Physiological disorders

Last updated: July 16, 2026 Español Русский

1. What Are Physiological Disorders?

Imagine this: your apple tree looks sick — leaves are yellowing, fruit is covered in spots, but you see no pests and find no fungus. Sound familiar? Chances are, you are dealing with a physiological disorder.

Physiological disorders are non-infectious injuries caused by adverse environmental conditions, improper care, or nutritional imbalances. Unlike diseases, they are not caused by pathogens (fungi, bacteria, viruses) but by stress factors: drought, waterlogging, nutrient deficiency or excess, frost, heat, and sunburn (Agustí, 2010; Westwood, 1993).

How to Tell Them Apart from Infectious Diseases?

This is a key skill for any gardener. Here are the main differences:

Feature	Physiological Disorders	Infectious Diseases
Spread	Do not spread to neighbouring trees	Spread from plant to plant
Localisation	Often symmetrical, affecting specific zones (e.g., the southern side of the trunk)	Random spots of various shapes and sizes
Weather link	Clearly linked to weather anomalies or care mistakes	May develop regardless of weather
Progression	May weaken when the cause is removed	Usually progress regardless of conditions

Important: physiological disorders weaken the tree and make it more vulnerable to infections. Therefore, timely identification and elimination of the cause is a form of disease prevention (Agustí, 2010).

Why Do They Occur?

The main causes of physiological disorders (Ferree & Warrington, 2003; Jackson, 2003):

1. Water regime disturbances — drought, waterlogging, sharp fluctuations in moisture

2. Nutritional imbalances — deficiency or excess of macro- and microelements

3. Unfavourable temperatures — frosts, thaws, heat

4. Sunburn — especially on the southern side of the trunk and on fruit

5. Poor cultivation practices — incorrect pruning, crop overload, root damage

Reversibility of Changes

This is a crucial practical question. Unlike infectious diseases, physiological disorders are often reversible — but not always:

Reversible: wilting from drought, chlorosis due to iron deficiency, small fruit from crop overload. When the cause is removed, the tree recovers.
Irreversible: frost cracks, bark death, watercore with tissue damage. Here, you can only help the tree heal its wounds.

Remember: the earlier you notice a problem, the higher the chance of fully restoring the tree's health.

2. Water-Related Disorders

Water is the foundation of life for an apple tree. But too much or too little can cause serious damage, and the symptoms are often mistaken for diseases. Let’s look at three main water-related scenarios.

2.1. Drought: When Water Is Scarce

The apple tree is a moderately moisture-loving crop. An adult tree consumes about 500–600 mm of rainfall or irrigation water per season (Rieger, 2010). In arid regions without irrigation, trees suffer, and this shows in characteristic signs.

How to recognise drought (Westwood, 1993; Trunov, 2012):

Leaves become pale green, yellow, and curl at the edges, especially on young shoots.
In severe drought, leaves drop prematurely — starting with the lower, older ones.
Shoots are weak and short (less than 20–25 cm), wood does not ripen before winter.
Fruit become smaller, lose juiciness, and may drop early.
On the sun-exposed side of fruit, sunken brown spots appear — sunburn is exacerbated by dehydration.

Why this happens. Apple roots are concentrated in the topsoil (up to 60–80 cm). When this layer dries out, the absorbing rootlets die, and the remaining roots cannot supply the tree with enough moisture. Photosynthesis is impaired, nutrient transport slows, and the formation of flower buds for the next year’s crop suffers (Westwood, 1993; Krivko, 2014).

What to do:

Water regularly, especially during critical phases: flowering, 6–7 weeks after bud break (fruit growth period), and 4–8 weeks before harvest (fruit filling) (Mandal et al., 2021).
Irrigation rate: for young orchards — 30–40 L per tree per watering into the trunk circle; for bearing trees — 50–60 L per 1 m² of crown projection (Krivko, 2014). Water less often but deeply, wetting the soil to a depth of 50–70 cm.
Mulch the trunk circle with a layer of 8–10 cm (peat, compost, mown grass, straw). Mulch retains moisture, prevents soil overheating, and suppresses weeds (Ferree & Warrington, 2003).
In regions with hot summers, consider drip irrigation — it delivers water directly to the roots, saving resources and avoiding over‑humidifying the air.

Important: drying out of the soil in late summer – early autumn (August–September) can even be beneficial: it slows shoot growth and promotes wood ripening, increasing winter hardiness. But during active fruit growth and flower bud formation, water shortage is unacceptable (Westwood, 1993; Trunov, 2012).

2.2. Waterlogging: When There Is Too Much Water

Excess water is no less dangerous than drought. Stagnant moisture in the root zone displaces oxygen; roots begin to suffocate and die.

Symptoms of waterlogging (Agustí, 2010; Krivko, 2014):

Leaves turn yellow (chlorosis) evenly over the whole tree, without the typical interveinal yellowing seen in iron deficiency.
Growth is stunted, shoots are thin and short.
Stone fruit neighbours may show gummosis; in apple, the bark at the root collar darkens, cracks, and may rot.
With prolonged flooding, leaves wilt, dry up and drop; the tree may die.

Causes. The apple tree does not tolerate groundwater levels above 1.5–2 m (Westwood, 1993). On heavy clay soils, even short-term flooding (more than 2–3 days) during the growing season causes irreversible damage to absorbing roots. Roots deprived of oxygen switch to anaerobic respiration, accumulate toxic substances (ethanol, acetaldehyde), leading to cell death (Westwood, 1993).

What to do:

Choose a site with deep groundwater (at least 2–2.5 m) and good drainage. On heavy soils, install drainage ditches before planting or plant trees on raised mounds 30–50 cm high.
Prevent flooding during snowmelt — divert water with small channels.
Loosen the soil after rains to restore aeration. Sowing green manures between rows helps structure the soil and improve gas exchange (Krivko, 2014).
If the site is periodically flooded, use rootstocks with higher tolerance to waterlogging (e.g., seedling rootstocks or MM.106) (Ferree & Warrington, 2003).

2.3. Water Balance Disruption: Sharp Fluctuations

Sharp changes in moisture — when a long drought is followed by heavy rain or intensive irrigation — are especially dangerous for apple trees.

Consequences of sharp fluctuations (Jackson, 2003; Westwood, 1993):

Fruit cracking. The skin cannot stretch fast enough to keep up with the rapidly expanding flesh — cracks appear, allowing fungal spores to enter. Thin-skinned varieties ('Golden Delicious', 'Cox Orange Pippin') are particularly prone.
Drop of fruit set and young fruit. When water suddenly becomes abundant, the tree channels resources into shoot growth at the expense of fruit, and young fruit drop en masse ('June drop' intensifies) (Krivko, 2014).
Watercore (glassiness) of fruit — the flesh becomes translucent, watery, especially near the stalk. This is a precursor to rapid spoilage in storage.
Bark damage — with sharp moisture fluctuations, bark may crack (especially on the trunk), opening the door to infections.

