Diagnosis

1.1. When to Start Diagnosing and How Often to Do It?

Diagnosis is not a one-time event, but a regular process. The earlier you notice a problem, the easier it will be to deal with.

• Scheduled Spring Inspection: Begin inspecting your trees in early spring, as soon as the snow melts and temperatures are consistently above freezing, before buds begin to swell. This is the time to assess winter damage to the bark (frost cracks, sunscald) and the condition of dormant buds.
• Regular Inspections Throughout the Season: From bud break until leaf fall, conduct inspections at least once every 1-2 weeks. Pay especially close attention to the garden during flowering and during the fruit growth period.
• Unscheduled Inspection: Conduct this after heavy rains, hail, storms, or sharp temperature fluctuations. Such events can trigger disease outbreaks.
• Autumn Inspection: After harvesting, but before leaf fall, carry out a final inspection to assess the tree's condition before winter and plan sanitation pruning work.

Why this works: Regular monitoring allows you to track dynamics. You will be able to distinguish an accidental defect from an emerging epiphytotic (mass spread of disease). Knowing the "norm" for your garden helps you spot deviations more quickly (Phillips, 2005).

1.2. Sequence of Inspection: From General to Specific

To avoid missing important details, inspect the tree using a single algorithm. Start with the general, then move to the specific.

1. General Inspection (from 3–5 metres): Step back a few steps from the tree and assess its overall habitus (appearance).

• Pay attention to the overall shape of the crown. Is there any asymmetry or one-sided drying of branches?
• Assess the colour and density of the foliage. Are there individual branches or entire sections that stand out from the general picture (e.g., have turned yellow or dried out)?
• Look for obvious damage, cracks, or growths on the bark of the trunk and main branches.

2. Inspection of the Root Zone and Root Collar:

• Examine the soil in the root zone. Are there signs of rodent activity (burrows, gnaw marks), accumulations of fine sawdust (a sign of root pests)?
• The root collar is the transition point between the trunk and the roots. This is a critically important area. Carefully rake away the soil at the base of the trunk. Inspect the bark for damage, signs of rot, or growths. Damage to the root collar often leads to tree death.

3. Inspection of Scaffold Branches and Trunk:

• Carefully inspect the bark. Look for cracks, swellings, peeling, areas with discolouration, wounds, and droplets of resin (especially common in stone fruits, but also occurs in apples).
• Pay attention to the crotches of scaffold branches. These are weak points where disease pathogens (e.g., Cytospora canker) and pests often settle.

4. Inspection of the Crown and Leaves:

• Inspect the upper and lower sides of the leaves. Many pests (e.g., aphids, mites) and pathogens (e.g., downy mildew) hide on the underside.
• For small pests like spider mites, use a magnifying glass or a white sheet of paper: shake a branch over the sheet – the tiny fallen dots will be clearly visible.
• Pull on a leaf. If it detaches easily, this could be a sign of certain diseases or root problems.

5. Inspection of Fruits:

• Inspect both growing and fallen fruits. Fallen fruit is a valuable source of information. Cut open suspicious apples to see internal damage (caterpillar tunnels, brown rot infection).
• Pay attention to the shape, colour, and presence of spots on the fruits.

1.3. What Signs to Look for First?

During the inspection, you will encounter a vast amount of visual information. To avoid confusion, note any deviations from the norm and group them by symptom type:

• Discolouration: Yellowing, browning, reddening, blackening, general paleness (chlorosis).
• Spotting: Spots can be of different colours, sizes, and shapes (round, angular). Assess their location on the leaf (edges, between veins, around veins) and structure (with or without coating, with or without a border).
• Coatings: Powdery, cobweb-like, sooty, mould-like.
• Deformations: Curling, wrinkling, blistering (galls), "witches' brooms", shoot distortion.
• Dieback (Necrosis): Death of individual parts (leaf tips, whole leaves, shoots, bark).
• Drop: Premature dropping of leaves, flowers, fruit sets, or fruits.
• Cracks and Bark Damage: Bark peeling, "swellings", presence of holes and tunnels under the bark, exudation of sap or gum.
• Presence of the Pathogens Themselves: The pests themselves (caterpillars, aphids, mites) or their traces (egg masses, webbing, excrement).

Important! Do not jump to conclusions. The same symptom can be caused by different reasons. For example, leaf curling can be a result of aphid activity, a symptom of potassium deficiency, or a reaction to drought. Only by gathering all the data and analysing it as a whole will you be able to make a correct "diagnosis" (Buckingham, 2010).

