Physiological disorders

How to Distinguish from Infectious Diseases and Pests?

This is a key question, and the answer lies in understanding the nature of the problem.

• Infectious Diseases (fungal, bacterial, viral):
• Causative Agent: There is always a pathogen (fungus, bacterium, virus) that is transmitted from plant to plant.
• Nature: They are contagious. Fungal spores or bacteria are spread by wind, rain, and insects.
• Manifestation: Often localized or focal in nature. Symptoms can be specific (e.g., spots with characteristic mold growth, cankers, gum exudation with signs of infection). Infections generally progress, moving from old leaves to young ones or spreading along branches.
• Examples: Moniliosis (brown rot), Coccomycosis, Bacterial Canker (Pseudomonas syringae).

• Physiological Disorders (Abiotic Stresses):
• Causative Agent: Absent. The cause is an imbalance of external or internal factors.
• Nature: Non-contagious. The problem will not spread from one tree to another unless conditions coincide.
• Manifestation: Often systemic or widespread. For example, uniform yellowing of leaves across the entire canopy due to chlorosis, fruit cracking after rain affecting many trees in the orchard, or frost damage on the south side of the trunk.
• Examples: Rain-induced fruit cracking (Knoche & Winkler, 2017), sunscald of bark, iron deficiency chlorosis, fruitlet drop due to drought (Agustí, 2010).

A Simple Test: If you see spots with clear boundaries, mold, or sporulation on leaves, with healthy tissue nearby — it's most likely an infection. If leaves are uniformly yellowing or drying at the edges, and all trees in the orchard look equally stressed after frost or drought — you are dealing with a physiological disorder.

Main Causes of Physiological Disorders

All causes can be grouped into several broad categories (Westwood, 1993):

1. Water Imbalance: Deficiency (drought, dry winds) or excess (waterlogging, over-irrigation) of moisture.

2. Mineral Nutrition Imbalance: Deficiency or, conversely, excess of one or more elements, leading to an imbalance.

3. Adverse Weather Conditions: Extreme temperatures (winter frosts, spring frosts, summer heat), sunburn, wind and hail damage.

4. Soil Problems: Inappropriate pH (especially high pH causing chlorosis), salinization, poor aeration (root respiration).

5. Agrotechnical Errors: Root damage during cultivation, improper pruning leading to gummosis, incompatibility between rootstock and scion.

Reversibility of Changes

This is one of the most critical questions for a gardener. Reversibility depends on the intensity and duration of the stress factor:

• Reversible Disorders: If the stress was short-lived and the cause is eliminated in time, the tree can fully recover. For example, leaves that wilted in the midday heat restore their turgor by evening. Buds damaged by a light frost may still produce a crop from lateral buds. A nutrient deficiency, when timely supplemented, eliminates chlorosis symptoms on new leaves.
• Partially Reversible: For example, bark damage from sunburn. The wound may heal over, but the affected tissue will not regenerate, and a scar will form in its place.
• Irreversible: Disorders that lead to tree death. For example, ring-like bark damage from frost or death of the root system during prolonged flooding. Seeds in fruits may be non-viable under severe stress, which, however, is not critical for the gardener growing varietal trees (Agustí, 2010).

Understanding the nature of physiological disorders is the first and most important step towards a healthy and productive orchard. In the following chapters, we will analyze in detail how to recognize and correct the most common problems.

2.1. Drought (Moisture Deficiency)

How to recognize? With prolonged water scarcity, leaves lose turgor, droop, and become dull. Leaf margins begin to yellow and dry (marginal burn). Shoot growth slows or stops. Fruits become smaller, less juicy, and with a sharp water deficit, massive fruitlet drop occurs (Agustí, 2010). In arid regions, if the water deficit is not replenished in time, the tree may enter a dormant state, shedding part of its foliage to survive.

Why does this happen? Water is essential for cell division and expansion. Moisture deficiency is particularly critical during phases of active fruit growth (Phase III — fruit swelling and ripening) and immediately after flowering. During this time, fruit cells are actively enlarging, and any water stress reduces their final size (Long et al., 2021). Furthermore, moisture evaporates through leaf stomata, creating a water flow from roots to the canopy. During drought, stomata close, photosynthesis slows down, and the tree cannot supply the fruits with carbohydrates.

What should a gardener do?