What to do:

Water evenly. Use drip irrigation or furrow irrigation with gradual wetting, avoiding flooding.
In dry periods, water every 7–10 days rather than infrequently and heavily — this reduces stress from fluctuations.
Mulching helps smooth out moisture fluctuations in the topsoil.
For varieties prone to cracking, calcium foliar feeds (calcium nitrate or calcium chloride) are beneficial — they strengthen cell walls in the skin (Neilsen & Neilsen, 2003; Ferree & Warrington, 2003).

Practical Summary: How to Avoid Water-Related Disorders

Situation	Your Actions
Arid region	Drip irrigation, mulching, watering at critical phases (flowering, fruit growth)
Heavy clay soil	Drainage, planting on mounds, loosening, choosing tolerant rootstocks
Sharp moisture fluctuations	Even watering, mulch, calcium foliar feeds
Spring water stagnation	Divert meltwater, plant on elevated sites

Remember: apple roots are especially sensitive to oxygen deficiency. Optimal soil moisture is 75–80% of field capacity. A simple test: take a handful of soil from 20–30 cm depth — if it does not crumble and does not run through your fingers, moisture is close to ideal (Trunov, 2012).

3. Nutritional Disorders

Apple nutrition is a complex mechanism. Deficiency, excess, or imbalance of nutrients shows up in characteristic symptoms that you need to be able to distinguish from diseases and injuries. This chapter will help you 'read' the signals the tree sends and adjust care in time.

Why Apple Trees Suffer from Nutritional Disorders

For normal growth and fruiting, an apple tree needs 16 elements. The main 'building' elements are nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur. Micronutrients — iron, manganese, zinc, boron, copper, molybdenum, and others — are needed in smaller amounts, but their deficiency or excess also affects tree health (Neilsen & Neilsen, 2003).

Causes of nutritional disorders are most often related not to the absence of an element in the soil, but to its unavailability: unsuitable pH, waterlogging, drought, soil compaction, or antagonism between elements (Westwood, 1993).

The gardener's golden rule: first check the conditions, then adjust nutrition. It is useless to apply fertiliser if the roots cannot absorb it because of waterlogging or drought.

3.1. Nutrient Deficiencies: How to Recognise and What to Do

Starvation symptoms appear on leaves, shoots, and fruit. It is important to distinguish them.

Nitrogen (N) — the basis of growth

Deficiency symptoms (Neilsen & Neilsen, 2003; Trunov, 2012):

Leaves are pale green, uniformly yellowing — starting with the older, lower leaves.
Shoots are short, thin, with reddish-brown bark.
Fruit are small, pale-coloured, drop early.
Flowering is weak, fruit set is poor.

What to do:

Apply nitrogen fertilisers in spring, at the start of shoot growth — urea, ammonium nitrate, or ammonium sulfate (Ferree & Warrington, 2003).
Rate: 30–60 kg/ha of active ingredient for mature orchards; per tree — about 100–150 g of urea worked into the trunk circle (Krivko, 2014).
For a quick effect, use foliar feeding with urea (0.5–1% solution) — it is absorbed by leaves within 2–3 hours (Mandal et al., 2021).

Why it works: Nitrogen is a building block for proteins and chlorophyll. Its deficiency stops photosynthesis and growth.

Potassium (K) — fruit quality and winter hardiness

Deficiency symptoms (Westwood, 1993; Neilsen & Neilsen, 2003):

Leaf margins turn yellow and dry out — 'marginal scorch'. Starts on lower leaves, moves upward.
Leaves become wrinkled, curl downward.
Fruit are small, pale, low in sugar, store poorly.
Winter hardiness decreases.

What to do:

Apply potassium fertilisers in autumn or spring — potassium sulfate (40–60 kg/ha a.i.) or potassium magnesium sulfate. Avoid potassium chloride — chloride inhibits apple trees (Trunov, 2012).
For quick action — spray with 0.5–1% potassium sulfate solution on leaves during fruit growth (Mandal et al., 2021).

Why it works: Potassium regulates water balance, activates enzymes, and participates in sugar transport. It is especially important during fruit filling.

Phosphorus (P) — roots and fruiting

Deficiency symptoms (Neilsen & Neilsen, 2003; Rieger, 2010):

Rare symptom, appears on acidic or heavily compacted soils.
Leaves are dark green with a purple or bronze tint (accumulation of anthocyanins).
Stunted growth, weak flowering, poor fruit set.
Roots are underdeveloped; the tree establishes poorly after planting.

What to do:

Apply superphosphate at planting (100–150 g per planting hole) or in autumn under digging (40–60 kg/ha a.i.) (Ferree & Warrington, 2003).
On alkaline soils, phosphorus is poorly available — apply it locally, in the root zone.

Why it works: Phosphorus is key to energy metabolism (ATP) and the formation of roots, flowers, and seeds.

Calcium (Ca) — fruit health

Deficiency symptoms (Westwood, 1993; Neilsen & Neilsen, 2003; Ferree & Warrington, 2003):

Bitter pit — dark, sunken spots appear on fruit; the flesh underneath is dry and bitter. Spots may be single or numerous, often near the calyx (Plate 12.3 in Ferree & Warrington, 2003).
Cork spot — internal areas of flesh become dry and corky.
Young leaves are small, deformed, with curled edges; internodes are shortened.
Fruit crack and store poorly.

What to do:

Apply calcium foliarly — 0.5–1% solution of calcium chloride or calcium nitrate. Spray fruit 4–5 times at 7–10 day intervals, starting from the fruit growth stage (Neilsen & Neilsen, 2003; Mandal et al., 2021).
Do not over‑fertilise with nitrogen and potassium — they are antagonists of calcium. Optimal leaf N:Ca ratio — no more than 10:1 (Westwood, 1993).
Maintain even soil moisture — drought disrupts calcium transport into fruit.

Why it works: Calcium strengthens cell walls and membranes. It enters fruit mainly through transpiration in the early stages of growth — hence the importance of early summer irrigation and foliar feeding.

Magnesium (Mg) — photosynthesis

Deficiency symptoms (Neilsen & Neilsen, 2003; Buckingham, 2010):

Interveinal chlorotic yellowing appears on older leaves, veins remain green. Starts on lower leaves.
In severe deficiency, leaves turn red, brown, and drop (Plate 12.2 in Ferree & Warrington, 2003).
Fruit become smaller, sugar content drops.

What to do:

Apply magnesium sulfate (potassium magnesium sulfate) to the soil — 200–300 g per tree (Krivko, 2014).
Foliar feed — 2% magnesium sulfate (Epsom salts) solution during shoot growth (Neilsen & Neilsen, 2003; Mandal et al., 2021).

Why it works: Magnesium is the central atom of the chlorophyll molecule. Without it, photosynthesis is impossible.