In the second chapter, we will look at how the localisation of the problem (leaves, shoots, roots) helps narrow down the list of "suspects" and begin accurate diagnosis.

2.1. Leaves

Leaves are the tree's "laboratory" where photosynthesis occurs. They are the first to react to most problems.

• What can you notice on the leaves?
• Colour change: Chlorosis (yellowing), reddening, appearance of a bronze tint.
• Spots: Of various colours, shapes, and sizes. They can be distinct or blurry, with or without a border, with or without a surface coating.
• Coatings: White powdery, greyish, black sooty.
• Deformations: Curling, crinkling, blisters (galls), wrinkling.
• Drying and dropping: Premature drying of edges or the entire leaf blade, early leaf fall.

• Possible Causes:
• Fungal Diseases: Scab, powdery mildew, rust, leaf spots (Filimonova, 2014; Jones & Aldwinckle, 2002). These pathogens most often leave characteristic spots and coatings.
• Pests: Aphids, mites, leafrollers, leaf-mining moths. Aphids and mites suck sap, causing deformation, yellowing, and gall formation (Phillips, 2005). Leafrollers and leaf-miners leave traces in the form of rolled, skeletonised leaves or winding "mines."
• Nutrient Deficiency: Lack of nitrogen, potassium, magnesium, iron, or manganese manifests as chlorosis, necrosis, colour changes, and deformations (Westwood, 1993; Neilsen, 2003). For example, interveinal chlorosis on young leaves often indicates iron deficiency (Phillips, 2005).
• Abiotic Factors: Drought, waterlogging, sunburn, frost, herbicide damage.

2.2. Shoots

Shoots are the "skeleton" of the crown, through which nutrients move. Their condition reflects the overall health of the tree.

• What can you notice on the shoots?
• Tip dieback: Death of the ends of annual or perennial branches.
• Distortions and deformations: Changes in shoot shape, appearance of "witches' brooms" (clusters of thin, abnormally short twigs).
• Coatings: Appearance of a white powdery coating on shoots (the overwintering stage of powdery mildew).
• Bark damage: Cracks, swellings, traces under the bark (pest tunnels).

• Possible Causes:
• Fungal and Bacterial Diseases: Monilial burn (brown rot), Cytospora canker, Nectria canker, fire blight (Erwinia amylovora) cause shoot dieback and blackening (Jones & Aldwinckle, 2002). Moniliosis often affects flowers and fruit spurs and then spreads to shoots.
• Pests: Clearwing moths, ambrosia beetles, and bark beetles bore tunnels under the bark, leading to branch dieback (Rieger, 2010). Caterpillars of some owlet moths and loopers can eat bark and buds on shoots (Phillips, 2005).
• Mechanical Damage: Breakage from wind, snow, or careless pruning opens the door to infections.

2.3. Bark and Trunk

Bark is the tree's "skin," protecting it from external influences. Damage to the trunk and main branches are the most dangerous signals.

• What can you notice on the bark?
• Cracks: Frost cracks, sunscald, tears from sharp temperature fluctuations (Jackson, 2003).
• Colour change: Darkening, reddening, areas of dead bark.
• Peeling and flaking: Bark falling off, exposing wood.
• Growths and cankers: Swellings, cancerous formations, gum exudation (especially in stone fruits, but occasionally in apples).
• Holes: Round or oval tunnels left by pests.
• Sunken areas: Cankers or "wounds" that may indicate fungal infections.

• Possible Causes:
• Fungal Diseases: Black rot (apple canker), European canker, Cytospora canker. These diseases cause deep cankers and bark dieback (Rieger, 2010; Buckingham, 2010).
• Pests: Bark beetles, ambrosia beetles, and rodents (mice, hares) that can gnaw the bark in winter (Phillips, 2005).
• Abiotic Factors: Frost cracks, sunscald (especially on the south side of the trunk), damage from agricultural machinery (Westwood, 1993).

2.4. Flowers and Fruit Sets

Flowers and fruit sets are the future harvest. Problems at this stage are critical because they directly affect yield.

• What can you notice?
• Wilting and blackening: Sudden wilting, blackening, and drying of flowers and young fruit sets.
• Drop: Massive dropping of flowers and fruit sets without obvious external damage.
• Deformations: Improper development of flowers, change in their shape.