• Regular irrigation during critical periods: Be sure to water cherries during the phases: (1) immediately after flowering (for fruit set), (2) during fruit swelling (2-3 weeks before ripening), and (3) pre-winter (moisture-charging) irrigation in late autumn (after leaf fall) to prepare for winter.
• Mulching: A layer of organic mulch (straw, grass clippings, compost) 5–10 cm thick in the root zone conserves soil moisture, prevents root overheating, and reduces evaporation.
• Drip Irrigation: The most effective way to deliver water directly to the roots, especially in arid regions. It allows maintaining soil moisture at an optimal level without waterlogging.

2.2. Waterlogging and Root Flooding

How to recognize? Excess moisture in the soil is a more insidious enemy than drought. Signs include: leaves turning yellow and dropping prematurely, weak shoot growth. The tree appears stunted, and gummosis may be observed on the trunk. In severe cases (prolonged flooding), the bark at the root collar dies, and the tree perishes (Westwood, 1993).

Why does this happen? Water displaces oxygen from soil pores. Cherry roots (especially on vigorous rootstocks) are highly sensitive to oxygen starvation (asphyxia). In anaerobic conditions, root respiration is impaired; they cannot absorb water and nutrients. A favorable environment is created for the development of root rots (Phytophthora, Armillaria mellea), which are infectious diseases but are triggered precisely by waterlogging (Agustí, 2010). Additionally, in waterlogged soils, the availability of certain elements, especially iron, decreases, exacerbating chlorosis.

What should a gardener do?

• Choosing the right location: Do not plant cherries in low-lying areas where water stagnates or in sites with a high water table (less than 1.5–2 m from the surface).
• Drainage: If the site is prone to waterlogging, provide drainage ditches or plant trees on artificial mounds or raised ridges.
• Irrigate as needed: Do not water according to a calendar schedule; instead, monitor soil condition. Reduce irrigation during cool and rainy weather. Use moisture monitoring methods (e.g., a soil probe or a simple test: a handful of soil from a 20–30 cm depth should not crumble to dust, nor should it be as wet as clay).
• Soil cultivation: After heavy rains or irrigation, loosen the topsoil to break the crust and improve gas exchange.

2.3. Fruit Cracking (Rain-induced Cracking) — The Most Painful Result of Water Imbalance

This physiological disorder is a real scourge for cherry producers in many regions of the world (Knoche & Winkler, 2017).

How to recognize? A few days before harvest or just before it, after rain, cracks appear on the fruits. They can be slight — at the pedicel base or the stylar end (apical cracks), or deep, lateral cracks that split the fruit in half. Cracked fruits are unsuitable for sale and are quickly affected by rots. Even if cracks are not visible, rain causes microcracks in the cuticle, worsening the fruit's storage ability.

Why does this happen? Rainwater lands on the fruit and is absorbed through the skin. Inside the fruit, high osmotic pressure is generated by the sugars. Water enters the cells, they swell, and the skin, which can no longer stretch, bursts. However, there is a second mechanism: water is absorbed by the roots and transported to the fruit via the vascular system, causing internal pressure (Long et al., 2021). Cracking is exacerbated if a dry period is followed by sudden heavy rain, or if irrigation has been irregular. Susceptibility also depends on the variety (e.g., 'Bing' is very prone to cracking, while 'Regina' is more resistant) (Long et al., 2021; Knoche & Winkler, 2017).

What should a gardener do?

• Choosing resistant varieties: If your region experiences frequent rains during the ripening period, opt for relatively resistant varieties ('Regina', 'Kordia', 'Sweetheart' — the latter has moderate sensitivity) (Long et al., 2021; Mandal et al., 2021).
• Regular irrigation: Maintain stable soil moisture. Avoid sharp fluctuations: overly dry soil followed by abundant irrigation or rain. This significantly reduces the risk of cracking (Long et al., 2021).
• Calcium sprays: Pre-harvest (3–4 weeks before harvest) and post-harvest applications of calcium chelate or calcium chloride strengthen cell walls and reduce skin sensitivity to cracking. Calcium also improves fruit storage life (Long et al., 2021).
• Rain covers (only for small forms): In hobby gardens or small farms, plastic covers (tents) can be used over individual trees to protect fruits from precipitation during the critical period. This is expensive but effective (Knoche & Winkler, 2017).

Important: Cracking is not an infection but a purely physical disorder. Fungal infections typically follow, entering through the damaged skin; therefore, preventing cracking is also a preventive measure against rots.