Iron (Fe), Manganese (Mn), Zinc (Zn) — 'chlorosis' elements

Iron deficiency symptoms (lime‑induced chlorosis) (Neilsen & Neilsen, 2003; Buckingham, 2010):

Young upper leaves turn yellow, veins remain green. The leaf blade is almost white, while veins are contrasting green (Plate 12.9 in Ferree & Warrington, 2003).
Often appears on carbonate (calcareous) soils with pH > 7.5.

Manganese deficiency (Neilsen & Neilsen, 2003):

Similar to iron chlorosis, but affects older leaves; interveinal chlorosis is uneven, patchy (Plate 12.10 in Ferree & Warrington, 2003).
Angular light‑green spots may appear on apple leaves.

Zinc deficiency (Neilsen & Neilsen, 2003; Buckingham, 2010):

Little‑leaf, narrow deformed leaves clustered in 'rosettes' at shoot tips (Plate 12.8 in Ferree & Warrington, 2003).
Shoots have shortened internodes, terminal buds fail to develop.
Fruit are small and misshapen.

What to do:

On alkaline soils, apply iron chelates (Fe‑EDDHA) to soil or as foliar spray (Neilsen & Neilsen, 2003).
Zinc and manganese are more effective as foliar feeds: zinc sulfate (0.05–0.1%) + hydrated lime for neutralisation; manganese sulfate (0.05–0.1%) (Mandal et al., 2021; Krivko, 2014).
Improve soil structure, add organic matter, acidify pH if necessary (with sulfur, ammonium sulfate) to 6.0–6.5 — then these elements become more available.

Why it works: Iron, manganese, and zinc participate in chlorophyll synthesis and enzymatic reactions. In alkaline conditions, their ions form insoluble compounds unavailable to roots.

Boron (B) — flowering and fruiting

Deficiency symptoms (Westwood, 1993; Neilsen & Neilsen, 2003):

Poor fruit set, 'blind' flowers, blossom blast (Plate 12.5 in Ferree & Warrington, 2003).
Young leaves are deformed, thickened, margins curled.
Fruit have hard corky areas inside ('dry spot'), externally — dents and cracks (Plate 12.6 in Ferree & Warrington, 2003).
Dieback of shoot tips, bark cracking (corky bark).

What to do:

Foliar feed — 0.1–0.15% boric acid or 'Solubor' — before and after flowering (Neilsen & Neilsen, 2003; Mandal et al., 2021).
To soil — occasionally, 1–2 kg/ha boron, no more than once every 3 years, as boron easily reaches toxic concentrations (Neilsen & Neilsen, 2003).

Why it works: Boron stimulates pollen tube growth and fertilisation, participates in carbohydrate transport. Deficiency most often occurs on light, leached soils and in dry years.

3.2. Excess of Elements — Also a Problem

An over‑fed apple tree is no less vulnerable than a hungry one.

Nitrogen excess (Neilsen & Neilsen, 2003; Westwood, 1993):

Vigorous shoot growth continuing until late autumn; wood does not ripen, winter hardiness decreases.
Fruit are large but watery, store poorly; skin remains green even on red‑skinned varieties.
Increased susceptibility to diseases (powdery mildew, scab) and pests (aphids).
Calcium content in fruit drops sharply — bitter pit worsens.

Potassium excess (Westwood, 1993; Neilsen & Neilsen, 2003):

Inhibits uptake of calcium and magnesium, provoking bitter pit.
Glassy spots may appear on fruit.
Leaves may take on a dark‑green shade with a bluish bloom.

Boron excess (Neilsen & Neilsen, 2003):

Leaf margins turn brown and die (toxic necrosis) (Plate 12.7 in Ferree & Warrington, 2003).
Fruit set decreases, fruit ripen prematurely and drop. Toxicity occurs when leaf boron exceeds 50–70 ppm.

Manganese excess (Neilsen & Neilsen, 2003; Westwood, 1993):

On acidic soils (pH < 5.5), manganese can accumulate to toxic levels.
Manifests as 'internal bark necrosis' (bark measles) — bark swells, cracks, and peels off on the trunk and large branches.

What to do in case of excess:

Stop applying the corresponding fertiliser.
Increase irrigation to leach excess salts from the root zone (on drained soils).
For acidic soils — liming (pH 6.0–6.5) reduces manganese availability (Westwood, 1993).
For boron excess — irrigation, application of gypsum or organic matter that binds boron.

3.3. Nutrient Imbalance: Not Just Levels but Ratios

Imbalance occurs when elements are present in sufficient amounts, but their ratios interfere with each other's uptake.

Classic example: antagonism between potassium, calcium, and magnesium (Westwood, 1993; Neilsen & Neilsen, 2003):

High potassium interferes with calcium and magnesium uptake. Leaf K:Ca > 2 — risk of bitter pit.
High magnesium also reduces calcium uptake.
Optimal leaf ratios: K:Ca — 1.2–1.5, Mg:Ca — 0.8–1.2 (Neilsen & Neilsen, 2003).

N:Ca ratio:

If N:Ca > 30 — fruit store poorly and develop physiological disorders (Westwood, 1993).
Optimal leaf N:Ca — 10:1; in fruit — no more than 30:1 (Mandal et al., 2021).

K:N and K:Mg ratios:

Excess potassium relative to magnesium and nitrogen weakens the tree, causing chlorosis of older leaves.

What to do:

Use balanced complex fertilisers (NPK + Mg + micronutrients) — 'Kristalon', 'Master', 'Poly‑feed' (Krivko, 2014).
Conduct leaf diagnostics — analysis of middle leaves from current‑year shoots in July–August will show the real element ratios (Neilsen & Neilsen, 2003).
Apply fertilisers fractionally, according to growth stages: spring — nitrogen; fruit growth period — potassium and calcium; autumn — phosphorus and potassium (Trunov, 2012).

Practical Table: How to Diagnose Nutritional Disorders from Leaves and Fruit

Symptom	Likely Cause	What to Do
Leaves pale‑yellow, small; shoots short	Nitrogen deficiency	Spring — urea or ammonium nitrate
Leaf margins yellow and dry; fruit small	Potassium deficiency	Potassium sulfate in autumn or foliar in summer
Leaves dark with purple tint; weak growth	Phosphorus deficiency	Superphosphate in autumn, locally in root zone
Fruit with dark sunken spots (bitter pit)	Calcium deficiency	Foliar CaCl₂ or Ca(NO₃)₂
Interveinal chlorosis on old leaves, veins green	Magnesium deficiency	Magnesium sulfate to soil or foliar
Young leaves yellow, veins green, on calcareous soil	Iron deficiency (chlorosis)	Iron chelates foliar/soil; acidify soil
Small narrow leaves in rosettes; short shoots	Zinc deficiency	Zinc sulfate foliar (0.05–0.1%)
Dry corky spots inside fruit; poor fruit set	Boron deficiency	Boric acid foliar before and after flowering
Brown necrosis of leaf margins; premature fruit ripening	Boron excess	Stop application; irrigation; organic additives

4. Environmental Damage

Even with ideal nutrition and watering, apple trees can suffer from weather anomalies and pollution. Frost, heat, sunburn, polluted air, and soil salinity cause characteristic damage that can easily be confused with diseases. In this chapter, we will look at how to recognise such disorders and protect your orchard.

