Physiological disorders

Why Do Physiological Disorders Occur?

Cucumber is a crop that evolved in the humid tropics of India (Wien & Stützel, 2020). Its genetic programme is adapted to consistently warm, humid conditions with mild temperature fluctuations. When we try to grow cucumbers in regions with cold nights, hot summers or erratic irrigation, the plant experiences stress and responds with growth, flowering and fruiting disorders.

The main groups of stress factors causing physiological disorders:

1. Temperature stresses – cold, overheating, sharp fluctuations

2. Water stresses – drought, waterlogging, uneven irrigation

3. Nutritional disorders – deficiency, excess or imbalance of elements

4. Light conditions – insufficient or excessive lighting

It is important to understand that these factors rarely act in isolation. For example, cold soil reduces the roots' ability to absorb phosphorus and other elements, leading to a complex nutritional disorder against a background of temperature stress. Therefore, diagnosing physiological disorders requires careful observation of all growing conditions.

How to Distinguish Physiological Disorders from Diseases

Some symptoms can be similar: for example, wilting due to Fusarium and wilting due to root overheating. However, with physiological wilting, turgor is restored in the evening or after watering, while with Fusarium it is not (Akhatov et al., 2013).

Why Is It Important to Distinguish?

The most common mistake made by gardeners is to immediately look for a disease and apply fungicides when any plant problem appears. This is not only useless for physiological disorders but can also be harmful: chemicals create additional stress for weakened plants, suppress beneficial microflora, and increase the load on plants (Mondal et al., 2020).

Physiological disorders are a signal that the plant sends to the gardener: “something is wrong with my conditions.” The gardener's task is to read this signal correctly and correct the conditions, rather than treat the plant for a non‑existent disease.

Practical Takeaways

• When a problem is detected, first assess the growing conditions: soil and air temperature, irrigation regime, fertilisation schedule
• Determine the scale of the problem: if the disorder is widespread and uniform, it is most likely a physiological stress
• If symptoms do not disappear within 5–7 days after correcting the conditions, then consider the possibility of an infectious disease and conduct diagnostics

In the following chapters we will discuss specific physiological disorders – grouped by stress factors – and explain in detail how to recognise them and what to do in each case.

2.1. Cold Soil

Symptoms. Plants look depressed: growth slows down or stops completely, leaves become dark green with a bluish tint, sometimes yellowing. With a sudden cold snap, wilting occurs even in moist soil – turgor does not recover by evening. Roots acquire a brownish tint and may rot (Akhatov et al., 2013; Tarakanov & Mukhin, 2003).

Why it happens. When soil temperature drops below +16 °C, cucumber roots lose the ability to actively absorb water and mineral elements – especially phosphorus. Water enters the plant more slowly than it evaporates from leaves, hence wilting. In addition, soil pathogens (Pythium, Fusarium) become sharply activated in cold soil and attack weakened roots (Wien & Stützel, 2020). As a result, the plant not only starves but also suffers from root rots that would not be a threat in warm soil.

What to do.

• Plant seedlings only in warmed soil. The minimum temperature at a depth of 10 cm should be no lower than +15 °C. In the temperate zone this is usually late May – early June. Dark mulch, raised beds and plastic covers help accelerate warming.
• Water only with warm water. Water from a well or borehole should be allowed to stand and warm up to +20…+22 °C. Cold watering is one of the main causes of root stress (Tarakanov & Mukhin, 2003).
• Mulch the soil. Organic mulch (straw, compost, mowed grass) retains heat, prevents sharp temperature fluctuations and protects roots from overcooling during cold nights.
• Use cold‑tolerant varieties and hybrids. Breeders have developed lines capable of germinating and growing at lower temperatures. For example, cucumber has cold‑tolerance genes (including cytoplasmic ones), and modern hybrids for open ground are significantly more resistant to cold than old varieties (Wehner et al., 2020).

2.2. Cold Nights

Symptoms. Plants look normal during the day, but in the morning leaves droop, their edges may turn yellow or dry out. Ovaries turn yellow and drop, and those that remain often produce deformed fruits – thickened near the stalk or with “constrictions”. Flowering becomes sparse, with male flowers (empty flowers) dominating (Mondal et al., 2020; Wien & Stützel, 2020).

Why it happens. Cucumber needs not only an average temperature but also a certain night‑time minimum for normal development. At night temperatures below +16 °C, cell division in the ovaries slows down, assimilate transport from leaves to fruits is disrupted, and pollen becomes sterile – pollination does not occur and ovaries drop (Wien & Stützel, 2020). Moreover, fruit growth occurs mainly at night, and cold inhibits this process.

What to do.

• Cover plants at night. In open ground use non‑woven fabric (spunbond, lutrasil) – it adds 2–4 °C. In greenhouses, avoid a sharp temperature drop after evening ventilation.
• Use warm beds. In northern regions, “steam” beds with manure or compost placed at the base are used; as they decompose, they release heat and warm the soil (Tarakanov & Mukhin, 2003).
• Choose planting dates correctly. In regions with cold nights, it is better to plant seedlings 1–2 weeks later but in consistently warm weather, rather than risk early planting.

2.3. Overheating (High Temperatures)

Symptoms. Leaves become pale, yellow at the edges, edges curl upward (a sign of scorch). Plants wilt even with sufficient watering. Flowers and ovaries drop en masse, fruits become smaller and bitterness appears. In intense heat (above +35 °C), pollen becomes sterile and ovaries do not form at all (Mondal et al., 2020; Wehner et al., 2020).