3.1. Nutrient Deficiencies

Nitrogen (N) Deficiency

• How to recognize? Nitrogen is the growth element. With its deficiency, leaves become pale green or yellow (chlorosis), starting with older, lower leaves, as nitrogen is mobilized and moves to young tissues. Shoot growth is weak and spindly. Flowering and fruiting may be abundant, but fruits are small, and yield decreases. In severe cases, leaves drop prematurely (Long et al., 2021).
• Why does this happen? Nitrogen is a key component of chlorophyll, proteins, and enzymes. Its deficiency is especially critical in spring during active shoot and leaf growth. In cold, rainy springs, root absorption of nitrogen slows down, which can cause temporary starvation even on fertilized soils.
• What should a gardener do? In early spring, before bud break, apply nitrogen fertilizers (urea, ammonium nitrate) in the root zone (40–60 g per 1 m² of canopy projection) (Agustí, 2010). During fruit growth (second half of June — early July), you can apply a foliar feed (spraying leaves) with a weak urea solution (0.5%). Important: nitrogen excess in the second half of summer is dangerous — it provokes late shoot growth, which does not mature in time and freezes in winter.

Phosphorus (P) Deficiency

• How to recognize? Phosphorus deficiency is rarer but manifests characteristically: leaves become dark green with a bluish or bronze tint, leaf margins may roll upward. Shoot growth is slow, shoots are thin. Flowering and fruit ripening are delayed (Long et al., 2021).
• Why does this happen? Phosphorus participates in energy metabolism (ATP) and cell division. It is immobile in the soil and poorly absorbed at low temperatures or in acidic soils.
• What should a gardener do? Apply phosphorus fertilizers (superphosphate, double superphosphate) in autumn or spring, incorporating them into the soil at root depth (15–20 cm). On acidic soils (pH < 5.5), phosphorus binds into unavailable forms, so prior liming is necessary.

Potassium (K) Deficiency

• How to recognize? This is one of the most common deficiencies in stone fruits. Symptoms: margins and tips of older leaves turn yellow, then brown and die (marginal burn). Leaves may curl upward. Fruits become smaller, softer, crack easily, and store poorly (Long et al., 2021).
• Why does this happen? Potassium is the "pump" for transporting water and carbohydrates. It is critically important for fruit swelling and quality. Due to the removal of potassium with the harvest, its deficiency increases towards the end of summer. It is particularly common on light sandy soils.
• What should a gardener do? Apply potassium fertilizers (potassium sulfate, potassium salt) during autumn digging or in spring. A summer potassium feed during the fruit growth phase (0.5–1% solution by foliar spray) is effective. Remember the competition with calcium and magnesium: excess potassium can induce their deficiencies.

Calcium (Ca) Deficiency

• How to recognize? Symptoms: young leaves become deformed, their margins curl upward, chlorotic spots appear, which then die off. Internodes shorten. Calcium is especially important for fruits: its deficiency makes the skin thin, reduces shelf life, and lowers resistance to cracking (Long et al., 2021; Knoche & Winkler, 2017).
• Why does this happen? Calcium is a structural element of cell walls. It is immobile in the plant and poorly transported to fruits when there is high competition with potassium or magnesium.
• What should a gardener do? Apply calcium to the soil (dolomite lime, gypsum, calcium nitrate) or conduct regular foliar feeds with calcium chelate (0.3–0.5%) during fruit growth, starting from the pit-hardening stage (Long et al., 2021).

Iron (Fe) Deficiency

• How to recognize? Iron chlorosis is a scourge of many fruit orchards. Leaves turn yellow (become chlorotic), but the veins remain bright green. Symptoms appear first on the youngest leaves. With severe deficiency, leaves turn white and die (Long et al., 2021).
• Why does this happen? The most common cause is not a lack of iron in the soil, but its unavailability due to high pH (alkaline soils > 7.0) or excess lime. Iron is also poorly absorbed in cold, wet weather.
• What should a gardener do? This is one of the most challenging problems. A temporary measure is foliar spraying with an iron chelate solution (e.g., Ferrovit). However, the fundamental solution is lowering soil pH: applying sulfur, acidic fertilizers (ammonium nitrate), mulching with acidic peat. Choosing resistant rootstocks is also important (Long et al., 2021).