4.1. Frost and Winter Damage

The apple tree is one of the most winter‑hardy fruit crops, but it still suffers from severe frosts, thaws, and spring frosts. Frost resistance changes during the year: in winter, in deep dormancy, the tree can withstand –40 °C, but in spring even –2 to –3 °C can kill flowers (Westwood, 1993; Trunov, 2012).

Winter Sun Scald (Frost Cracks)

How to recognise (Krivko, 2014; Westwood, 1993):

On the southern and southwestern side of the trunk and large branches, bark turns brown, cracks, and peels.
Affected bark dies, exposing wood; a callus roll forms at the boundary between healthy and damaged tissue.
Trees with smooth dark bark and those growing in open sites are more often affected.

Why this happens. In winter, especially in late winter – early spring, daytime sun heats dark bark to +10…+15 °C; cambium cells break dormancy and start to grow. At night, temperatures drop, and the awakened tissues die. Damage accumulates year after year, weakening the tree and opening the door to fungal infections (Westwood, 1993; Krivko, 2014).

What to do:

Whitewash trunks and bases of scaffold branches — in autumn, before sustained frost (preferably in November–December). Mix: 2 kg fresh slaked lime + 0.5 kg copper sulfate + 0.2 kg casein glue per 10 L water. Spring whitewash is decorative but useless for sunburn protection, as the cambium is already damaged in winter (Krivko, 2014).
Wrap the trunk — for young trees and thin‑barked varieties, wrap the trunk with light‑coloured agrotextile, thick paper, or reed mats for winter, removing in spring.
Proper training — a low trunk (40–60 cm) reduces the heated surface area (Trunov, 2012).
Choose resistant varieties — varieties with light bark ('Antonovka', 'Grushovka Moskovskaya') suffer less than 'Renet Simirenko' and others (Krivko, 2014).

Damage to Buds and Flowers by Spring Frosts

Spring frosts are the main cause of crop failure in many regions. Critical temperatures for different flower development stages (Proebsting & Mills, 1978; Westwood, 1993):

Stage of Development	Temperature for 10% kill	Temperature for 90% kill
Bud swelling	–7…–9 °C	–14…–16 °C
Pink bud	–4…–5 °C	–7…–9 °C
Full bloom	–2…–3 °C	–3…–4 °C
Young fruit set	–1.5…–2 °C	–2.5…–3 °C

How to recognise damage:

The central (king) flower turns brown, dries up — it usually opens first and is most sensitive (Jackson, 2003).
Fruit set does not develop, drops; fruit with damaged seeds grows lopsided.
Watery spots appear on young leaves, then turn brown and die.

What to do for protection:

Choose sites with good air drainage — on elevations, cold air flows downhill, frosts are milder (Westwood, 1993).
Delay flowering — in autumn (September–October), spray with 0.01–0.02% NAA (naphthaleneacetic acid) to delay bud break in spring by 5–7 days (Krivko, 2014). Late‑flowering varieties ('Antonovka', 'Korichnoye Polosatoye') suffer less from return frosts.
Use smoking — when temperature drops to 0…–1 °C, light smoke piles (at least 75 per ha) or use smoke generators (Krivko, 2014). The smoke screen reduces heat radiation from the soil and can raise temperature by 0.5–1.5 °C.
Sprinkler irrigation — continuous fine‑spray irrigation during frost releases heat as water freezes, protecting flowers, but requires a reliable system and large volumes of water (Westwood, 1993).
Covering — for young orchards or dwarf forms, use agrotextile (spunbond) overnight during flowering.

4.2. Heat and Sunburn

High temperatures and intense solar radiation damage not only fruit but also bark, especially on the southern side of the trunk and on fruit not protected by foliage.

Fruit Sunburn

How to recognise (Mandal et al., 2021; Rieger, 2010):

On the sun‑exposed side of the fruit, pale, yellowish or brown patches appear, which darken over time to brown, become sunken and dry (necrosis).
The skin at the burn site cracks and becomes rough; the fruit loses marketability and spoils quickly in storage.

Why this happens. Direct sunlight heats the fruit skin to 45–52 °C. This causes protein denaturation and destruction of cell membranes. Fruit on the southern side of the canopy, under moisture deficit and sudden temperature changes, are especially affected (Colavita et al., 2011; Racsko & Schrader, 2012).

Risk factors: bare branches without leaves, hot weather combined with drought, thin‑skinned varieties ('Golden Delicious', 'Granny Smith').

What to do:

Train the canopy with good leaf cover — leaves protect fruit from overheating (Trunov, 2012).
Irrigation on hot days — fine‑spray sprinkling (or water spraying) reduces fruit surface temperature by 5–8 °C (Racsko & Schrader, 2012).
Protective screens — spraying fruit with kaolin (clay) suspension reflects sunlight, reduces temperature, and prevents burns (Colavita et al., 2011; Mandal et al., 2021).
Shade nets — in regions with very intense sun, stretch shade nets over trees (20–30% shading), which also reduces heat stress and improves fruit colour.

Bark Sunscald

How to recognise (Westwood, 1993; Krivko, 2014):

On the southern side of the trunk and main branches, bark becomes brownish‑red, flakes, and peels off from the wood.
In summer, scalds appear as dry cracks; in winter — as frost cracks, which often exacerbate each other.

What to do:

Same measures as for winter burns — whitewashing, wrapping, training.
Leave 'protective' branches (temporary) on the trunk to shade it during the first 3–4 years.

4.3. Air Pollution

Near industrial centres, highways, and in conditions of temperature inversions, apple trees can suffer from gaseous pollutants. The most dangerous are ozone (O₃), sulfur dioxide (SO₂), peroxyacetyl nitrate (PAN), ethylene, and nitrogen dioxide (NO₂) (Hochmuth & Sideman, 2023).

Ozone (Hochmuth & Sideman, 2023):

On the upper surface of mature leaves, small dark‑brown or black spots ('stippling') appear, later becoming whitish or silver.
Leaves may yellow and drop prematurely. Thin‑leaved varieties are particularly affected.

Sulfur dioxide (Hochmuth & Sideman, 2023):

Bleaching of tissue between veins (necrosis) — from pale yellow to brown. Mainly fully developed leaves are affected; young leaves are more resistant.
With severe pollution — defoliation and reduced growth.