• Possible Causes:
• Diseases: Monilial burn (flowers and fruit sets turn brown, dry up, and often remain hanging on the tree – a distinguishing feature). Fire blight also causes blackening and drying of inflorescences (Rieger, 2010; Jones & Aldwinckle, 2002).
• Pests: Apple blossom weevil – a beetle that eats stamens and pistils inside buds. Fruit sets can be damaged by codling moth larvae.
• Abiotic Factors: Frost during flowering is the most common cause of fruit set drop. Dry, windy weather can also hinder pollination.
• Nutrient Deficiency: Boron and calcium deficiencies can cause fruit set drop and fruit deformation (Westwood, 1993; Neilsen, 2003).

2.5. Fruits

Apples are the result of all the tree's work. Damage to the fruits makes the harvest unsuitable.

• What can you notice on the fruits?
• Spots and rot: Appearance of spots of various colours, soft areas, rot (dry or wet).
• Deformations: Ugly shape, distortions.
• Tunnels and damage: Punctures, tunnels under the skin, presence of larvae or their excrement.
• Cracks: Cracking of the fruit skin.

• Possible Causes:
• Fungal Diseases: Scab, brown rot (moniliosis), sooty mould, powdery mildew. All leave characteristic spots, coatings, or rot (Buckingham, 2010; Rieger, 2010).
• Pests: Codling moth, apple maggot, weevils. Their larvae bore tunnels inside the fruits (Phillips, 2005).
• Physiological Disorders: Bitter pit (calcium deficiency), fruit sunburn, water core (metabolic disorder) (Westwood, 1993; Jackson, 2003).

2.6. Roots

Roots are the "underground" part of the tree that we rarely see. But they provide water and nutrition.

• How to identify root problems? Root problems often manifest in the above-ground parts, but have their own characteristics.
• Signs: General growth depression, small and pale leaves, premature leaf fall, branch dieback, but without clear local lesions (no spots, coatings, etc.). The tree simply "wastes away" for no apparent reason.
• Upon digging up the soil (as a last resort), you may see rotten, dark roots with an unpleasant odour.

• Possible Causes:
• Fungal Diseases: Root rots (Phytophthora, Armillaria, Verticillium wilt). Pathogens live in the soil and infect the root system (Rieger, 2010).
• Pests: Larvae of the cockchafer (May beetle), wireworms, root aphids can damage roots (Phillips, 2005).
• Abiotic Factors: Flooding, soil compaction, lack or excess of moisture, and "soil fatigue" – accumulation of toxic substances in the soil (Westwood, 1993).

Remember: Localisation of the problem is your "compass" in the world of diagnosis. If you see yellowing on old leaves at the bottom of the crown, it is highly likely a nutrient deficiency. If you notice a white coating on young leaves and shoots, it is powdery mildew. If the bark on the trunk has darkened and is covered with cankers, it is most likely a fungal disease threatening the tree's life.

In the next chapter, we will analyse in detail how to determine the specific cause of a problem based on the appearance of symptoms (discolouration, deformation, coating, etc.).

3.1. Discolouration

Apple tree leaves and bark change colour, signalling various problems.

Yellowing (Chlorosis):

• What it looks like: Leaves become pale green, yellow, sometimes almost white. Veins may remain green (in the case of iron or manganese deficiency) or turn yellow along with the leaf.
• Possible Causes:
• Nutrient deficiency: Nitrogen deficiency causes general yellowing of old leaves (Neilsen, 2003; Westwood, 1993). Iron deficiency (iron chlorosis) manifests as yellowing between the veins of young leaves, while the veins themselves remain green. Magnesium and potassium deficiencies also cause characteristic colour changes (Phillips, 2005).
• Waterlogging or drought: With excess moisture, roots suffer from lack of oxygen, which prevents nutrient uptake, and leaves turn yellow. In drought, the plant cannot obtain sufficient water and nutrients (Westwood, 1993).
• Pests: Aphids and mites, by sucking sap, cause yellowing and curling of leaves (Buckingham, 2010).
• Diseases: Some viral and fungal diseases, such as mosaic and chlorosis, are also accompanied by leaf colour changes (Jones & Aldwinckle, 2002).

Reddening or Browning of Leaves:

• What it looks like: Leaves take on a red, bronze, or brown tint. This often starts at the edges or between the veins.
• Possible Causes:
• Phosphorus or potassium deficiency: With phosphorus deficiency, leaves may darken and take on a purplish hue. Potassium deficiency manifests as browning and drying of leaf edges (marginal scorch) (Westwood, 1993).
• Frost damage: Early autumn or late spring frosts can cause reddening and browning of tissues (Jackson, 2003).
• Drought or overheating: In hot, dry weather, leaves may "burn" at the edges, becoming brown and brittle (Phillips, 2005).

