has five to ten generations a year [11].
The predatory mites that hold these populations down are covered in the article on beneficial organisms.
12. Damage that is not disease
Frost at flowering
It is the first cause of crop loss on apricot, precisely because it flowers first. The diagnostic feature against brown rot is the fate of the dead flowers. Frost drops them, brown rot keeps them attached to the spur.
The second feature is the distribution in height. Radiation frost strikes from the bottom upward, so the low branches suffer more than the high ones. No pathogen gives that arrangement.
Silver leaf without a fungus
The silvery appearance of the foliage is not always caused by Chondrostereum purpureum. The same optical effect, that is separation of the epidermis from the underlying parenchyma, is also produced by non-parasitic causes, most commonly abrupt water stress, spray damage and nutritional disturbance.
How many trees. One or two scattered trees point to the fungus. A whole row or a whole block points to a common external cause, irrigation, a spray or a heatwave.
How many scaffolds. The fungus starts on one scaffold and stays there for a season or two before it spreads. The environmental cause takes the whole canopy at once.
Is there a wound. Chondrostereum needs a wound that exposes wood. If the scaffold has no pruning cut, break or injury, the likelihood of the fungus drops. Confirmation requires a cut into the scaffold, where the fungus gives discoloration of the wood while the environmental cause leaves the wood clean.
Fruit deformation
This is the same picture as the fruit deformation of peach, which is covered in the separate article on fruit deformation.
Pit split is a different matter and is recognised from the stone. The fruit splits along the suture, the stone is found broken, and the fruit weighs more than normal. It is favoured by excessive thinning and by an abrupt increase in irrigation while the pit is still soft.
13. Causes that are confused with one another
The table below is the tool in a form that can be read without a screen. Each row is a pair that is confused in practice, and the third column gives the one feature that separates them.
| Looks like | But is | The feature that separates them |
|---|---|---|
| Brown rot on the blossom | Frost at flowering | Brown rot keeps the dead flowers attached to the spur. Frost drops them, and strikes the low branches harder. |
| Brown rot on the shoots | Bacterial canker | Brown rot starts at the tips of the twigs and moves inward. Bacterial canker starts at the base of the branch, and the bark smells sour. |
| Shot hole | Bacterial spot | The shot hole lesion before its centre drops is round. The bacterial one is angular, delimited by the veins, and concentrates on the windward side. |
| Rust | Thrips or spray damage | Rust gives rust-coloured powder on the lower surface, directly opposite each spot on the upper one. The powder comes off on a finger. |
| Eutypa dieback | Verticillium wilt | In a cross section of a branch, Verticillium gives a brown ring or arc. Eutypa gives an asymmetric wedge ending at an old pruning wound. |
| Eutypa dieback | Botryosphaeria canker | The season of infection. Eutypa infects only with autumn and winter rainfall. Botryosphaeria also infects after summer pruning followed by irrigation. |
| Silver leaf from a fungus | Silver leaf of environmental origin | The fungus starts on one scaffold carrying a wound and gives discoloured wood in section. The environmental cause takes the whole canopy at once, often across several trees in a row, and leaves the wood clean. |
| Peach twig borer in the fruit | Oriental fruit moth | Cut the fruit. The peach twig borer tunnel stays under the skin. The oriental fruit moth tunnel reaches the stone. |
| Flatheaded root borer | Wood-boring moth | Position and larva. Capnodis works in the crown and roots with white legless larvae. Leopard moth and goat moth work inside the trunk with caterpillars that have legs. |
| Phytophthora crown rot | Armillaria root rot | Under the bark at the crown. Armillaria gives white mycelial fans and black cords on the roots. Phytophthora gives brown discoloration with a sharp margin, in patches where water stands. |
| Sharka on the fruit | Deformation from frost or thrips | The foliage. Sharka leaves chlorotic bands or rings on the leaves and yellow rings on the stone. Mechanical or cold damage leaves the foliage clean. |
| Phytoplasma | Eutypa dieback or bacterial canker | Premature bud break, two to three weeks early or in midwinter. No wood disease wakes the tree out of season. |
14. The annual monitoring calendar
The table is not a spray programme. It is a programme of observation, that is what is looked at in each season and why. The choice and the number of interventions are decided with the orchard's agronomist and on the basis of the approvals in force in Greece [16].