Ethylene — a ripening hormone that at high concentrations (e.g., from exhaust fumes or industrial emissions) causes physiological disorders (Hochmuth & Sideman, 2023):

Premature yellowing and leaf drop.
Accelerated ripening and fruit drop, reduced storage life.
Disruption of flower bud differentiation.

What to do:

Choose a site at least 200–300 m away from highways and industrial plants.
Plant windbreak strips — they trap some of the polluted air.
Water and feed the trees — healthy plants are more resistant to gaseous damage.
Varieties with high resistance — for industrial zones, choose less sensitive apple varieties (e.g., 'Antonovka', 'Pepin Shafranny').

4.4. Salt Stress

In arid regions and on irrigated lands with mineralised water, apple trees may suffer from excess soluble salts in the soil.

How to recognise salt stress (Westwood, 1993; Krivko, 2014):

Leaves become dark green with a bluish tint, then margins and tips turn brown and die ('marginal scorch', similar to potassium deficiency).
In severe salinity, leaves are small, tree is stunted, shoots are short.
Cracks and gummosis may appear on the trunk bark (in stone fruits — more often, but in apple, less frequently).

Causes. Excess sodium chlorides and sulfates in the soil disrupt osmotic balance, and roots cannot absorb water even when it is present — causing 'physiological drought'. Apple is particularly sensitive to chloride salinity (Krivko, 2014).

Critical indicators (Westwood, 1993; Krivko, 2014):

Total mineralisation of irrigation water above 1.5–2.0 g/L is already dangerous.
Chloride content in the root zone > 0.3 meq/100 g soil.
Sulfate content > 2.0 meq/100 g soil.

What to do:

Use water with low mineralisation (< 0.5–1.0 g/L). When forced to use brackish water, increase irrigation rate by 15–20% — to leach salts from the root zone (Krivko, 2014).
Organic fertilisers and mulch improve soil structure, promote salt leaching, and reduce toxicity.
Apply gypsum (CaSO₄) on saline soils — calcium displaces sodium from the soil exchange complex (Westwood, 1993).
Choose more salt‑tolerant rootstocks — seedling rootstocks and MM.106 tolerate salinity better than dwarf clonal ones (M.9, M.26) (Ferree & Warrington, 2003).
Drip irrigation allows precise water application and reduces salt accumulation in the root zone compared to surface irrigation.

Quick Reference: How to Protect Apple Trees from Environmental Damage

Stress Factor	Symptoms	Main Protection Measures
Winter frost and bark sunscald	Cracks, peeling bark on southern side	Autumn whitewashing, trunk wrapping, low trunk
Spring frost	Browning and death of flowers, fruitlet drop	Delayed flowering (auxin sprays), smoking, agrotextile cover
Fruit sunburn	Brown sunken spots on fruit	Irrigation, kaolin, shade nets, good leaf cover
Air pollution (O₃, SO₂, ethylene)	Stippling, leaf discolouration, premature leaf fall	Site away from roads and factories, windbreaks, strengthen tree health
Soil salinity	Leaf marginal scorch, stunted growth	Good‑quality water, leaching irrigation, gypsum, tolerant rootstocks

5. Growth and Fruiting Disorders

Even with good care, an apple tree can disappoint: no crop at all, fruit small and cracked, fruit drop. This is not always diseases or pests — often the cause is physiological failure of the fruiting system itself. Let’s look at five main disorders, their causes, and correction methods.

5.1. Biennial Bearing (Alternate Bearing)

Biennial bearing (or alternate bearing) is the alternation of heavy‑crop and light‑crop years. This is well known to gardeners and is considered one of the main problems of apple trees (Jackson, 2003; Krivko, 2014).

How to recognise:

In one year, the tree is literally loaded with fruit; the next year, flowering is sparse or absent.
Heavy years alternate with light years, and the cycle may be regular (every other year) or irregular.
Varieties particularly prone to biennial bearing: 'Golden Delicious', 'Jonagold', 'Spartan', 'Oregon Spur Delicious', and many old cultivars (Ferree & Warrington, 2003; Jackson, 2003).

Why this happens. Flower buds are initiated in the previous year's summer (June–July). If the tree is overloaded with fruit, all resources go into growing them, leaving no energy for new flower bud initiation. Seeds in fruit produce hormones (gibberellins) that suppress flower bud formation (Jackson, 2003). The next year, the tree 'rests' and initiates an excessive number of buds — and the cycle repeats (Westwood, 1993; Krivko, 2014).

What to do to smooth out biennial bearing:

1. Crop load regulation. Remove some flowers or fruitlets to prevent overloading. Optimal load — no more than 4–6 fruit per 1 cm² of trunk cross‑section (Krivko, 2014).

2. Chemical thinning. At full bloom or shortly after (when fruitlets are 9–12 mm), spray with 0.01–0.02% NAA (naphthaleneacetic acid) or carbaryl (following instructions). This causes part of the fruitlets to drop (Westwood, 1993; Ferree & Warrington, 2003).

3. Adjust pruning. Summer pruning (July–August) reduces shoot growth and stimulates flower bud initiation. Autumn or spring pruning also helps balance the load (Trunov, 2012).

4. Maintain a healthy leaf canopy. The more healthy leaves, the more carbohydrates for bud initiation. Control scab, powdery mildew, and aphids (Krivko, 2014).

It is important to understand: completely eliminating biennial bearing in genetically predisposed varieties is difficult, but smoothing it out is realistic.

5.2. Fruitlet Drop (June Drop)

In late May–June (in the Northern Hemisphere), the apple tree sheds some young fruitlets. This is a normal self‑regulation process — the tree gets rid of fruitlets it cannot 'feed'. However, when drop becomes massive, exceeding 90–95% of the flowers, it is a disorder (Agustí, 2010; Krivko, 2014).

How to recognise:

Young fruitlets (size 1–3 cm) drop in large numbers in late spring – early summer.
Those with few seeds (lopsided) or damaged by pests drop first.
Normally, only 5–10% of flowers remain — this is the 'useful set' (Jackson, 2003; Krivko, 2014).

Causes of excessive drop:

Water shortage during fruitlet growth (April–June). Drought weakens fruit growth and provokes drop (Westwood, 1993; Mandal et al., 2021).
Nutrient deficiency — especially nitrogen and potassium in the first half of summer.
Poor pollination — few seeds in fruitlets, so they do not produce enough hormones to hold the fruit (Jackson, 2003).
Excessive shoot growth — strong shoot growth competes with fruitlets for assimilates (Trunov, 2012).
Shading — insufficient light reduces photosynthesis and intensifies competition (Ferree & Warrington, 2003).

What to do to reduce drop:

Provide irrigation during flowering and for 4–6 weeks after. Water every 7–10 days, wetting the soil to 40–50 cm (Mandal et al., 2021; Krivko, 2014).
Apply nitrogen‑potassium fertiliser 2–3 weeks after flowering (20–30 g/m² of crown projection) — this supports fruitlet growth (Neilsen & Neilsen, 2003).
Improve pollination — plant polliniser varieties nearby or use artificial pollination (manually or with bumblebees) in unfavourable years (Jackson, 2003).
Remove some flowers in heavy bloom — artificial thinning reduces competition and improves quality of remaining fruit (Westwood, 1993).