Boron (B) Deficiency

• How to recognize? Boron is a crucial micronutrient for flowering and fruiting. Its deficiency causes: poor flowering, massive fruitlet drop, fruit deformation, and dieback of shoot tips (tip burn). Chlorotic spots may appear on leaves (Long et al., 2021).
• Why does this happen? Boron is not easily mobile; its deficiency often occurs on light, sandy soils.
• What should a gardener do? Apply boron (0.1–0.2% boric acid or borax solution) during the flowering phase and during fruitlet growth. Spraying should be done in the morning or evening hours.

3.2. Element Excess and Imbalance

Excess is as harmful as deficiency.

• Nitrogen excess: Causes vegetative vigor — excessive leaf growth at the expense of flowering and fruiting. Shoots become thick but soft, mature poorly, and suffer more from frost. The tree becomes more vulnerable to powdery mildew and bacterial canker.
• Potassium excess: Inhibits calcium and magnesium absorption, manifesting as symptoms of their deficiencies (small fruits, brittle shoots, leaf scorch, chlorosis).
• Calcium excess (on alkaline soils): Blocks the availability of iron, zinc, and manganese, causing chlorosis.

3.3. What should a gardener do: Nutritional Balance

• Fertilize wisely. Use complex fertilizers with micronutrients (in chelated form for better absorption). Follow recommendations: for cherries, depending on yield, recommended doses are Nitrogen 80–100 kg/ha/year (active ingredient basis), Phosphorus 50–70 kg/ha, Potassium 100–120 kg/ha (Agustí, 2010). For a hobby garden, this translates roughly to: 40–60 g N, 30–50 g P, 60–80 g K per 1 m² of feeding area.
• Regular soil and leaf analysis. This provides an accurate picture and allows for adjustments in fertilization.
• Liming (reducing acidity). On acidic soils (pH < 6.0), apply lime or dolomite flour (every 3–4 years), as in acidic environments many elements become less available. But remember, on excessively limed soils (pH > 7.5), chlorosis occurs.
• Mulching and organic matter. Applying organic fertilizers (compost, humus) improves soil structure and its buffering capacity, maintaining optimal pH and providing plants with nutrients in a balanced form.

4.1. Frost Damage (Winter and Spring)

Frost is the main limiting factor for growing cherries in many regions. Damage can vary depending on the season and the tree's developmental stage (Westwood, 1993; Wenden et al., 2017).

How to recognize?

• Winter damage to wood and bark: Longitudinal cracks (frost cracks) appear on the trunk and main branches; bark peels off. On a cross-section of a branch, darkening (browning) of the wood or cambium is visible. Ring-like bark damage is most dangerous, leading to the tree's death above the damaged area. The southwest side of the trunk (especially on young trees) is often affected due to sharp temperature fluctuations: the bark heats up in the sun during the day and cools rapidly at night (sun-scald frost injuries).
• Damage to flower buds: This is the biggest problem for the harvest. Buds that have started to grow lose their frost hardiness. During return frosts, flowers and fruit sets darken, become glassy, turn brown, and drop. Inside the buds, blackened pistils and stamens can be seen. The critical temperature for flowering cherries is about -2°C to -3°C, with up to 90% of flowers killed (Wenden et al., 2017).
• Frost cracks on bark: After severe winter frosts, the bark may crack, exposing the wood. These wounds are open gates for infections.

Why does this happen?

• Wood: During rapid cooling, moisture in the cells freezes, forming ice crystals that rupture cell membranes. The cambium — the thin layer of dividing cells responsible for growth in thickness — is particularly vulnerable.
• Flower buds: Exiting dormancy (endodormancy) and the onset of growth make them extremely sensitive to negative temperatures. The more developed the bud, the lower its frost hardiness. Ice-nucleating bacteria play an important role; they accelerate ice formation in tissues at higher temperatures (Westwood, 1993).

What should a gardener do?

• Proper site selection: Avoid low-lying areas and closed basins where cold air accumulates (frost pockets). Choose sites with good air circulation (slopes, elevated areas).
• Selection of varieties and rootstocks: Choose regionally adapted varieties with high winter hardiness of wood and flower buds. Rootstocks from Prunus mahaleb (Mahaleb cherry) are generally hardier than those from Prunus avium (sweet cherry) (Westwood, 1993). Pay attention to flowering time: late-flowering varieties ('Regina', 'Kordia') often avoid spring frosts.
• Protecting trunks from sun-scald frost injury: In autumn or late winter (during a thaw), whitewash trunks and bases of main branches with garden paint or water-based paint with copper sulfate added. This reflects sunlight and prevents the bark from overheating during the day.
• Protection against spring frosts (for small areas): During flowering, monitor the weather forecast. If frost is threatened:
• Sprinkler irrigation: Fine mist spraying of the canopy with water at night before the frost. Freezing water releases heat that protects the flowers. Important: start the system before the frost arrives and do not turn it off until dawn.
• Smudging: Making smoke piles (from damp straw, sawdust, leaves) on the windward side of the orchard. Smoke creates a "blanket" that reduces radiative cooling of the soil.
• Covering: Young or small trees can be covered with spunbond or agro-fabric.