Why it happens. At temperatures above +32 °C, photosynthetic enzyme function is disrupted, and at +35…+38 °C chlorophyll is damaged. The plant spends more energy on respiration than it gains from photosynthesis. Pollen and ovaries suffer particularly: pollen grains lose viability, and pollination becomes impossible. In addition, overheating increases transpiration, and the plant cannot replenish water loss even if the soil is moist (Wien & Stützel, 2020).

What to do.

• Shade the plants. During hot midday hours, use shading nets (30–50% shade). In greenhouses, whitewash glass or film with chalk solution. In open ground, intercrop with tall plants (corn, sunflower) that create light shade (Tarakanov & Mukhin, 2003).
• Humidify the air. Sprinkling (refreshing irrigation) – spraying plants and air in hot weather – lowers leaf temperature by 5–8 °C through evaporation. Water consumption – 50–80 m³/ha – does not replace root watering but helps during midday heat (Tarakanov & Mukhin, 2003).
• Water regularly and abundantly. In hot weather, cucumber consumes up to 10 litres of water per day per mature plant (Wien & Stützel, 2020). Watering should be deep and done early morning or evening.
• Choose heat‑tolerant varieties. There are hybrids that withstand high temperatures better, e.g., for southern regions (Wehner et al., 2020).

2.4. Sharp Temperature Fluctuations

Symptoms. Fruits acquire ugly shapes – “hook‑shaped”, curvature, constrictions (see Chapter 6). Mass abortion of ovaries occurs, leaves may curl and develop chlorotic spots. Plants look “confused” – young green leaves and yellowed old ones may appear simultaneously (Mondal et al., 2020; Akhatov et al., 2013).

Why it happens. Cucumber does not like sharp contrasts. A day‑night temperature difference of more than 10–12 °C causes stress, disrupts hormonal balance and assimilate transport. Such swings are especially dangerous during fruiting – they lead to uneven fruit growth because cells divide and grow quickly on warm days, while growth slows on cold nights. As a result, the fruit develops unevenly and often becomes deformed (Wien & Stützel, 2020).

What to do.

• Try to smooth out fluctuations. In greenhouses, use heat accumulation systems (water containers, dark surfaces that store daytime heat and release it at night). In open ground, cover material helps reduce night cooling.
• Ventilate greenhouses properly. Open vents gradually to avoid sharp drafts and temperature changes.
• Maintain stable watering. Moist soil cools more slowly at night and warms more slowly during the day, acting as a temperature buffer.

Brief Summary of Temperature Disorders

The main principle. Cucumber is not a capricious but a signalling plant. Any temperature deviation from its comfort zone is reflected in its appearance. The gardener's task is to notice these signals in time and promptly adjust conditions, before stress becomes irreversible.

3.1. Water Deficit (Drought)

Symptoms. During the day, plants lose turgor – leaves droop and become limp, even if they looked healthy in the morning. Leaf edges dry out and curl upward. Fruits become small, coarse, and develop a characteristic bitterness (see Chapter 6). Flowering shifts towards male flowers (empty flowers), and ovaries that do form often drop (Mondal et al., 2020; Tarakanov & Mukhin, 2003).

Why it happens. When soil water is lacking, roots cannot supply transpiration – evaporation from leaf surfaces. The plant closes stomata to reduce water loss, but this stops carbon dioxide uptake and photosynthesis. In addition, under water deficit the plant synthesises abscisic acid – a stress hormone that inhibits fruit growth and promotes leaf senescence. Pollination also suffers: pollen becomes less viable, and even pollinated ovaries do not receive enough assimilates for growth. It is precisely under drought conditions that cucurbitacin – the substance that gives bitterness – accumulates in fruits (Mondal et al., 2020; Wien & Stützel, 2020).

What to do.

• Water deeply and infrequently, rather than often and superficially. With surface watering, water does not reach the bulk of roots, and the plant still suffers drought. Optimal watering is to wet the soil layer to a depth of 25–30 cm.
• Water in the morning or evening. Watering at noon leads to large evaporation losses and can cause leaf burn. Morning watering allows the plant to store moisture for the hot day; evening watering restores turgor after daytime stress.
• Mulch the soil. A layer of mulch (straw, mowed grass, compost, dark film) reduces evaporation from the soil surface, reduces overheating of the root zone and conserves moisture. In hot weather, mulch reduces watering needs by 20–30%.
• Monitor soil moisture. A simple test: squeeze a lump of soil from a depth of 10–15 cm in your fist. If the lump crumbles – it is time to water. Optimal moisture for cucumber is about 80% of full water‑holding capacity (Tarakanov & Mukhin, 2003).

3.2. Waterlogging (Flooding)

Symptoms. Leaves become dark green with a bluish tint, then start yellowing and falling off. Plant growth stops, ovaries drop en masse. Roots darken, turn brown and rot – an unpleasant odour appears from the soil. With prolonged flooding (more than 2–3 days), plants may die (Mondal et al., 2020; Wien & Stützel, 2020).

Why it happens. Cucumber roots need oxygen for respiration. In waterlogged soil, all pores are filled with water, and oxygen availability drops sharply. Under anaerobic conditions, root cells switch to alcoholic fermentation, releasing toxic products (ethanol, acetaldehyde) that kill root hairs and cause root death. Damaged roots become easy prey for soil pathogens – Pythium, Fusarium, Rhizoctonia (Akhatov et al., 2013). In addition, under anaerobic conditions, uptake of potassium, calcium and magnesium is impaired, exacerbating stress.