| Stage | Protection | What is observed | Why then |
|---|---|---|---|
| Winter pruning | Inoculum removal | Shoot splits with rust-coloured powder, twig cankers, mummified fruit | This is the whole of next season's inoculum, concentrated and visible. Whatever stays on the tree in January is the May epidemic. |
| Bud swell, stages A to B | Shot hole | History of shot hole over the two preceding years | The bulletin of the Regional Centre of Thessaloniki places the intervention here, and only in orchards with documented infection [15]. |
| Pink bud | Brown rot | Rain and temperature forecast for the days ahead | The last moment before the flowers open. Blossom brown rot is the most serious threat to the crop, it removes the crop before it is formed and carries on into the wood. |
| Full bloom | Brown rot | Wetness hours and temperature, dead flowers and whether they stay attached | Infection completes in 18 hours at 10 °C and in 12 at 16 °C, with the fully open flower at maximum susceptibility [3]. |
| Petal fall | Brown rot | Dead flowering spurs, gum droplets at their base | Petals that fall and lodge between the fruits are a substrate for infection. The bloom symptom shows now, 3 to 6 days after infection [3]. |
| Fruit set | Brown rot | Necrosis moving from the flower into the spur, scarring on the small fruit, aphid colonies | Brown rot continues as long as flower remains are present. It is also the window for thrips damage, and the season in which winged aphids transmit sharka in seconds of probing. |
| Fruitlet | Scab and shot hole | First lesions on the small fruit, mainly near the stem end | The target changes here. The flower has gone and brown rot with it, and from now on the fruit is the exposed organ. Scab infects from 7 to 24 °C with an optimum of 18 to 24, and shot hole needs six hours of moisture at 25 °C [1]. |
| Fruit growth | Scab and shot hole, peach twig borer | Struck shoots at the tips, lesions on the fruit, trap catches | The first generation of peach twig borer, the one that reaches the fruit, is dealt with in late April to early May. The two leaf spots continue with every rain. |
| Spring, after every two days of rain | Rust | Continuous wetness hours at 15 to 20 °C | Above 18 hours in that range, conditions for rust are ideal [1]. The symptom will show in June, the decision is taken now. |
| Pit hardening | Scab and shot hole, peach twig borer | Lesions that sink, tunnels under the skin around the stem end | The fruit grows fast and every lesion entering now will be visible at harvest. Peach twig borer enters at the stem end. |
| Before harvest | Monitoring | Stem cavity, sting holes | The mealybug hides inside the stem cavity and is not seen unless the fruit is turned over. Medfly is rare on this crop in Northern Greece. |
| July and August, after harvest | Wood | Pruning in dry weather, scaffold dieback, cuts into the wood | This is the window that minimises Eutypa and bacterial canker at the same time [6] [10], and the season when Eutypa becomes visible. |
| August and September | Rust | Intensity of defoliation and the lower leaf surface | Rust decides next season's crop, by as much as 45% [2], and it is the season when the grower has already stopped looking. |
| Autumn, leaf fall | Bacterial canker | Leaf scars, wounds, humidity | The scars are the main entry point and the bacterial populations peak exactly then [6]. |
| December and January | Inspection | Buds breaking out of season | This is the one phytoplasma feature that resembles nothing else [8], and it is visible only in this window. |
One line divides the season in two. From petal fall to the fruitlet stage the target is brown rot, because as long as flower remains are present there is a substrate for infection, and the necrosis moves from the flower into the wood.
From the fruitlet stage onward the target becomes scab and shot hole, because the fruit is now the exposed organ and the lesions that enter at this point will be in the tray at harvest. Between the two, rust works on its own criterion, the wetness hours, and not on the phenological stage.
15. Sources
The numbers in the text refer to the list below.
- [1] Pessl Instruments, Disease models for apricot, mirabelle and plum. Full text of page. Source for the rust temperature range of 5 to 30 °C with an optimum of 15 to 25 °C and for the 18 to 36 hours of wetness, for the scab optimum of 18 to 24 °C with an infection range of 7 to 24 °C, for the 6 hours of moisture at 25 °C and the 24 hours at low temperatures for shot hole, for the bacterial spot optimum of 10 to 28 °C, and for the powdery mildew optimum of 21 to 27 °C.
- [2] Mancero-Castillo D., Sarkhosh A., Ligon C., Olmstead M., Harmon P. (2018). Peach Rust (Tranzschelia spp.). HS1263, UF/IFAS Extension, University of Florida. Full text. Source for the chlorotic spots turning bright yellow and angular, for the fruit lesions of about 2.5 mm with a green halo sinking several millimetres into the flesh, for the water-soaked stem lesions and splits bearing uredinia, for overwintering of urediniospores in twig splits and leaf uredinia without need of the alternate host, for Anemone coronaria as the alternate host, and for the reduction of next season's cropping potential by up to 45%.