3.2. Spotting

Spots on leaves, fruits, and bark are one of the most informative symptoms.

Types of spots: Round, angular, diffuse, clearly outlined. Size ranges from small dots to large spots. Colour: brown, black, dark brown, grey, with or without a border.

Possible Causes:

• Fungal Diseases:
• Scab (Venturia inaequalis): Olive-brown, velvety spots appear on leaves, later turning black. On fruits, dark, cracked spots appear (Buckingham, 2010; Rieger, 2010).
• Rust (Gymnosporangium spp.): Orange or rusty spots with dark dots in the centre appear on the upper side of leaves (Jones & Aldwinckle, 2002).
• Leaf spots (Filimonova, 2014): Various fungi cause leaf spots with clear boundaries, e.g., brown or grey spot, often with a characteristic border.
• Black rot (Apple canker) (Sphaeropsis malorum): Sunken brown or black cankers appear on the bark, small purple spots on leaves, and dark spots on fruits (Buckingham, 2010).
• Bacterial Diseases:
• Fire blight (Erwinia amylovora): Watery, darkening spots appear on leaves, spreading along the veins (Jones & Aldwinckle, 2002).
• Physiological Disorders:
• Bitter pit (calcium deficiency): Sunken, brown spots form on fruits, especially at the calyx end (Westwood, 1993; Jackson, 2003).

3.3. Coatings and Exudations

Coatings are often fungal spores or pest waste products.

White Powdery Coating:

• What it looks like: Resembles sprinkled flour, easily wiped off. Affects leaves, shoots, flowers, and fruit sets.
• Cause: Powdery mildew (Podosphaera leucotricha) – a fungal disease especially active in dry, warm weather (Buckingham, 2010; Rieger, 2010).

Black Sooty Coating:

• What it looks like: Black, velvety, resembling soot. Often appears on leaves and fruits.
• Cause: Sooty mould (Capnodium spp.). It does not parasitise the plant but develops on the sugary secretions (honeydew) of aphids and other sap-sucking pests. It is not dangerous in itself but indicates the presence of pests and shades leaves, disrupting photosynthesis (Phillips, 2005).

Gum (Resinous Exudation):

• What it looks like: Sticky amber or brown liquid exuding from cracks and wounds on the bark.
• Cause: This is the tree's protective reaction to damage. Gummosis often accompanies fungal bark diseases (Cytospora canker, black rot), pest damage (bark beetles, ambrosia beetles), and mechanical injuries (Filimonova, 2014; Rieger, 2010).

3.4. Deformations

Changes in the shape of leaves, shoots, or fruits.

Leaf Curling:

• What it looks like: Leaves roll into a tube or boat shape, become crinkled.
• Possible Causes:
• Aphids: Sucking insects extract sap, causing leaf deformation (Buckingham, 2010).
• Potassium deficiency: Leaf edges and tips curl upwards (Westwood, 1993).
• Powdery mildew: Young leaves become narrow, curled, and brittle (Rieger, 2010).

Shoot Distortion, "Witches' Brooms":

• What it looks like: Shoots grow abnormally, with short internodes, forming dense, abnormal clusters of branches.
• Cause: Often caused by microorganisms, e.g., viruses or some fungi. Can also be a reaction to tissue damage by pests (Jackson, 2003).

Fruit Deformation:

• What it looks like: Apples become ugly, with bumps, dents, irregular shapes.
• Possible Causes:
• Pests: Aphids and codling moths can cause deformations (Buckingham, 2010).
• Boron deficiency: Fruits may have deformations and corky growths (Neilsen, 2003).
• Scab: Severe scab infection makes fruits small and deformed (Rieger, 2010).

3.5. Dieback and Drop

Premature wilting, drying, and dropping of plant parts.

Shoot Dieback (Dieback):

• What it looks like: Death of shoot tips, starting from the ends. Bark on dried areas may darken.
• Possible Causes:
• Fungal Diseases: Moniliosis, Cytospora canker, Nectria canker (Filimonova, 2014). In moniliosis, branches look "scorched."
• Fire blight: Shoot tips wilt, blacken, and bend into a "shepherd's crook" shape (Jones & Aldwinckle, 2002).
• Pests: Clearwing moths and bark beetles, by boring tunnels, disrupt sap flow, leading to branch dieback (Phillips, 2005).