Especially important: cucumber reacts critically even to short‑term (1–2 days) flooding – roots begin to die within 12 hours (Tarakanov & Mukhin, 2003).

What to do.

• Ensure good drainage. Grow cucumber on raised beds, especially in regions with frequent rains. For heavy clay soils, ridges and beds are essential so that water does not stagnate in the root zone.
• Do not water unnecessarily. In cool or rainy weather, reduce or stop watering altogether. Cucumber does not like “wet feet”.
• Loosen soil after watering and rains. Loosening breaks the soil crust, improves gas exchange and helps roots “breathe”. Be careful near roots – do not damage them.
• Use covers during prolonged rains. Plastic tunnels or temporary canopies can protect plantings from waterlogging.

3.3. Uneven Watering

Symptoms. Fruits become curved, misshapen – hook‑shaped, with constrictions, thickened at one end. Fruit skin may crack. Ovary drop and bitterness are often observed (Mondal et al., 2020; Wien & Stützel, 2020).

Why it happens. Cucumber fruit grows very quickly – only 7–12 days pass from ovary to technical maturity (Wien & Stützel, 2020). Such rapid growth requires a steady flow of water and nutrients. When watering is uneven (e.g., once a week – sometimes a lot, sometimes little), the plant periodically experiences water stress. During dry periods, fruit growth slows, and after watering it resumes. As a result, different parts of the fruit grow at different rates, and it becomes deformed. Moreover, uneven watering enhances the accumulation of cucurbitacin, causing bitterness (Mondal et al., 2020).

What to do.

• Water regularly, maintaining stable soil moisture. It is better to water every 2–3 days with the same amount of water than once a week with overwatering.
• Use drip irrigation. Drip irrigation provides uniform and metered water supply directly to the root zone, eliminating moisture fluctuations. This is especially effective in greenhouses and small plots.
• When hand‑watering, use the same amount each time. Water until the root zone is thoroughly wet, then pause until the soil begins to dry at a depth of 5–7 cm (but do not allow complete drying).
• Adjust watering according to growth stage. During flowering and active fruiting, moisture demand is highest. At the beginning of growth and during ripening (if you do not harvest greens continuously) – reduce.

How to Control Water Regime: Practical Guidelines

Important additions:

• Water should be warm – not below +20 °C. Cold water causes root shock and exacerbates all described disorders (Tarakanov & Mukhin, 2003).
• In hot weather, refreshing irrigation (sprinkling) is useful – spraying plants with water at midday. This lowers leaf temperature by 5–8 °C and increases air humidity (Tarakanov & Mukhin, 2003).
• Never water cucumber over the leaves in sunny weather – this causes burns. Water only at the root, or do sprinkling only in cloudy weather or morning/evening.

Key idea. A stable water regime is the foundation of cucumber health. Sharp fluctuations in moisture (from drought to waterlogging) are much more dangerous than a slight constant deficit. Develop a habit of regular, uniform watering – and you will avoid most problems with fruit, bitterness and yield.

4.1. Macronutrient Deficiencies

4.2. Micronutrient Deficiencies

4.3. Element Excess and Toxicity

Excess of elements is as dangerous as deficiency, and often even more so, as it causes specific toxic effects.

4.4. Element Imbalance (Antagonism)

Antagonism is when excess of one element interferes with the uptake of another. This is especially important for cucumber.

What to do. Apply fertilisers in a balanced manner, based on soil agrochemical analysis. Avoid one‑sided application of individual elements. In complex cases – use foliar sprays with chelated forms, which are better absorbed and interact less with other elements in the soil.

Deficiency and Excess Symptoms: Quick‑Reference Table

Main Principles for Nutritional Disorders:

1. First check soil pH. Optimal pH for cucumber is 6.0–6.8. Deviations towards acidic or alkaline make many elements unavailable, and fertilisation becomes useless.

2. Consider growth stage. Early in the season, cucumber consumes more phosphorus (for roots); during flowering and fruiting – potassium and calcium. Nitrogen is needed throughout the season, but during fruiting its excess can cause vegetative overgrowth (vigorous vines but few fruits).

3. Foliar feeding is the fastest route. When micronutrient deficiency is suspected or when roots are impaired (cold soil, waterlogging), foliar feeding gives results within 2‑3 days.

4. Do not try to compensate for one element's deficiency with excess of another. This worsens imbalance. Use balanced complex fertilisers for cucumber or apply elements individually, strictly following dosages.

5. Soil and leaf analysis is the best diagnostic tool. If you regularly face nutritional problems, conduct agrochemical analysis of soil or plant tissue. This will save you money, time and nerves.

Remember: most element deficiencies in cucumber are not so much a lack of the elements themselves in the soil, but their unavailability due to incorrect pH, cold soil or uneven watering. Therefore, correcting watering regime and maintaining pH is 80% of solving nutritional problems.

5.1. Empty Flowers (Predominance of Male Flowers)

Symptoms. Many yellow flowers on the plant that do not form ovaries – they sit on long thin pedicels, gathered in clusters of 5‑7. Female flowers (with a characteristic thickening‑ovary at the base) are either absent or very few. The plant blooms abundantly, but there are no fruits (Mondal et al., 2020; Tarakanov & Mukhin, 2003).