4.2. Heat and Sunburn

Summer heat can cause no less damage, especially in southern regions. Cherry is sensitive to high temperatures, particularly during fruit ripening and flower bud differentiation for the next year.

How to recognize?

• Sunburn of bark and fruits: On the south side of the bark, areas of dead tissue appear; bark cracks and peels. On fruits — depressed, light-colored, dry spots (necroses); the flesh beneath them becomes bitter and dry. Fruits lose marketable quality.
• Flower bud damage (formation of double fruits): If temperatures exceed 30 °C during the period of flower bud differentiation (usually 3–4 weeks after harvest, in July-August), it causes developmental anomalies: formation of double pistils, leading to fused, misshapen fruits (double fruits) the following year (Wenden et al., 2017; Quero-García et al., 2017).
• Fruit sunburn (sunburn): Direct sunlight combined with high temperatures (above 40 °C) causes skin burn. Fruits become soft, lose turgor, and develop brown, sunken spots (Long et al., 2021).

Why does this happen?

• Bark and fruits: High temperature causes protein denaturation and cell death. Parts not adapted to direct sunlight (e.g., bark previously shaded by foliage and then exposed after pruning) are particularly affected.
• Double fruits: High temperature disrupts the normal process of flower bud differentiation, leading to the formation of two pistils instead of one. Varietal susceptibility varies greatly: for example, 'Bing' is very sensitive, while 'Regina' is more resistant (Wenden et al., 2017).

What should a gardener do?

• Bark protection: Whitewashing trunks in spring and autumn (as for frost protection). This is especially important for young trees with thin bark.
• Fruit and bud protection:
• Irrigation (sprinkling): On hot days, you can perform refreshing canopy sprinkling in the morning or evening. Evaporating water cools the leaves and fruits.
• Mulching: A layer of organic mulch (straw, grass clippings) protects the soil from overheating and retains moisture, indirectly reducing heat stress on the tree.
• Use of shade nets (for intensive orchards): In commercial horticulture, special shade nets (15–20% shading) are used to reduce fruit temperature and prevent sunburn.
• Choosing resistant varieties: If your region has hot summers, choose varieties less prone to forming double fruits ('Lapins', 'Sweetheart' — moderate sensitivity) (Wenden et al., 2017).

4.3. Air Pollution

This issue is relevant for orchards located near industrial zones, highways, or large cities. The main pollutants are ozone and nitrogen oxides (NOx).

How to recognize? Small necrotic spots (stippling), mottling, premature yellowing, and leaf drop appear on leaves. Young leaves may become deformed. In severe cases, general tree decline, reduced growth, and lower yields are observed. Symptoms often resemble fungal diseases but, unlike them, appear across the canopy and lack the characteristic mold growth.

Why does this happen? Ozone and other oxides are powerful oxidants. They damage cell membranes, disrupting photosynthesis and respiration. Toxic oxidation products accumulate over time with prolonged exposure.

What should a gardener do? Unfortunately, there are no effective protective measures for hobby gardens. The primary solution is choosing a planting site away from pollution sources. It is also important to keep the tree in good condition: adequate nutrition and watering increase its resistance to stress.

4.4. Salt Stress (Soil Salinization)

In arid regions, when using irrigation water with high salt content (especially sodium and chloride), or on naturally saline soils, cherries may suffer from salt stress (Machado & Serralheiro, 2020).

How to recognize? Leaf margins yellow, then brown and die (marginal burn). Shoot growth is severely stunted. In severe cases, leaves drop, and branches die back. Brown spots may appear on fruits. Cherry, like most stone fruits, is considered salt-sensitive (Machado & Serralheiro, 2020).

Why does this happen?

• Osmotic effect: High salt concentration in the soil solution hinders root water uptake, causing physiological drought.
• Ion toxicity: Sodium and chloride ions accumulate in tissues, disrupting enzymatic processes. Chlorine is particularly dangerous, inhibiting photosynthesis and causing leaf burn.
• Mineral nutrition disruption: Excess sodium in the soil blocks calcium and potassium uptake, exacerbating their deficiencies.