- [3] Moniliosi dell'albicocco, diradare i fiori aiuta la difesa. Terra e Vita, Edagricole, in Italian. Full text. Source for blossom infection in 18 hours at 10 °C and 12 hours at 16 °C, for the petals as entry point and maximum susceptibility at the fully open flower, for first symptoms in 3 to 6 days, for the mycelial optimum around 25 °C in a range of 2.5 to 30 °C, for spore survival beyond twenty days, for the distinction from bacterial canker based on the direction of necrosis, and for the 81% reduction of infected shoots with mechanical blossom thinning and 38 to 63% with petal removal.
- [4] Aldini A. (2009). Albicocco e susino bio, le avversità più temibili. Apofruit Italia, Pievesestina di Cesena, Frutticoltura, June 2009, via Regione Emilia-Romagna, in Italian. Full text. Source for blossom brown rot being described as the most formidable adversity of apricot, for the leaf scorch primary infection period from mid-April to mid-May and its symptoms on leaves and fruit, and for the concentration of bacterial canker damage in the first years of the planting.
- [5] Foschi S. (2025). L'albicocco e la sua difesa oggi, strumenti e possibilità. Ri.Nova, Cesena, FruitJournal, in Italian. Full text. Source for Podosphaera tridactyla as the cause of apricot powdery mildew and for the susceptibility period from bud break to pit hardening, for ascospore release of Apiognomonia erythrostoma during rain events at bud swell, and for the earwig as a nocturnal pest requiring night-time intervention.
- [6] Albicocco, deperimento batterico sempre più preoccupante. Terra e Vita, Edagricole, in Italian. Full text. Source for Pseudomonas syringae pv. syringae as the species most often found on apricot, for overwintering in buds and cankers, for the epiphytic phase and the brief infective phase, for population peaks in spring and autumn and their reduction by summer heat, for heavy rain, spring frost and ice-nucleating activity as predisposing factors, for the brown-red fruit lesions, and for the recommendation to avoid pruning from October to January and move it to July and August.
- [7] Cancro batterico dell'albicocco, dalla diagnosi alla difesa. L'Informatore Agrario 8/2019, page 33, in Italian. Source for the necrotic lesions caused by Pseudomonas syringae pv. syringae on fruit of the cultivar Lady Cot, and for the explicit statement that the light epidermal russeting of red to wine colour on immature fruit of the cultivar Farbaly occurs occasionally in certain cultivars and is not associated with the presence of phytopathogenic pseudomonads. Only page 33 was used, as supplied by the author of this article. The full text was not accessible.
- [8] Giallumi delle drupacee. Servizio Fitosanitario, Regione del Veneto, in Italian. Full text of page. Source for the frequency of phytoplasma infection in apricot plantings against its rarity on peach and nectarine, for premature bud break two to three weeks early or in December, for smaller leaves with conical shape and interveinal chlorosis, for progressive branch dieback and sudden death without previous symptoms, for the dependence of disease progression on the rootstock and the faster decline on Prunus marianna GF 8-1 and on seedlings, and for transmission through propagation material and by hemipteran insects.
- [9] EPPO Global Database, Candidatus Phytoplasma prunorum (PHYPPR), world distribution. Updated 4 March 2026. Source for the record of the organism in Greece with the status present, restricted distribution.
- [10] Eutypa Dieback and Bot Canker, Apricot. UC Statewide Integrated Pest Management Program. Full text. Source for the sudden wilting of limbs in late spring and summer with leaves still attached, for the dark bark discoloration with amber gumming and brown xylem and cambium, for Eutypa lata infecting only with autumn and winter rainfall against Botryosphaeria infecting after spring or summer pruning followed by irrigation, for the recommendation to prune in July and August after harvest and to finish at least six weeks before the first autumn rains, and for removing at least thirty centimetres below the internal limit of the discoloration.
- [11] UC IPM Pest Management Guidelines, Apricot. UC Statewide Integrated Pest Management Program. Full text. Source for the shallow irregular earwig feeding on the fruit surface, for its single generation a year with two nymph hatchings in late spring and early summer, for its nocturnal behaviour and monitoring with boards or rolled-up newspapers, for the brown apricot scale with one generation a year overwintering as a nymph, and for the five to ten generations of European red mite.
- [12] Bem F. (2007). The most serious virus diseases of apricot, peach and plum. Georgia – Ktinotrofia, issue 6/2007, in Greek. Full text. Source for the dominance of the PPV-M strain of Greek origin in Greece and its epidemic character with ready aphid transmission, and for yellow rings on the stone combined with chlorotic bands on the leaves as the diagnostic feature of sharka on apricot.