Why it happens. In cucumber, flower sex is not genetically fixed but depends on environmental conditions at the time of flower bud initiation. Male flowers are the “default” option. Female flowers form only under certain conditions that signal the plant of well‑being and sufficient resources for fruiting. Predominance of male flowers is a protective response: under stress, the plant conserves resources, not spending them on fruit formation, but ensuring maximum pollen dispersal (Wien & Stützel, 2020).

Main causes of empty flowers:

What to do.

• Normalise temperature. If hot – shade and humidify air (refreshing irrigation). If cold – cover plants.
• Optimise watering. Soil should be steadily moist, but not waterlogged.
• Balance nutrition. Reduce the share of nitrogen fertilisers (especially ammonium forms), increase phosphorus and potassium. Apply monopotassium phosphate (10–15 g/m²) or a complex fertiliser high in phosphorus and potassium.
• Pinch the main stem. For many varieties, pinching the growing point stimulates lateral shoot growth, which bear more female flowers. This is especially effective for bee‑pollinated and some parthenocarpic varieties.
• Use growth regulators. Gibberellin‑based preparations can suppress male flowers and stimulate female flower formation, but their use requires precise dosage and is generally not recommended for amateur gardening.

5.2. Ovary Drop

Symptoms. Young ovaries (small cucumbers 1‑3 cm long) turn yellow, then dry and drop. Sometimes unopened buds also drop. With mass ovary drop, yield drops sharply (Mondal et al., 2020; Wehner et al., 2020).

Why it happens. The ovary is an actively growing organ that requires a constant supply of water, nutrients, and most importantly – assimilates (photosynthesis products). If the plant cannot supply all ovaries with resources, it drops the “extra” ones. This is a normal self‑regulation mechanism, but under stress it becomes excessive (Wien & Stützel, 2020).

Main causes of ovary drop:

What to do.

• Ensure good pollination. For bee‑pollinated varieties, attract insects (plant nectar‑bearing plants nearby, do not use insecticides during flowering). Hand pollination can be done – transfer pollen from male to female flower with a soft brush.
• Stabilise watering. Soil should be moist but not waterlogged. Water regularly, especially during mass flowering and fruiting.
• Feed with potassium and phosphorus fertilisers. Potassium is critical for ovary retention. Monopotassium phosphate (10–15 g/m²) is an excellent option.
• Do not allow overloading. If there are too many ovaries (especially in parthenocarpic hybrids), remove some of the weakest so that the rest receive enough nutrition. This is especially important under low light.
• Control temperature. On hot days, shade and humidify air. On cold nights, cover plants.
• Use foliar boron and molybdenum sprays. These elements improve pollination and fertilisation. Spraying with boric acid (0.1%) and ammonium molybdate (0.05%) during flowering gives a good effect.

5.3. Complete Absence of Ovaries

Symptoms. Plants flower, but ovaries do not form at all – even small ovaries are absent. This is a more serious problem than ovary drop, as it indicates a systemic failure in the reproductive system.

Why it happens.

• Using the wrong varieties. If you planted a bee‑pollinated variety and there is no insect access in a greenhouse, ovaries will not form. Or vice versa: a parthenocarpic hybrid is pollinated by insects – in some such varieties, pollination produces deformed fruits and ovaries may drop.
• Critical heat. At daytime temperatures above +35 °C, pollen becomes completely sterile, and in parthenocarpic varieties, hormonal signals for ovary growth are disrupted (Wehner et al., 2020).
• Extreme stress. The combination of high temperature, low humidity and water shortage blocks all reproductive processes. The plant switches to survival mode and does not produce fruits.
• Genetic features. Some old varieties or improperly selected hybrids may have a genetic predisposition to poor fruiting.

What to do. First – check conditions: temperature, humidity, watering. Eliminate stress factors. If the cause is pollination – ensure insect access or hand pollinate. If weather is critically hot and the variety is parthenocarpic, try using ovary‑stimulating preparations (e.g., based on gibberellin or auxin), but strictly according to instructions. Next season, choose varieties that match your conditions: for greenhouses – parthenocarpic, for open ground – bee‑pollinated or self‑pollinating.

5.4. Fruit Deformation (General Causes)

We will discuss specific fruit deformations in Chapter 6, but here we note general causes related to flowering and fruiting disorders.

Why fruits become deformed. Cucumber fruit grows very quickly – 7‑12 days from ovary to harvest maturity. Any disruption of conditions during this period causes different parts of the fruit to grow unevenly. Deformation is based on uneven distribution of assimilates and water among fruit cells, as well as uneven pollination (for bee‑pollinated varieties). If one of the three stigmatic lobes receives insufficient pollen, seeds in that sector do not develop, and the fruit grows crookedly (Mondal et al., 2020; Wehner et al., 2020).

Main causes of deformation related to flowering and fruiting:

• Insufficient pollination (for bee‑pollinated varieties) → curvature, narrowing in the middle.
• Temperature fluctuations → fruits with constrictions, hook‑shaped (see Chapter 6).
• Uneven watering → fruits thickened at one end.
• Potassium deficiency → pear‑shaped fruits (thickening at stalk).
• Boron deficiency → fruits with corky spots, cracking.

5.5. Uneven Fruit Growth

This is when fruits on the same plant differ significantly in size, shape and growth rate, and also when a fruit grows in spurts – sometimes fast, sometimes stopping.

Why it happens. Cucumber is a plant with strong competition between fruits for assimilates. The first ovaries formed become dominant and take the main share of photosynthetic products. Younger ovaries formed later receive less nutrition, so they grow slower. If the load on the plant is too high, it may drop weak ovaries or sharply slow their growth (Wien & Stützel, 2020).