What should a gardener do?

• Water analysis: Before using water for irrigation, check its electrical conductivity (EC). For cherries, the critical salinity threshold for irrigation water is about 1.5–2.0 dS/m (Machado & Serralheiro, 2020).
• Soil leaching: Applying increased amounts of irrigation water to leach salts from the root zone (provided there is drainage). Use water with low mineralization for irrigation.
• Applying organic fertilizers: Compost or humus improves soil structure and binds toxic ions.
• Using gypsum (CaSO4): Gypsum displaces sodium from the soil exchange complex, making it leachable.
• Selecting tolerant rootstocks: Some rootstocks (e.g., Gisela 5, Gisela 6) may be more tolerant to salt stress than others (Long et al., 2021).

5.1. Flower and Fruitlet Drop (Physiological Drop)

How to recognize? The cherry blooms profusely, but after some time (1–3 weeks after flowering), some flowers and later small fruitlets drop. This is a natural self-regulating process — the tree sheds excess fruits it cannot "feed." However, if more than 80–90% of fruitlets drop, it becomes a problem. Difference from diseases: during physiological drop, healthy, spotless, and rot-free fruitlets fall. With Moniliosis, for example, flowers turn brown, develop gray mold, and dry up without falling (Agustí, 2010; Long et al., 2021).

Why does this happen? The primary cause is a lack of carbohydrates (sugars) to feed the growing fruitlets. Early in fruit development (Phase I — cell division), it requires a lot of energy. If the tree is weakened by drought, waterlogging, nitrogen or phosphorus deficiency, or if it has too many fruits (overcropping), photosynthesis cannot meet the demand. Drop can also be caused by poor pollination (lack of bees, cold weather during flowering) — then fruitlets simply are not fertilized and do not develop (Agustí, 2010). Hormonal imbalance (drop in auxin levels and increase in abscisic acid) also plays a role.

What should a gardener do?

• Ensure good pollination. Plant several varieties for cross-pollination (if the variety is self-sterile). Attract bees: plant nectar sources nearby, do not use insecticides during flowering.
• Balanced nutrition. Nitrogen is particularly important in early spring, but without overfeeding. Apply a complex fertilizer with a higher proportion of phosphorus and potassium before flowering.
• Irrigation. Do not allow the soil to dry out during flowering and immediately after (fruit set phase).
• Fruit thinning. If the yield was very high the previous year, the tree may have depleted its reserves. This year, manual thinning (removing excess fruitlets) may be needed to reduce competition.

5.2. Fruit Smallness (Small Fruit Size)

How to recognize? Fruits are noticeably smaller than they should be for the variety, even with good color. The flesh may be less juicy, and the pit larger relative to the flesh.

Why does this happen? A key reason is overcropping. When there are too many fruitlets, they compete for carbohydrates and water. As a result, no single fruit reaches its size potential (Agustí, 2010; Long et al., 2021). A second reason is water deficiency during the fruit swelling phase (Phase III — from late June to harvest). A third is a lack of potassium and calcium, which are necessary for cell growth. Lack of light (dense canopy) also plays a role.

What should a gardener do?

• Crop load management. Remove some fruitlets manually or with chemical thinners (e.g., NAA — naphthaleneacetic acid, but manual thinning is better for hobbyists). Leave no more than 2–3 fruits per fruiting spur.
• Regular irrigation. Water during dry weather, especially during fruit growth.
• Potassium and calcium fertilization. Foliar applications of potassium sulfate (1%) and calcium chelate (0.3%) during fruit growth improve size and quality.
• Pruning. Remove excess, crowding branches to improve fruit illumination.

5.3. Uneven Fruit Ripening

How to recognize? On a single tree, fruits ripen at different times: some are already dark red and sweet, others are still green or yellow. This can prolong harvest and reduce its overall quality.

Why does this happen? This is most often related to uneven distribution of light and nutrients within the canopy. Fruits on well-exposed outer branches ripen earlier. It can also be caused by uneven watering (alternating drought and abundance), leading to different growth rates. Some varieties are genetically predisposed to extended ripening (e.g., 'Sweetheart' ripens gradually) (Buckingham, 2010).

What should a gardener do?