- [13] Damos P.T., Soulopoulou P., Gkouderis D., Monastiridis D., Vrettou M., Sakellariou D., Thomidis T. (2022). Degree-day risk thresholds for predicting the seasonal flight activity of stone fruit moth pests. Plant Protection Science. Full text. Source for the degree-day figures in orchards in Pella, first catch of peach twig borer at 70 and peak at 150.6 with a lower threshold of 11.4 °C, first catch of oriental fruit moth at 33 and peak at 77.9 with a lower threshold of 9.5 °C. The measurements were made in peach orchards of the same area and are transferred to apricot as the closest available Greek data, not as measurements in the crop.
- [14] Nasouri H. (2024). Capnodis tenebrionis (Coleoptera: Buprestidae). Journal of Integrated Pest Management 15(1):20. Peer-reviewed review. Source for egg laying starting at 23 °C with an optimum of 30 to 34 °C, for larval development of 6 to 18 months, and for egg laying in dry soil near the trunk.
- [15] Agricultural Warnings, Technical Bulletin for Apricot no. 1, 16 February 2026. Hellenic Ministry of Rural Development and Food, Regional Centre for Plant Protection, Quality and Phytosanitary Control of Thessaloniki, in Greek. Full text. Source for the description of shot hole symptoms on leaves, fruit and buds with the initially red lesions and the perforation of the blade, and for placing the intervention at stages A to B, just before bud swell, only in orchards with documented infections in the two preceding years.
- [16] Database of approved plant protection products. Hellenic Ministry of Rural Development and Food, in Greek. The only valid source for what is permitted in Greece today, by crop and by pest or disease. These approvals are valid in Greece only.
- [17] Luo C.-X., Schnabel G., Hu M., De Cal A. (2022). Global distribution and management of peach diseases. Phytopathology Research 4:30. Full text, peer-reviewed review. Source for the distribution of the Monilinia species and for the spread of M. fructicola.
- [18] Tree Fruit Insect Pest, Green Peach Aphid. Penn State Extension. Full text. Source for the overwintering of Myzus persicae under the bud scales and for the migration of winged forms during June and July.
- [19] Peach Twig Borer. UC Statewide Integrated Pest Management Program. Full text. Source for the overwintering of peach twig borer as a first or second instar larva in hibernacula in crotches and pruning wounds, and for the attack on shoots before fruit.
- [20] Pellizzari G., Duso C., Rainato A., Pozzebon A., Zanini G. (2012). Phenology, ethology and distribution of Pseudococcus comstocki, an invasive pest in northeastern Italy. Bulletin of Insectology. Full text. Source for the three generations a year, overwintering as an egg, hatching of the first generation in April on the leaves, and movement of females to the bark and the stem cavity of the fruit.
- [21] EPPO Global Database, Prunus sp. (PRNSS), pest list. Source for the record of Grapholita molesta as a pest of the genus Prunus, to which apricot belongs.
- Annual cultural operations for apricot, with the spray and fertilisation calendar
- Apricot cultivars, an evaluation, available in Greek only
- Bacterial canker on apricots and bacterial canker of stone fruit
- Scab on apricots
- Brown rot of stone fruit
- The flatheaded root borer and the goat moth
- Phytophthora and crown rots in fruit trees
- The Mediterranean fruit fly and the brown marmorated stink bug
- Beneficial insects, predatory mites and entomopathogenic nematodes
- Diseases and pests of peach and of almond, each with its own diagnostic tool
Plant protection products are used solely on the basis of the approvals of the Hellenic Ministry of Rural Development and Food and of the instructions on each product label [16]. Those approvals are valid in Greece only and do not apply in any other country. This article proposes no active substance and no application rate. The thresholds, temperatures and time windows cited are indicative, come from the literature listed, and do not constitute a recommendation to intervene.
Part of the data comes from Italian and American sources. The Italian ones concern Mediterranean conditions comparable to the Greek ones, though with a wetter spring in the Po valley, and the American ones concern a climate and a cultural practice that differ. Wherever no Greek datum was found, that is stated explicitly in the text.
In every case of foliar spraying on trees carrying fruit there is a risk of staining the fruit and scorching the foliage. A prior test on a limited number of trees is required, with the same product and the same rate, and a wait of five to seven days before general application. Spraying is done in the late afternoon or early morning, never in a heatwave and never on foliage under water stress.
The diagnostic tool is an aid to ranking probabilities and is not a diagnosis. Errors or omissions in the data of the tool itself cannot be excluded. For regulated harmful organisms, such as plum pox virus and the stone fruit phytoplasma, diagnosis and management rest solely with the competent phytosanitary authority.
Every intervention is made at the user's own responsibility and after an on-site assessment by a licensed agronomist. Pastopoulos Agronomics accepts no liability for the use of the information in this article.
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