In addition, uneven growth can be caused by:

• unstable watering (moisture fluctuations);
• nutritional deficiency (especially potassium);
• low night temperatures (growth slows at night, accelerates during the day);
• plant ageing (declining photosynthesis at end of season).

What to do. To even out fruiting:

• Maintain stable conditions (watering, temperature, nutrition).
• Remove the first 2‑3 ovaries at early stages to stimulate uniform development of subsequent fruits.
• Harvest greens regularly – this stimulates new ovary formation.
• Feed plants during mass fruiting with potassium and phosphorus, carry out foliar feeding with complex fertilisers.

Summary of Flowering and Fruiting

Key thought: All flowering and fruiting problems are the plant's response to instability. Cucumber demands predictable conditions: stable warmth, constant moisture, even nutrition. If you provide this, the plant will reward you with a bountiful harvest of straight, beautiful fruits.

6.1. Fruit Bitterness

Symptoms. Fruits have an unpleasant bitter taste, noticeable even in small amounts. Bitterness may be uniform throughout the fruit or more pronounced near the stalk and in the skin. In some varieties, bitterness appears only during certain periods and disappears when conditions improve (Mondal et al., 2020; Wehner et al., 2020).

Physiological mechanism. Bitterness is caused by cucurbitacins – a group of tetracyclic triterpenoid compounds that protect the plant from herbivores. These substances are synthesised in all parts of the cucumber, but their concentration in fruits is usually low. Under stress (drought, heat, temperature fluctuations, nutrient deficiency), cucurbitacin biosynthesis is activated and they accumulate in fruits. Old varieties are especially sensitive to this – modern hybrids often carry genes that suppress cucurbitacin accumulation even under stress (Wehner et al., 2020; Wien & Stützel, 2020).

Main causes of bitterness accumulation:

• Lack of soil moisture – the most common cause. Under drought, cucurbitacin synthesis sharply increases.
• High temperature (> 30 °C) combined with low air humidity.
• Sharp temperature fluctuations (more than 10 °C between day and night).
• Nutritional deficiency (especially potassium and phosphorus), which weakens the plant.
• Uneven watering – alternating drought and waterlogging.
• Stress from transplanting or mechanical root damage.

What to do.

• Ensure regular and even watering. Soil in the root zone should be consistently moist, without water stagnation. Use mulch to retain moisture.
• Maintain optimal temperature. In heat – shade and humidify air. In cold – cover.
• Choose varieties and hybrids with genetic resistance to bitterness. Modern parthenocarpic hybrids (e.g., those with Bt‑ or bi‑ markers in some types) practically do not accumulate bitterness even under stress (Wehner et al., 2020). For open ground, choose hybrids resistant to stress conditions.
• Harvest fruits promptly. Overgrown fruits are more likely to be bitter – pick greens regularly, not allowing overgrowth.
• If bitterness appears, adjust watering and potassium fertilisation. Potassium application (potassium sulfate 10‑15 g/m²) can reduce cucurbitacin accumulation.

Important: bitterness is not a sign of toxicity, but it significantly reduces fruit quality. Peeling and removing the stalk can partially reduce bitterness, as the main concentration of cucurbitacin is in these parts (Mondal et al., 2020).

6.2. Fruit Curvature (Crooked Fruit)

Symptoms. Fruit is bent in an arc, “pretzel”‑shaped, or has a noticeable bend in the middle. Curvature is often accompanied by uneven thickness: one side may be more developed than the other (Mondal et al., 2020; Wehner et al., 2020).

Physiological mechanism. Curvature arises from uneven cell growth in different parts of the fruit. The main causes of this inequality are uneven pollination (for bee‑pollinated varieties) and unstable environmental conditions. During pollination, pollen lands on one or two of the three stigmatic lobes. In the part of the ovary where fertilisation occurred, seeds begin to develop actively, releasing growth hormones (auxins, gibberellins) that stimulate growth of surrounding tissues. In unpollinated sectors, growth slows or stops – resulting in a curved fruit. Under stress (temperature fluctuations, uneven watering), this effect is amplified because assimilate transport to the fruit is disrupted (Wien & Stützel, 2020).

What to do.

• Ensure full pollination. For bee‑pollinated varieties, attract insects, hand‑pollinate, especially in greenhouses.
• Stabilise conditions. Avoid sharp temperature and humidity fluctuations during flowering and fruit growth.
• Use parthenocarpic hybrids. They do not require pollination and produce more uniform fruits, because ovary growth is stimulated by its own hormones, not by fertilisation (Wehner et al., 2020).
• Maintain optimal plant density. Dense planting worsens lighting and intensifies competition for assimilates among fruits.

6.3. Hook‑Shaped Fruit

Symptoms. Fruit has a characteristic hook‑shaped bend – a strong curvature at the apex (distal end), often with thickening or narrowing at the bend. The hook may point upward or downward (Mondal et al., 2020; Tarakanov & Mukhin, 2003).

Physiological mechanism. Hook‑shape is a particular case of curvature, but with a more pronounced bend in the most active growth zone – the distal (flower) end. This deformation occurs during sharp fluctuations between day and night temperatures (difference more than 10 °C) during fruit growth. On cold nights, cell division in the fruit tip slows; on warm days, it accelerates. As a result, the tip “runs ahead” while the rest of the fruit lags in growth, creating the characteristic hook. Hook‑shape can also be caused by potassium deficiency or insufficient pollination (Mondal et al., 2020; Wehner et al., 2020).