5.3. Small Fruit Size

Fruit become smaller than the normal size for the variety, even though they appear healthy externally. This reduces market value and yield.

Causes:

Crop overload — too many fruit, and the tree cannot 'feed' them all. The flip side of biennial bearing: in a heavy year, fruit are always smaller (Ferree & Warrington, 2003).
Lack of water and nutrients during fruit growth (June–August). Potassium is especially important for fruit filling (Neilsen & Neilsen, 2003).
Poor leaf surface — too few leaves per fruit. Optimum for apple — 30–40 leaves per fruit (Westwood, 1993; Jackson, 2003).
Root damage (digging, compaction, diseases) — roots cannot supply fruit with nutrients (Krivko, 2014).
Tree aging — old trees produce smaller fruit even with good care (Westwood, 1993).

What to do:

Crop load regulation — leave no more than one fruit per 4–6 cm of branch length, or one fruit per cluster (for large‑fruited varieties) (Krivko, 2014).
Provide potassium nutrition — during fruit filling (July–August), apply potassium sulfate (30–40 g/m²) or foliar feed with 0.5–1% potassium sulfate (Neilsen & Neilsen, 2003).
Improve canopy light penetration — proper pruning for an open centre. Fruit on well‑lit branches are always larger (Ferree & Warrington, 2003).
Water evenly — sharp moisture fluctuations stop fruit growth and reduce size (Westwood, 1993).
Rejuvenate old trees — heavy pruning stimulates young shoot growth and improves fruit quality (Trunov, 2012).

5.4. Fruit Cracking

Fruit crack, especially just before harvest. Cracks spoil appearance and open the door to rots and fungi.

How to recognise:

Deep or superficial cracks appear on the skin, often radial (from stalk to calyx) or concentric around the calyx.
Thin‑skinned varieties are particularly prone: 'Golden Delicious', 'Cox Orange Pippin', 'Gala' (Jackson, 2003; Westwood, 1993).

Causes (Jackson, 2003; Westwood, 1993):

Sharp moisture fluctuations — after drought, heavy watering or rain. The skin cannot stretch fast enough to keep up with the rapidly swelling flesh.
Calcium deficiency — weakens cell walls of the skin, making it less elastic (Neilsen & Neilsen, 2003).
High temperatures during filling — accelerate flesh growth while skin lags behind.
Nitrogen excess — stimulates excessively rapid fruit growth, skin 'bursts' (Westwood, 1993).

What to do:

Water evenly — avoid long watering breaks during fruit growth. Drip irrigation is best (Mandal et al., 2021).
Calcium feeds — foliar treatments with 0.5–1% calcium chloride or calcium nitrate 3–4 weeks before harvest strengthen the skin (Neilsen & Neilsen, 2003; Ferree & Warrington, 2003).
Do not over‑feed nitrogen — limit nitrogen applications in the second half of summer.
Choose crack‑resistant varieties — e.g., 'Granny Smith', 'Jonagold', or 'Fuji' are less prone (Rieger, 2010).
Mulch the soil — it smooths out moisture fluctuations.

5.5. Internal Physiological Disorders of Fruit

These are disorders that appear inside the fruit, often only when cut or after storage. They significantly reduce storage life and marketable quality.

Bitter Pit (Bitter pit)

This is the best‑known internal disorder of apple (Ferree & Warrington, 2003; Westwood, 1993).

Symptoms:

On the skin — dark, slightly sunken spots, often near the calyx.
Inside — dry, corky areas of flesh, bitter to taste.
Appears on the tree, but more often during storage.

Cause: calcium deficiency in fruit due to nutritional imbalance, drought, crop overload, or vigorous shoot growth (Neilsen & Neilsen, 2003).

What to do: see the calcium section in Chapter 3 (foliar feeds, moisture maintenance, element balance).

Watercore

Symptoms:

The flesh in the centre of the fruit becomes translucent, watery, glassy (Westwood, 1993; Ferree & Warrington, 2003).
Often found in 'Golden Delicious', 'Fuji', 'Cox'.
In moderate degree, it does not spoil taste but reduces storage life.

Cause: accumulation of sorbitol (sugar) in intercellular spaces due to metabolic disturbance. Often triggered by too‑late harvest, heavy irrigation before picking, high nitrogen rates (Westwood, 1993; Jackson, 2003).

What to do:

Harvest fruit on time, avoiding over‑ripeness.
Do not over‑feed nitrogen in the second half of summer.
Do not store watercore‑affected fruit long‑term.

Internal Browning (Brown Core)

Symptoms:

Flesh inside the fruit turns brown, dry or moist, especially in the core and around seed cavities (Westwood, 1993; Ferree & Warrington, 2003).
Often appears after long storage.

Causes:

Low temperatures (chilling injury) — in cold‑sensitive varieties ('McIntosh', 'Cox') stored below 0…+2 °C (Westwood, 1993).
Low oxygen or high CO₂ in the storage (gas regime disturbance).
Over‑ripeness on the tree or unbalanced nutrition (Ferree & Warrington, 2003).

What to do:

Maintain optimal storage temperature for each variety (e.g., for 'McIntosh' — +2…+4 °C, for 'Golden' — 0…+1 °C) (Westwood, 1993).
Monitor O₂ and CO₂ levels in storage (not below 2–3% O₂, not above 3–5% CO₂ for most varieties) (Ferree & Warrington, 2003).
Harvest at optimal maturity, not over‑ripe.
Apply calcium feeds to increase tissue resistance (Neilsen & Neilsen, 2003).

Superficial Scald

Symptoms:

Brown, irregularly shaped patches appear on the fruit skin, like a 'scald' (Plate 9 in Agustí, 2010; Ferree & Warrington, 2003).
Develops in cold storage after 2–4 months.

Cause: oxidation of α‑farnesene (a natural compound in the skin) under low temperatures. Genetically predisposed varieties: 'Granny Smith', 'Red Delicious', 'Roma' (Westwood, 1993; Ferree & Warrington, 2003).

Prevention:

Use antioxidant treatments (diphenylamine — DPA) immediately after harvest (in commercial orchards) (Ferree & Warrington, 2003).
For home gardens: harvest early, not over‑ripe; do not store scald‑prone varieties long‑term.
Use controlled atmosphere (reduced O₂ — 1.5–2.5%) in storage — reduces risk (Ferree & Warrington, 2003).

Cork Spot (Lenticel Blotch)

Symptoms:

Under the skin or deeper — dry corky areas, often near the calyx or in the flesh (Westwood, 1993).
Externally may appear as small sunken spots.