• Proper pruning. Ensure uniform illumination of the entire canopy by removing vertical shoots (water sprouts) and crowding branches.
• Uniform irrigation. Keep the soil in a consistently moist state (without overwatering) during ripening.
• Variety selection. If uniform harvest timing is important to you, choose varieties with synchronized ripening (e.g., 'Bing', 'Lapins').

5.4. Gummosis of Physiological Origin

How to recognize? On the trunk, main branches, or at the graft union, drops or masses of amber, resinous liquid appear. This is the tree "weeping."

Why does this happen? Gummosis is a defensive reaction of the tree to injury. It can be caused by infections (bacterial canker, Pseudomonas syringae — then gum exudes from sharply defined cankers), but often has a physiological nature: mechanical damage to the bark (from hail, tools, rodents), frost cracks (especially on the southwest side), sunburn, root waterlogging or sharp moisture fluctuations, as well as rootstock-scion incompatibility (Westwood, 1993; Webster & Looney, 1996). Physiological gummosis, unlike infectious, is not accompanied by typical cankers or cambial dieback around the wound, but its presence weakens the tree and opens gates for infections.

What should a gardener do?

• Prevent damage. Handle bark gently during pruning, seal fresh cuts with grafting wax or oil paint. Protect trunks from rodents (netting, wrapping) and sunburn (whitewashing).
• Drainage. Eliminate root waterlogging.
• Wound treatment. If gum has already appeared, carefully clean the wound with a sharp knife down to healthy wood, treat with a 1% copper sulfate solution, and seal with grafting wax.
• Select compatible rootstocks. When planting, use only proven, compatible scion-rootstock combinations (e.g., for sweet cherries good rootstocks are Gisela 5, Gisela 6, MaxMa 14; for sour cherries, Mahaleb).

5.5. Yield Decline (General Tree Weakening)

How to recognize? The tree produces fewer and fewer fruits each year, shoot growth is weak, the canopy is sparse. Leaves become smaller and lighter. This is often the result of a combination of several stresses rather than a single cause.

Why does this happen? Causes can be multiple: long-term under-supply of nutrients (especially potassium and phosphorus), drought, waterlogging, root or trunk damage, improper pruning (exposing branches), tree aging, soil depletion. Also, biennial bearing (alternate bearing) — when a high-yield year is followed by a low-yield one, becomes the physiological norm for some varieties, but if the tree is weakened, it can lead to total crop failure.

What should a gardener do?

• Comprehensive care. Regularly (every 3–4 years) conduct agrochemical soil analysis and adjust fertilization.
• Soil improvement. Add organic matter (compost, humus) to restore fertility and structure.
• Rejuvenating pruning. Remove old, unproductive branches to stimulate new shoot growth.
• Weed control. Keep the root zone free of weeds that compete for moisture and nutrients.
• Root system restoration. If the tree suffers from soil compaction, perform deep cultivation or aeration (puncturing) of the soil in the root zone.

Conclusion for the chapter: Disorders of growth and fruiting are often signals that the tree lacks strength. Unlike diseases, there is no pathogen involved, and treatment comes down to improved care. Carefully analyze the tree's condition, and you will be able to adjust watering, fertilization, and pruning in time, restoring the cherry's health and high productivity.

6.1. Optimal Agrotechnics — The Foundation of Health

The basis of prevention is proper care throughout the tree's life cycle. There are no small details: from choosing the planting site to autumn pruning — everything matters.

1. Correct Site and Variety Selection:

• Site: Plant cherries on well-drained, light loams or sandy loams with a neutral reaction (pH 6.5–7.0). Avoid low-lying areas with stagnant cold air and high groundwater levels (Westwood, 1993). For southern regions with hot summers, choose sites protected from midday sun.
• Variety: Choose regionally adapted varieties suitable for your climate. Consider not only fruit taste but also resistance to cracking ('Regina', 'Kordia'), frost hardiness of flower buds, and susceptibility to double fruit formation (Long et al., 2021; Wenden et al., 2017). For regions with cold winters, varieties on winter-hardy rootstocks (Prunus mahaleb) are preferred.

2. Rational Irrigation (Key to Water Balance):

• Schedule: Water regularly, especially during critical phases: (1) immediately after flowering (for fruit set), (2) during fruit swelling (3–4 weeks before harvest), (3) pre-winter moisture-charging irrigation in late autumn (after leaf fall).
• Depth: Water abundantly, ensuring moisture penetrates the root zone (30–50 cm). Surface watering encourages roots to grow in the upper layer, which dries out quickly.
• Consistency: Avoid sharp moisture fluctuations (from dry to wet). This is the primary cause of fruit cracking. Use drip irrigation or mulching to maintain stable moisture (Long et al., 2021).
• Drainage: On heavy clay soils, ensure excess water is drained. Cherry roots cannot tolerate waterlogging — it leads to oxygen starvation, chlorosis, and root death.