What to do.

• Smooth out temperature fluctuations. In greenhouses, use heat accumulators (water containers), cover material at night. In open ground – covers and timely ventilation.
• Provide plants with potassium. Apply potassium sulfate or potassium magnesium sulfate (10‑15 g/m²). Potassium improves assimilate transport to fruits and their uniform growth.
• Monitor pollination. For bee‑pollinated varieties – hand pollination or attract insects.
• Remove hook‑shaped fruits. They consume resources but do not give quality yield. Better to remove them so the plant directs energy to new, properly formed ovaries.

6.4. Thickening at the Stalk (Bottleneck Fruit)

Symptoms. Fruit is thickened at the stalk end (“bottleneck” shape), and narrows towards the apex. The tip may be pointed or even hook‑shaped. Often the seed cavity is underdeveloped in the distal part (Mondal et al., 2020; Wehner et al., 2020).

Physiological mechanism. Thickening at the stalk is caused by uneven distribution of assimilates within the fruit. Normally, assimilates (sugars, amino acids) enter the fruit through vascular bundles and are distributed evenly. Under stress (especially potassium shortage), assimilate transport to the distal (flower) part is disrupted. The part near the stalk receives enough nutrition, while the tip suffers from starvation. As a result, cells in the stalk part grow and divide actively, while those in the apical part grow slowly. This deformation is intensified by insufficient pollination (especially in bee‑pollinated varieties), when seed development in the distal part is weaker (Mondal et al., 2020; Wien & Stützel, 2020).

What to do.

• Provide sufficient potassium nutrition. Potassium is the main element improving carbohydrate transport to fruits. Apply potassium fertilisers (potassium sulfate, potassium magnesium sulfate) during active fruiting.
• Balance watering. Do not allow soil drying during fruit growth.
• Carry out foliar potassium feeding (0.5‑1% potassium sulfate or monopotassium phosphate solution) to quickly correct deficiency.
• Remove severely deformed fruits – they will not recover, and resources will be wasted.

6.5. Thickening at the Apex (Pear‑Shaped Fruit)

Symptoms. Fruit thickened at the distal (flower) end, and narrowed at the stalk. Shape resembles an inverted pear. Often accompanied by rough skin and thickened pericarp in the thickened part (Mondal et al., 2020; Wehner et al., 2020).

Physiological mechanism. This deformation is the opposite of the previous one and is caused by insufficient pollination in the stalk part of the ovary, as well as potassium deficiency against a background of nitrogen excess. With excess nitrogen, the plant spends much energy on vegetative growth, and fruits suffer from lack of assimilates. The apical part, being a more active growth zone, “draws” nutrition to itself, while the base remains underdeveloped. In bee‑pollinated varieties, pear‑shape often occurs if pollen only landed on the distal part of the stigma (Mondal et al., 2020).

What to do.

• Balance the nitrogen‑potassium ratio. Reduce nitrogen fertiliser share, increase potassium. The N:K ratio during fruiting should be about 1:1.5‑2.
• Ensure full pollination. For bee‑pollinated – hand pollination or attract insects.
• Apply foliar potassium feeding (monopotassium phosphate 10‑15 g/10 L water).
• Harvest greens regularly – overgrown fruits are more often deformed.

6.6. Fruit Growth Arrest

Symptoms. Ovaries have formed but do not grow or grow very slowly. Fruits remain small, often yellow and drop. Leaves may look healthy (Mondal et al., 2020; Wehner et al., 2020).

Physiological mechanism. Fruit growth is an energy‑intensive process requiring a constant supply of assimilates. If the plant experiences stress (cold, drought, fruit overload), it may temporarily or completely stop ovary growth to conserve resources for survival. The main cause is photosynthesis deficit (too little light, damaged leaves) or disrupted assimilate transport (low night temperatures, potassium deficiency). During cold nights (< +16 °C), fruit cells stop dividing and growth halts until warming, but if cold persists – fruits “freeze” and do not recover (Wien & Stützel, 2020).

What to do.

• Provide comfortable night temperature. Not below +16 °C. Use covers during cold periods.
• Maintain stable watering and nutrition. Potassium nutrition is especially important to improve assimilate transport.
• Do not overload the plant. If there are too many ovaries – remove some weak ones so the rest receive enough resources.
• Ensure adequate light for the plant. If dense, thin plantings, remove excess leaves shading the ovaries.
• Check root system. Cold, waterlogged or compacted soil impairs root function – then foliar feeding is faster and more effective.

6.7. Fruit Cracking

Symptoms. Longitudinal or transverse cracks appear on fruit skin, which may be deep (to flesh) or superficial. Cracks often appear at the base or along the entire length (Mondal et al., 2020; Tarakanov & Mukhin, 2003).

Physiological mechanism. Cracking is a consequence of sharp changes in fruit growth rate. Usually this occurs due to uneven watering: after a long drought, abundant watering causes fruit cells to actively absorb water and rapidly increase in size. The skin (exocarp) cannot keep up with the growth of internal tissues and tears, forming cracks. Cracking can also be caused by calcium or boron deficiency – these elements are involved in building strong cell walls. When deficient, cell walls become brittle, and even slight tension causes ruptures (Mondal et al., 2020; Wehner et al., 2020).

What to do.