Cause: calcium starvation, similar to bitter pit, but manifests differently. Often linked to uneven watering (Neilsen & Neilsen, 2003).

What to do: same measures as for bitter pit — calcium feeds and moisture regulation.

Quick Reference: Fruiting Disorders and Their Correction

Disorder	Main Causes	Prevention Measures
Biennial bearing	Crop overload, suppressed bud initiation	Flower thinning, fruitlet thinning, balanced pruning
Fruitlet drop	Water shortage, poor pollination, nutrient deficit, excessive shoots	Irrigation at flowering–growth, N+K feeding, improve pollination
Small fruit size	Overload, K deficiency, poor light, aging	Crop regulation, K feeds, pruning, irrigation
Fruit cracking	Sharp moisture fluctuations, Ca deficit, N excess	Even watering, Ca feeds, limit N
Bitter pit	Ca deficit, N:Ca imbalance, drought	Foliar Ca, irrigation, maintain N:Ca ratio
Watercore	Late harvest, N excess, heavy irrigation	Timely harvest, limit N and irrigation before picking
Internal browning	Chilling injury, gas regime disturbance in storage	Optimal temperature (+2…+4 °C), control O₂ and CO₂
Superficial scald	Genetic predisposition, long storage	Antioxidant treatments (commercial), early harvest, controlled atmosphere

6. Prevention of Physiological Disorders

The best way to deal with physiological disorders is to prevent them. Prevention rests on three pillars: proper cultivation practices, regular monitoring, and timely stress prevention. This chapter combines everything we have discussed into a system of practical actions.

6.1. Optimal Cultivation — The Foundation of Health

A healthy apple tree is one that receives everything it needs at the right time and in the right amounts. Cultivation should be balanced and aligned with the tree's phenological stages.

Soil and Planting

Choose a site with deep (at least 1.5–2 m), well‑drained soils, pH 6.0–7.0. On acidic soils (pH < 5.5), apply lime; on alkaline soils (pH > 7.5), acidify with peat or sulfur (Westwood, 1993; Ferree & Warrington, 2003).
Avoid sites with high groundwater (closer than 1.5–2 m to the surface) and stagnant moisture — this leads to root rots and chlorosis (Krivko, 2014).
At planting, apply phosphorus‑potassium fertilisers (superphosphate + potassium sulfate) in the planting hole, but do not overuse nitrogen — it delays establishment (Neilsen & Neilsen, 2003; Trunov, 2012).
Consider rootstock and scion compatibility — different rootstocks tolerate drought, waterlogging, and salinity differently. For light soils — more drought‑tolerant seedling rootstocks and MM.106; for heavy soils — less aerating‑demanding M.7 or MM.106 (Ferree & Warrington, 2003).

Irrigation and Moisture

Water regularly at critical phases: flowering, fruit growth (June–July), fruit filling (4–8 weeks before harvest). Rate — 50–60 L/m² of crown projection per watering, but better to follow soil moisture (optimal 75–80% of field capacity) (Westwood, 1993; Mandal et al., 2021).
Avoid sharp moisture fluctuations — watering should be even, with intervals of 7–10 days in hot weather. Drip irrigation and mulching are your best allies (Krivko, 2014).
In autumn, if dry, carry out pre‑winter irrigation (up to 100–120 L/m²) — it increases winter hardiness and sets the stage for spring growth (Trunov, 2012).

Nutrition (Fertilisation)

The fertilisation system should take into account not only deficiencies but also the balance of elements. Use the principle 'adjust based on analysis, not intuition'.

Basic rules:

Nitrogen — apply in spring (in 2–3 doses: before flowering and after fruit set) at 30–60 kg/ha a.i. for mature orchards. On poor soils — 60–90 kg/ha. Nitrogen excess is more dangerous than deficiency (Neilsen & Neilsen, 2003; Ferree & Warrington, 2003).
Phosphorus and potassium — apply in autumn (under digging) at 40–60 kg/ha a.i. each. On sandy soils, potassium may leach, so apply it in split doses (Westwood, 1993; Trunov, 2012).
Calcium — apply foliarly (on leaves and fruit) 4–5 times per season, starting from the fruit growth stage. Use calcium chloride or calcium nitrate at 0.5–1% concentration (Neilsen & Neilsen, 2003; Mandal et al., 2021).
Micronutrients (B, Zn, Mn, Fe) — apply foliarly at the first signs of deficiency. For prevention, 1–2 treatments per season are sufficient (Neilsen & Neilsen, 2003; Krivko, 2014).
Organic matter — apply well‑rotted manure or compost once every 3–4 years (4–6 kg/m²) to improve soil structure and increase buffering capacity (Westwood, 1993; Trunov, 2012).

Monitor leaf element ratios (July analysis of middle leaves from current‑year shoots):

Ratio	Optimal Value	What to Do if Deviated
N : Ca in leaves	≤ 10 : 1	If >10 — reduce N, increase Ca
K : Ca in leaves	1.2–1.5 : 1	If >1.5 — reduce K, increase Ca
Mg : Ca in leaves	0.8–1.2 : 1	If >1.2 — reduce Mg, increase Ca

Pruning and Training

Train the canopy for good light penetration to all leaves — a sparse‑tiered or spindle‑shaped canopy allows light into the centre (Trunov, 2012; Krivko, 2014).
Remove branches growing inward and overcrowding — reduces shading and fungal diseases, and improves fruit quality (Ferree & Warrington, 2003).
Rejuvenate old trees with heavy pruning (shortening to 3–5‑year‑old wood) — stimulates young shoot growth, improves fruiting, and reduces biennial bearing (Westwood, 1993).
Regulate the load — when pruning, leave 4–6 buds per shoot to keep flower numbers moderate. This reduces crop overload and improves fruit quality (Krivko, 2014).

6.2. Tree Monitoring — Your Eyes and Ears in the Orchard

Regular orchard inspections are the main tool for early detection of disorders. Do not wait for obvious symptoms — prevention starts with observation.

What and How to Check:

1. Leaves — assess colour, size, shape, spots, and chlorosis. Check upper and lower leaves, old and young.

Uniform yellowing of old leaves → nitrogen deficiency.
Yellow veins on green leaves → iron (chlorosis) or manganese deficiency.
Marginal scorch → potassium deficiency or salt stress.

2. Shoots — measure current‑year growth length. For a healthy bearing tree, shoot length should be 30–50 cm. If less than 20 cm → nutritional weakness or crop overload (Westwood, 1993; Trunov, 2012).

3. Fruit — assess size (compared to variety average), shape, spots, cracks, and watercore.

Bitter pit, cork spot → calcium deficiency.
Cracking → sharp moisture fluctuations or calcium deficiency.
Small size → overload or lack of potassium/water (Ferree & Warrington, 2003).

4. Bark and trunk — inspect for cracks, swellings, peeling, especially on the southern side. This will help you notice sunscald and frost cracks in time (Krivko, 2014).