Premature Dropping of Leaves, Flowers, and Fruits:

• What it looks like: Leaves turn yellow and fall prematurely, flowers and fruit sets drop en masse, fruits fall immature.
• Possible Causes:
• Natural process: Some dropping of fruit sets ("June drop") is normal, as the tree regulates its load (Phillips, 2005).
• Drought or waterlogging: Stress causes protective shedding of parts.
• Diseases: Scab can cause early leaf fall. Moniliosis causes fruit drop.
• Pests: Codling moth, apple maggot, and blossom weevil lead to fruit drop (Buckingham, 2010).

3.6. Cracks and Bark Damage

Breaches in the bark integrity are open doors for infections and a sign of serious problems.

Cracks (Frost Cracks):

• What it looks like: Vertical, often deep cracks on the trunk, running along the bark.
• Cause: Sharp temperature fluctuations in winter, especially after thaws. Sunscald on the south side of the trunk (Jackson, 2003; Phillips, 2005).

Peeling and Flaking Bark:

• What it looks like: Bark swells, cracks, and separates from the wood.
• Possible Causes:
• Fungal Diseases: Black rot and European canker cause necrosis and bark peeling with canker formation (Rieger, 2010).
• Pests: Activity of bark-boring pests also leads to bark peeling.

3.7. Presence of the Pathogens Themselves

Sometimes symptoms are not just consequences but also the causes themselves, visible to the naked eye.

Pests:

• What they look like: Aphids – small green or black insects on young shoots. Mites – reddish dots on the underside of leaves. Codling moth caterpillars – in tunnels inside apples (Phillips, 2005).

Spores and Fruiting Bodies of Fungi:

• What they look like: Swellings on leaves (rust), black dots in the centre of spots (leaf blotch), bracket fungi on the trunk (polypores).

Remember the main point: Carefully inspect all parts of the tree. Often, one symptom does not give the full picture. Combine localisation (Chapter 2) and symptoms (this chapter) to narrow down the possible causes. In the next chapter, we will bring everything together and examine specific causes: diseases, pests, nutritional disorders, and care mistakes.

4.1. Diseases (Infectious Diseases)

This is the largest and most dangerous group of causes. Pathogens can be fungi, bacteria, or viruses. It is important to understand that most fungal diseases develop in conditions of high humidity and warmth (Filimonova, 2014; Jones & Aldwinckle, 2002).

Fungal Diseases:

• Scab (Venturia inaequalis): One of the most common diseases. Affects leaves, fruits, and sometimes young shoots.
• Symptoms: On leaves – olive-brown, velvety spots that later turn black. On fruits – dark, cracked, corky spots. Severe infection leads to fruit deformation and early leaf fall (Buckingham, 2010; Rieger, 2010).
• Development conditions: Cool, wet spring. The fungus overwinters on fallen leaves, so autumn leaf collection is an important preventive measure (Phillips, 2005).
• Powdery Mildew (Podosphaera leucotricha): Affects all young, actively growing tissues: leaves, shoots, buds, fruit sets.
• Symptoms: White powdery coating on leaves and shoots. Affected leaves curl, become brittle, and shoots stop growing. Fruits become covered with net-like russeting (Buckingham, 2010; Rieger, 2010).
• Development conditions: Unlike scab, powdery mildew prefers dry, warm weather. The fungus overwinters in buds, so control begins in early spring (Phillips, 2005).
• Moniliosis (Brown Rot) (Monilinia fructigena): A dangerous disease affecting fruits and shoots. It occurs in two forms: fruit rot and monilial burn.
• Symptoms: Fruit rot appears on ripening fruits – brown rot spots with white or cream-coloured spore cushions appear. Monilial burn affects flowers, fruit sets, and young twigs – they wilt, turn brown, and dry up, but often remain hanging on the tree (Phillips, 2005; Rieger, 2010).
• Development conditions: Wet, warm weather. Overwinters in mummified fruits and infected bark (Buckingham, 2010).
• Rust (Gymnosporangium spp.): A disease that requires two hosts for its development: apple and juniper.
• Symptoms: Bright orange or rusty spots appear on the upper side of leaves. On the underside, growths with tubes from which spores are released (Jones & Aldwinckle, 2002; Buckingham, 2010).
• Development conditions: Warm, wet spring. If there are junipers near the orchard, the risk of infection increases significantly (Phillips, 2005).
• Black Rot (Apple Canker) (Sphaeropsis malorum): A dangerous fungal disease affecting bark, branches, leaves, and fruits. Can lead to tree death.
• Symptoms: Sunken brown or black cankers appear on the bark, which gradually enlarge. Bark on affected areas peels off. Brown or purple spots on leaves, black rot spots on fruits (Buckingham, 2010).
• Development conditions: The fungus enters the tree through wounds in the bark, so protection against frost cracks and injuries is very important (Rieger, 2010).
• Cytospora Canker (Cytospora spp.) and European Canker (Nectria galligena): Fungal diseases causing branch dieback and bark wound formation. Often develop on weakened trees (Filimonova, 2014; Rieger, 2010).