• Stabilise watering. Avoid sharp transitions from drought to waterlogging. Water regularly, maintaining stable soil moisture.
• Use mulch to smooth moisture fluctuations.
• Apply calcium and boron. Calcium – for cell wall strength (calcium nitrate, 0.5% foliar). Boron – for strengthening cell walls and improving calcium transport (boric acid 0.1% foliar, 1‑2 times).
• Do not allow fruit overripening. Overripe fruits are more prone to cracking.
• Harvest greens on time, do not leave them on the plant longer than required.

6.8. Fruit Yellowing

Symptoms. Fruits turn yellow (light yellow or lemon‑yellow) before reaching consumer ripeness. Fruits may remain small, sometimes with signs of wilting or softening (Mondal et al., 2020; Wehner et al., 2020).

Physiological mechanism. Fruit yellowing is premature senescence induced by stress or hormonal imbalance. Usually occurs with:

• Nitrogen deficiency – the plant mobilises nitrogen from fruits to young leaves, causing yellowing.
• High temperature (> 35 °C) – chlorophyll breaks down, fruits lose green colour.
• Potassium deficiency – assimilate transport disrupted, fruits do not receive nutrition and begin to senesce.
• Overload with fruits – the plant sheds “ballast”, directing resources to remaining fruits.
• Ethylene exposure (when stored with apples, bananas, tomatoes) – ethylene accelerates ripening and senescence, causing yellowing even on the plant (Mondal et al., 2020; Wehner et al., 2020).

What to do.

• Balance nutrition. Ensure plants receive adequate nitrogen (but not excess), potassium and phosphorus.
• Control load. Do not leave too many fruits on the plant at once – remove some excess ovaries.
• Avoid overheating. On hot days, shade and humidify air.
• Avoid storing cucumbers together with ethylene‑releasing fruits (apples, bananas, tomatoes), especially at harvest collection points (Mondal et al., 2020).
• Harvest fruits regularly, not letting them overripen on the plant.

Summary Table of Fruit Defects

Main Conclusion on Fruit Defects

All fruit deformities and defects are not accidental, but a diagnostic signal. The plant tells you: “Something is wrong with watering, temperature or nutrition.” Pay close attention to the shape and colour of greens – this is the fastest way to notice problems and correct conditions before losing yield. If you see recurring defects, analyse your agronomic background and adjust care – and in the next fruiting wave you will get healthy, even fruits.

7.1. Variety Selection – The First Step in Prevention

Modern breeding has created cucumber hybrids resistant to specific stress factors: heat, cold, moisture deficit, as well as bitterness and major diseases (Wehner et al., 2020). Choosing the right variety is the foundation on which all prevention is built.

What to look for when choosing:

• For open ground in regions with cold nights – choose cold‑tolerant hybrids with genetic resistance to low temperatures (e.g., marked “cold‑tolerant”, “for northern regions”).
• For hot regions – heat‑tolerant hybrids that retain ovaries even at +32…+35 °C.
• For greenhouses – parthenocarpic hybrids (not requiring pollination), they produce uniform fruits without curvature and do not suffer from lack of insects.
• For bitterness protection – look for hybrids labelled “bitter‑free” (genetically unable to accumulate cucurbitacin). This is especially important for regions with hot, dry summers (Wehner et al., 2020).

Why it works: Genetic resistance is a “safety margin” that allows the plant to withstand stresses without serious developmental disorders. It does not replace good care, but makes it more effective.

7.2. Stable Watering – The Basis of Healthy Fruiting

Cucumber is a “water” plant, and most of its problems are related to water regime. The main principle of prevention is evenness and regularity, not the amount of water.

Rules for stable watering:

Additional tip: in hot climates, refreshing irrigation (sprinkling) at midday is effective – it cools leaves and increases air humidity. Water consumption – 50‑80 L/m², but this does not replace root watering, only complements it (Tarakanov & Mukhin, 2003).

7.3. Balanced Nutrition – Prevention of Deformities

Cucumber nutrition should be balanced according to growth stages. You cannot use the same fertilisation scheme throughout the season. The plant has different requirements for nutrients depending on the stage of development (Mondal et al., 2020; Tarakanov & Mukhin, 2003).

Nutrition plan by growth stage:

Important rules:

• Do not overfeed nitrogen during fruiting – this causes “vegetative overgrowth” (vigorous vines but few fruits) and provokes deformations (pear‑shape).
• Potassium and calcium are the main elements for fruit quality. Their deficiency is the primary cause of curvature, cracking and bitterness.
• Foliar feeding (on leaves) is the fastest way to deliver elements to the plant, especially when roots are impaired (cold soil, waterlogging, root damage). Use it as “first aid”, but do not completely replace root nutrition.

7.4. Temperature Control – Protection from Stress

The temperature regime for cucumber should be stable, without sharp jumps. Prevention of temperature stress is daily attention to weather forecasts and prompt reaction.

What to do in heat:

• Shade plants during midday with shading net (30‑50% shade) or white non‑woven material.
• Humidify air by sprinkling during the hottest hours.
• Ensure good ventilation in greenhouses.
• Water more often (but do not increase single rate) to maintain soil moisture.

What to do in cold:

• Use cover material at night (spunbond, lutrasil) – it adds 2‑4 °C.
• In greenhouses, use water containers as heat accumulators: water warms during the day, releases heat at night.
• Grow on raised beds and use dark mulch to warm soil.
• Water only with warm water.

What to do during sharp fluctuations:

• Smooth fluctuations by avoiding sudden greenhouse ventilation.
• In open ground, temporary covers help mitigate night cooling.
• Foliar potassium and calcium fertilisation increases plant resistance to temperature fluctuations.