5. Root system (indirectly) — stunted growth, chlorosis, poor fruiting may indicate root problems (waterlogging, compaction, soil‑working damage) (Westwood, 1993).

Monitoring frequency:

Weekly during active growth (May–August).
After every heavy rain or frost — an extra inspection.
In autumn and spring — a detailed inspection of the whole tree, including bark and bud condition.

6.3. Stress Prevention — Proactive Protection

Most physiological disorders are triggered by stress factors. The better you prepare the tree for stress, the less damage there will be.

Protection from Drought and Heat

Mulching the trunk circle (layer 8–10 cm of peat, compost, straw, mown grass) retains moisture and reduces soil overheating (Krivko, 2014; Mandal et al., 2021).
Drip irrigation — the most reliable way to maintain root‑zone moisture without waterlogging or sharp fluctuations (Trunov, 2012).
Shade nets or shading in southern regions reduce fruit sunburn (Colavita et al., 2011; Racsko & Schrader, 2012).

Protection from Frost and Freezes

Autumn whitewashing of trunks and branch bases — protects from winter sunscald (Krivko, 2014).
Wrapping the trunk for winter for young trees (agrotextile, paper, reeds) — prevents frost cracks (Westwood, 1993).
Delayed flowering (spraying with NAA or gibberellins in autumn) reduces spring frost risk (Krivko, 2014; Jackson, 2003).
Smoking and sprinkling during frosts — to protect flowers and fruitlets (Westwood, 1993; Krivko, 2014).

Protection from Salt Stress

Use water with low mineralisation (< 1 g/L) for irrigation (Krivko, 2014).
Apply leaching irrigation — extra water (15–20% above normal) helps wash salts from the root zone (Westwood, 1993).
Apply gypsum and organic matter to improve structure and reduce salt toxicity (Westwood, 1993; Trunov, 2012).

Protection from Air Pollution

Choose sites away from highways and industrial zones (at least 200–300 m).
Create windbreak strips — they trap some polluted air.
Maintain overall tree health — healthy plants are more resistant to gaseous damage (Hochmuth & Sideman, 2023).

Final Summary: A System for Preventing Physiological Disorders in Apple Trees

Area	Specific Actions	Frequency
Soil and planting	Drainage, pH 6.0–7.0, P‑K in planting hole, rootstock choice	Before planting, then once every 3–4 years — liming/acidification
Irrigation	Regular watering at critical phases, mulching, drip irrigation	Weekly in dry weather; pre‑winter irrigation in autumn
Nutrition	Balanced fertilisation, foliar Ca and micronutrients, control of N:Ca, K:Ca ratios	Throughout the season, especially spring–summer; leaf analysis in July
Pruning	Open‑centre training, load regulation, rejuvenation of old trees	Annually (winter–early spring); summer (sanitary)
Monitoring	Regular inspections of leaves, shoots, fruit, bark; leaf nutrient analysis	Weekly during growth; analysis every 2–3 years
Stress protection	Whitewashing, wrapping, smoking, shading, salinity control	By season (autumn–winter–spring) and according to weather
Fruiting regulation	Fruitlet and flower thinning, load regulation	During flowering and fruitlet growth (May–June)

Key takeaway: physiological disorders of apple trees are not a death sentence. Unlike infectious diseases, they are often reversible if the cause is identified in time and eliminated. Systematic care, attention to the tree's signals, and timely correction of cultivation practices are the best prevention. May your orchard be healthy and generous!

References

Agusti, M. (2010). ‘Prolongacion de la vida del fruto. Tecnicas poscosecha’, in Fruticultura. Madrid, Spain: Ediciones Mundi-Prensa, pp. 161-178.
Buckingham, A. (2010). ‘Apples’, in Grow Fruit. New York, NY: DK Publishing, pp. 41-80.
Buckingham, A. (2010). ‘Fruit Doctor’, in Grow Fruit. New York, NY: DK Publishing, pp. 314-341.
Colavita, G.María., Curetti, M., Raffo, D., Sosa, M.Cristina., Vita, L.I. (2021). ‘Apple’, in Mandal, D., Wermund, U., Phavaphutanon, L., Cronje, R. (ed.) Temperate Fruits. Production, Processing, and Marketing. Burlington, Canada: Apple Academic Press, pp. 1-106.
Hochmuth, G.J., Sideman, R.G. (2023). ‘Wegetable Pests and Problems’, in Knott's Handbook for Vegetable Growers. : John Wiley & Sons, pp. 365-452.
Jackson, J.E. (2003). ‘Flowers and fruits’, in Biology of Apples and Pears. Cambridge, UK: Cambridge University Press, pp. 268-340.
Neilsen, G.H., Neilsen, D. (2003). ‘Nutritional Requirements of Apple’, in Ferree, D.C., Warrington, I.J. (ed.) Apples: botany, production, and uses. Cambridge, MA: CABI, pp. 267-302.
Rieger, M. (2010). ‘Apple (Malus domestica)’, in Introduction to Fruit Crops. New York, NY: Food Products Press, pp. 47-64.
Watkins, C.B. (2003). ‘Principles and Practices of Postharvest Handling and Stress’, in Ferree, D.C., Warrington, I.J. (ed.) Apples: botany, production, and uses. Cambridge, MA: CABI, pp. 585-614.
Westwood, M.Neil. (1993). ‘Dormancy and Plant Hardiness’, in Temperate-zone. Pomology. Physiology and Culture. Portland, Oregon: Timber Press, pp. 382-419.
Westwood, M.Neil. (1993). ‘Postharvest Storage and Nutritional Value’, in Temperate-zone. Pomology. Physiology and Culture. Portland, Oregon: Timber Press, pp. 336-363.
Кривко, Н.П. (2014). ‘Классификация плодовых растений [Classification of fruit plants]’, in Плодоводство [Fruit growing]. Санкт-Петербург: Лань, pp. 11-15.
Кривко, Н.П. (2014). ‘Обрезка и формирование кроны плодовых деревьев [Pruning and shaping the crown of fruit trees]’, in Плодоводство [Fruit growing]. Санкт-Петербург: Лань, pp. 125-157.
Кривко, Н.П. (2014). ‘Уход за молодым и плодоносящим садом [Caring for a young and fruitful garden]’, in Плодоводство [Fruit growing]. Санкт-Петербург: Лань, pp. 158-227.
Трунов, Ю.В., Самощенков, Е.Г., Дорошенко, Т.Н. (2012). ‘Биологические основы плодоводства [Biological foundations of fruit growing]’, in Плодоводство [Fruit growing]. Москва: КолосС, pp. 3-123.
Трунов, Ю.В., Самощенков, Е.Г., Дорошенко, Т.Н. (2012). ‘Семечковые культуры [Pome crops]’, in Плодоводство [Fruit growing]. Москва: КолосС, pp. 329-347.