Bacterial Diseases:

• Fire Blight (Erwinia amylovora): One of the most dangerous quarantine diseases that can quickly destroy an entire orchard.
• Symptoms: Affects flowers, shoots, branches. Flowers and young leaves suddenly wilt, blacken, and dry up. Shoots bend, taking on a characteristic "shepherd's crook" shape. Droplets of cloudy liquid (bacterial exudate) may appear on infected bark (Jones & Aldwinckle, 2002; Rieger, 2010).
• Characteristics: The disease spreads with rain, wind, and insects. Treatment is difficult, especially in later stages (Phillips, 2005).

Viral Diseases:

• Symptoms: Viruses often manifest as mosaic leaf colouration (alternating green and yellow areas), deformation, stunting, bark dieback (Jackson, 2003). A characteristic sign of many viruses is "witches' brooms" (clusters of ugly shoots).
• Characteristics: Viruses are incurable. They spread with the sap of infected plants (e.g., through tools) and sap-sucking insects (aphids, leafhoppers) (Jones & Aldwinckle, 2002). Therefore, the main control is prevention and removal of infected trees.

4.2. Pests (Insects and Their Larvae)

Pests cause harm both by directly damaging tissues and indirectly by transmitting diseases.

Sap-Sucking Pests (Aphids, Mites, Psyllids):

• How they cause harm: They pierce tissues with their mouthparts and suck out sap, weakening the plant. They also excrete sweet honeydew, on which sooty mould develops (Phillips, 2005).
• Symptoms: Leaf curling and yellowing, sticky coating, sooty mould, webbing (mites). Young shoots become deformed, trees are stunted (Buckingham, 2010).

Leaf-Chewing Pests (Caterpillars, Sawfly Larvae):

• How they cause harm: They eat leaves, buds, flowers. In mass outbreaks, they can completely defoliate the tree.
• Symptoms: Chewed leaves with holes, skeletonised leaves (only veins remain), eaten buds and flower buds. For example, winter moth eats leaves in early spring (Phillips, 2005).

Fruit Pests (Codling Moth, Apple Maggot, Weevils):

• How they cause harm: Larvae penetrate inside fruits, eating the flesh and seeds. This is the most direct threat to the harvest.
• Symptoms: Tunnels inside fruits, presence of excrement ("worm holes"), premature drop and rotting of apples. Apple blossom weevil damages flower buds from the inside (Buckingham, 2010).

Bark and Wood Pests (Bark Beetles, Ambrosia Beetles, Clearwing Moths):

• How they cause harm: They bore tunnels under the bark and in the wood, disrupting sap flow. This can lead to the death of large branches and the entire tree.
• Symptoms: Oval or round holes on the bark, sawdust ("frass"), wilting and dieback of branches. Presence of long winding tunnels with larvae under the bark (Phillips, 2005; Rieger, 2010).

Rodents (Mice, Hares):

• How they cause harm: In winter, they gnaw the bark on the trunk and lower scaffold branches.
• Symptoms: Characteristic gnaw marks on the bark, often ring-shaped. Ring barking leads to tree death (Phillips, 2005).

4.3. Mineral Nutrition Disorders

Like any plant, the apple tree needs balanced nutrition for normal functioning. Deficiency or excess of elements causes characteristic symptoms (Westwood, 1993; Neilsen, 2003).

Nitrogen (N):

• Deficiency symptoms: Leaves are pale green, small. Shoot growth is weak. Old leaves turn yellow and fall prematurely (Westwood, 1993).
• Excess symptoms: Vigorous shoot growth at the expense of fruiting. The tree becomes "over-vigorous," reducing frost hardiness and disease resistance (Phillips, 2005).

Potassium (K):

• Deficiency symptoms: Yellowing and browning of leaf edges (marginal scorch). Leaves may curl upwards. Fruits become smaller, their colour fades (Buckingham, 2010; Westwood, 1993).

Phosphorus (P):

• Deficiency symptoms: Leaves become dark green or take on a bronze-purple tint. Growth slows, flowering and fruiting are weaker (Neilsen, 2003).