3. Balanced Nutrition:

• Regular analysis: Conduct agrochemical soil analysis and leaf diagnostics (every 2–3 years) to accurately determine tree needs (Long et al., 2021).
• Basic fertilization: In spring (before bud break), apply nitrogen (30–40% of the annual rate), phosphorus, and potassium according to analysis results. In summer (during fruit growth), focus on potassium and calcium (foliar feeds) to improve fruit quality and resistance to cracking.
• Micronutrients: Regularly (every 2–3 weeks during the growing season) apply foliar feeds with chelated forms of iron, zinc, boron, and manganese, especially on alkaline soils where these elements are poorly absorbed.
• Organic matter: Apply well-rotted manure, compost, or humus during autumn digging (every 2–3 years). Organic matter improves soil structure, its buffering capacity, and supplies the tree with micronutrients in available form.

4. Correct Pruning and Canopy Formation:

• Purpose: Create an open, well-lit canopy so all fruits receive enough light and air. This reduces the risk of sunburn, improves fruit quality and color.
• Timing: Perform major pruning in early spring (before sap flow) so wounds heal faster. Summer pruning (pinching) is used to restrict growth and stimulate fruiting.
• Sanitary pruning: Regularly remove dry, broken, and diseased branches. Seal all cuts larger than 1 cm in diameter with grafting wax to prevent gummosis and infections.

6.2. Regular Monitoring of Tree Condition

Prevention is impossible without careful observation of the tree. Regular inspection is your primary tool for early diagnosis.

What to check and when:

• Spring (bud swell — flowering): Assess the condition of flower buds after winter (have they darkened inside?). Monitor frost forecasts and be prepared for protective measures (sprinkling, smoking). Assess the abundance of flowering — this will indicate if fruit thinning will be needed.
• Early Summer (shoot and fruitlet growth): Check shoot growth (should be 30–50 cm). If growth is weak — there may be a lack of nitrogen or moisture. Monitor for chlorosis (leaf yellowing with green veins) — a sign of iron deficiency or soil pH problems.
• Mid-Summer (fruit swelling): This is the most critical time for soil moisture control and regular potassium and calcium fertilization. Assess fruit size and color. Appearance of cracks signals irrigation instability.
• Autumn (after harvest): Assess the overall tree condition, presence of gummosis, bark damage. Perform sanitary pruning and moisture-charging irrigation. Apply phosphorus-potassium fertilizers to prepare for winter.
• Winter: Protect trunks from rodents (wrapping, netting) and sunburn (whitewashing). In regions with little snow, cover the root zone with mulch to protect roots from freezing.

6.3. Preventing Stress Factors

Since many disorders are caused by extreme conditions, your task is to mitigate their impact.

• Frost protection: Choose frost-resistant varieties. Whitewashing trunks is mandatory. To protect flowers from spring frosts, use sprinkler irrigation (start the system before the frost arrives and until dawn) or cover with non-woven fabric. In commercial orchards, wind machines or heaters are used (Westwood, 1993).
• Heat and sun protection: In hot climates, use shade nets (15–20% shading) during fruit ripening and flower bud differentiation (July-August) to reduce temperature and prevent double fruit formation (Wenden et al., 2017). Regular watering and mulching also help reduce heat stress.
• Wind protection: In regions with strong winds, create windbreaks or use windbreak screens to reduce mechanical damage to fruits and leaves and to decrease moisture evaporation.
• Salinity protection: If using irrigation water with high salt content, practice leaching irrigation to wash salts from the root zone, apply gypsum and organic matter, and choose more salt-tolerant rootstocks (e.g., from Prunus mahaleb).

Conclusion

Physiological disorders are not a death sentence but a signal that the tree needs your help. Unlike infectious diseases, they are not contagious and are generally reversible. The key to preventing them lies in creating the most comfortable conditions for the cherry: proper irrigation, balanced nutrition, protection from extreme temperatures, and regular, attentive care. Remember: a healthy, vigorous tree is much better equipped to withstand both abiotic and biotic stresses (diseases and pests).

Observe your trees, learn to understand their language — and they will reward you with abundant harvests of delicious and beautiful fruits!