Iron (Fe) and Manganese (Mn):

• Deficiency symptoms (chlorosis): Yellowing between the veins appears on young leaves, while the veins themselves remain green. This is a common problem on calcareous (alkaline) soils (Phillips, 2005; Neilsen, 2003).

Calcium (Ca):

• Deficiency symptoms: "Bitter pit" – dark, sunken spots appear on fruits. Dieback of terminal buds and young leaves may also occur (Jackson, 2003).

Boron (B):

• Deficiency symptoms: Dropping of fruit sets, fruit deformation (with corky growths), dieback of shoot tips (Westwood, 1993).

4.4. Unfavourable Weather Conditions (Abiotic Factors)

Nature is not always on our side. Weather stress can weaken the tree and make it easy prey for diseases and pests.

Frost Cracks:

• What they look like: Vertical cracks and bark peeling on the trunk. Often appear on the south and south-west sides, where temperature fluctuations are sharpest (Jackson, 2003; Phillips, 2005).

Sunscald:

• What it looks like: Darkening and death of bark, especially on the south side of the trunk in late winter – early spring.

Drought and Overheating:

• Symptoms: Leaves wilt, turn yellow, curl, edges dry. Fruits may get sunburned, developing dark spots. During prolonged drought, leaf drop begins (Westwood, 1993).

Waterlogging and Stagnant Water:

• Symptoms: Leaves turn yellow, often for no apparent reason. The root system suffocates without oxygen, leading to root rot. The tree weakens and may die (Phillips, 2005).

4.5. Care Mistakes

Unfortunately, incorrect actions by the gardener can themselves become a cause of problems.

• Improper pruning: Too severe pruning weakens the tree, causing excessive growth of "water sprouts." Leaving stubs and bark tears is an open door for infections (Filimonova, 2014).
• Improper planting: Burying the root collar or planting in poorly drained soil leads to stress and tree death (Phillips, 2005).
• Unbalanced fertilisation: Excess nitrogen makes the tree "over-vigorous" and vulnerable to diseases. Potassium and micronutrient deficiencies lead to physiological disorders (Westwood, 1993).
• Bark damage: Wounds from mowers, garden tools, wire girdling – all are entry points for diseases.
• Untimely cleaning: Leaving fallen leaves and mummified fruits over winter is a breeding ground for infection (Buckingham, 2010).

Important note: Problems often arise not from one cause but from several simultaneously. For example, a tree weakened by drought may be attacked by bark beetles and then infected with Cytospora canker. Therefore, when making a diagnosis, always assess the tree's condition comprehensively. In the next chapter, we will look at situations requiring urgent intervention to save the tree.

5.1. Rapid Spread of Symptoms

If you notice that the problem is spreading at an alarming rate, it is a sure sign that you are dealing with a dangerous disease or pest.

What you see:

• Spots on leaves that increase in size within days, or new spots appear.
• Dieback and blackening of shoots spreading through the crown, moving from annual twigs to perennial branches.
• Massive yellowing and leaf drop over a short period (3-5 days).
• Rapid enlargement of cankers on the bark, appearance of large amounts of exudate (gum).
• A sharp increase in pest numbers (e.g., appearance of whole aphid colonies on several branches in a single day).

What to do:

• Urgently conduct a re-inspection and clarify the diagnosis. If you are unsure of the cause, take photos and consult a specialist (agronomist, regional plant protection centre).
• Begin treatment immediately once the diagnosis is established. Use systemic products that penetrate plant tissues quickly.
• Remove and burn affected organs (branches, leaves, fruits) to stop the spread of infection or pests (Buckingham, 2010).
• Why this is important: Many pathogens (e.g., Erwinia amylovora – the causal agent of fire blight) can destroy a tree in a single season. Diseases spreading through the vascular system, such as Verticillium wilt or root rots, quickly block the movement of water and nutrients (Jones & Aldwinckle, 2002).

5.2. Damage to the Trunk and Root Collar

The trunk and root collar are the tree's "mainline." Damage in this area is the most dangerous because it disrupts the connection between roots and crown.

Situations Requiring Urgent Intervention:

• Ring barking: If the bark is damaged around the entire circumference of the trunk, sap flow stops and the tree is doomed. Causes: rodents (hares, mice), frost cracks, sunscald (Phillips, 2005).
• Deep cracks and cankers on the trunk: Cracks that penetrate deep into the wood, especially if they appear at old wound sites. These are entry points for dangerous fungal diseases (black rot, bracket fungi) (Rieger, 2010).
• Presence of bracket fungus fruiting bodies: Appearance of growths (bracket fungi) on the trunk means the fungus is actively destroying the wood from the inside. This is a very serious signal.
• Excessive gum exudation on the trunk: In apples, gummosis can indicate deep damage and be a sign of dangerous diseases (Filimonova, 2014).

What to do:

• Clean the wound down to healthy wood (using a knife, chisel). Remove all dead and damaged bark.
• Treat the wound with a 1-3% solution of copper sulfate or another permitted fungicide.
• Cover the wound with grafting wax, a special paste, or oil paint on natural drying oil to protect it from infection.
• In case of ring barking: If the damage is partial, clean the wound edges and the tree may recover. With complete ring barking on an adult tree, chances are slim. A young tree can be attempted to be saved by bridge grafting (Phillips, 2005). In spring, when sap flow begins, take several cuttings from last year's shoots and graft them across the damaged area of the trunk, connecting the bark above and below the wound.

5.3. Massive Branch Dieback (Crown Dieback)

Dieback of large branches or a significant part of the crown is always an alarming signal. If the problem affects more than 30% of the crown, the tree is in critical condition.

Signs:

• Dieback of entire scaffold branches, starting from the tips.
• Blackening and peeling of bark on dying branches.
• Leaves on affected branches turn yellow, dry up, and do not fall, remaining hanging dry.

Possible Causes:

• Fungal diseases (Cytospora canker, black rot, European canker).
• Fire blight (especially if dieback starts with flowers and spreads rapidly).
• Pest activity (bark beetles, ambrosia beetles, clearwing moths) (Phillips, 2005).
• Root rots or root damage.
• Severe drought (if signs of dieback appeared during hot weather).

What to do:

• Urgently determine the cause. Inspect the bark for holes, tunnels under the bark, signs of disease.
• Immediately remove all dead and dying branches. Make cuts 10-15 cm below the boundary between healthy and diseased wood (Jones & Aldwinckle, 2002). Burn all cut material outside the site.
• Apply a systemic fungicide or insecticide (depending on the cause). It is important to use a product that penetrates plant tissues and fights the pathogen from within.
• Why this is important: Dieback of large branches means the problem has already penetrated deep into the wood. Delay will lead to the death of the entire tree, as the pathogen or pest will continue to spread through the vascular system.

5.4. Signs of Tree Death

This is the most difficult situation. Sometimes symptoms indicate that the tree cannot be saved.

Signs of Irreversibility:

• Complete ring barking of the trunk: If the bark is destroyed around the entire circumference at a height of more than 10-15 cm from the root collar, restoration of sap flow is impossible (Phillips, 2005).
• Massive bark dieback on the trunk: More than 70-80% of the bark on the trunk and main scaffold branches is damaged or peeled off.
• Presence of bracket fungi and obvious wood destruction: Wood becomes spongy, crumbles easily.
• Lack of growth and "bare" crown: The tree produces no new shoots, leaves are small, sparse, pale.
• Abundant root suckers: Sensing its demise, the tree makes a desperate attempt to survive by sending up shoots from the roots. But this does not save the tree itself.

What to do:

• Make a decision to remove the tree. If signs of irreversibility are obvious, the best thing you can do is cut down and uproot the tree to prevent it from becoming a source of infection for healthy neighbours.
• Treat the soil after removing the diseased tree, especially if the cause was root rots or pathogens capable of persisting in the soil for a long time. It is not recommended to plant new apple trees in this spot for the next 3-5 years (Rieger, 2010).

5.5. When Not to Panic

It is important to distinguish critical situations from normal seasonal phenomena or minor problems.

Do not panic if:

• You notice single leaves with small spots in late summer. This may be natural senescence or mild disease development.
• You observe natural "June" drop of fruit sets. The tree is regulating its load (Phillips, 2005).
• You find small cracks on old bark that are not deepening or enlarging.
• There is a small number of aphids on young shoots. They may be eaten by ladybirds and other natural enemies if you do not use insecticides.

Golden rule: If you are unsure about the severity of the problem, take a photo, show it to a specialist, or send it to a regional plant protection centre for diagnosis clarification. Better to be overcautious and start treatment early than to be too late.

Concluding Word

Diagnosing apple tree problems is a skill that comes with experience. I hope this article will help you become an attentive and caring "doctor" for your trees. Remember that healthy, strong trees resist diseases and pests better. Therefore, the most reliable way to protect your orchard is to provide your plants with proper care, timely watering, balanced fertilisation, and regular preventive inspections.

Wishing you strong trees and bountiful harvests!