7.5. Timely Harvest and Proper Plant Training

These two practices are often underestimated, although they directly affect the physiological state of plants and fruit quality.

Why timely harvest is important:

• Overgrown fruits (even a 1‑2 day delay) become powerful “competitors” for young ovaries. They draw assimilates to themselves, delaying growth of new fruits.
• Left on the plant, overgrown fruits stimulate plant senescence and shorten the fruiting period.
• Regular harvest (every 1‑2 days) stimulates new ovary formation and ensures even yield (Wien & Stützel, 2020).

Proper plant training:

• Removing lower leaves and shoots improves ventilation and lighting, reduces fungal disease risk and improves fruit quality.
• Pinching the main stem in bee‑pollinated varieties stimulates lateral shoot growth, which produce more female flowers.
• Thinning ovaries – if there are too many ovaries on the plant (especially in parthenocarpic hybrids), remove some of the weakest so that the rest receive enough nutrition. This prevents growth arrest and mass drop.
• Removing old leaves, especially yellowed and damaged ones – they do not photosynthesise, are a source of infection and consume resources.

7.6. Controlling Yield Load

Cucumber is a very productive crop, but it cannot always “feed” all ovaries, especially under low light or nutrition. Overloading leads to ovary drop, growth arrest, deformation and yellowing of fruits (Wien & Stützel, 2020).

Signs of overload:

• Many small ovaries that do not grow for a long time.
• Fruits become small, deformed, with uneven colour.
• Lower leaves yellow and die faster than usual.
• Plant looks “tired” – few new shoots, weak growth.

What to do for load regulation:

• Harvest greens regularly (this stimulates new ovary formation).
• Remove some weak, small or curved ovaries.
• During mass fruiting, feed with potassium and phosphorus – they improve assimilate transport and allow the plant to withstand high load.
• Under low light (cloudy weather, dense planting) – reduce the number of ovaries left, as photosynthesis is limited.

7.7. Monitoring and Early Diagnosis

Prevention of physiological disorders is impossible without regular observation of plants. The earlier you notice a problem, the easier and faster it is to correct.

What to check daily:

• Leaf condition (colour, turgor, deformations).
• Size and colour of ovaries (any yellowing, growth arrest).
• Fruit shape (appearance of curvature, hook‑shape).
• Soil moisture at a depth of 5‑10 cm.
• Air and soil temperature (especially in greenhouse).

Keep a simple observation diary: note watering dates, fertilisations, weather anomalies and plant responses. This will help you identify patterns and adjust care in future seasons.

Comprehensive Prevention – A System

All the measures listed above are not separate “life‑hacks” but interconnected elements of one system. Ignoring at least one of them reduces the effectiveness of all the others.

Main principle: do not wait until plants “cry out” for help – create stable, comfortable conditions from the start. Then they will spend energy not on fighting stress, but on growth and fruiting. And the harvest will certainly please you!

Mistake 1. Looking for Infection Where There Is None

Seeing yellowed leaves, wilting or spots on fruits, many immediately recall fungal and bacterial diseases and rush to treat plantings with fungicides. This is one of the most frequent and most harmful mistakes.

Why it is a mistake. Physiological disorders, unlike infectious diseases, have no pathogen and do not spread from plant to plant. Applying fungicides in such a situation is a waste of money and time, and most importantly – additional stress for the weakened plant. Many fungicides are phytotoxic, especially in heat, and can cause leaf burns (Akhatov et al., 2013). Moreover, uncontrolled chemical use destroys beneficial rhizosphere microflora and promotes pathogen resistance where it really exists.

How to do it correctly. When any symptoms appear, first assess the conditions: soil and air temperature, soil moisture, watering regime, fertilisation schedule and composition. If the problem is widespread and uniform across the plot – it is highly likely a physiological stress. If symptoms are focal and spread gradually – then conduct diagnostics for pathogens. And only after excluding physiological factors, start chemical protection (Mondal et al., 2020).

Mistake 2. Uncontrolled Preventive Use of Pesticides

Some gardeners spray cucumbers with fungicides and insecticides “just in case”, believing it will strengthen plants. This is a deep misconception.

Why it is a mistake. Preventive use of pesticides without real threat is a waste of resources and creation of additional stress load. Chemicals disrupt the waxy coating on leaves, suppress respiration and photosynthesis, and also kill beneficial pollinating insects and natural enemies of pests (Wehner et al., 2020). Moreover, systemic fungicides and insecticides can accumulate in fruits, which is dangerous for consumers.

How to do it correctly. Use pesticides only when a real threat is detected (appearance of pests or pathogens in quantities exceeding the economic threshold). In other cases, rely on agronomic prevention methods: crop rotation, removal of plant residues, maintaining a healthy microclimate and balanced nutrition. These are the foundation of disease protection (Akhatov et al., 2013; Tarakanov & Mukhin, 2003).

Mistake 3. Trying to Compensate Problems with Excessive Fertilisation

Noticing that the plant is growing poorly or fruits are deformed, the gardener often decides: “I need to fertilise!” – and applies increased doses of fertilisers, often all at once or with a nitrogen bias.

Why it is a mistake. Excess fertiliser is no less dangerous than deficiency. Excessive nitrogen causes “vegetative overgrowth” – vigorous dark‑green vines but weak flowering and fruit set. Excess potassium blocks calcium and magnesium uptake, provoking blossom‑end rot and interveinal chlorosis. Overfeeding with phosphorus can cause zinc and iron deficiency (Mondal et al., 2020; Wehner et al., 2020). In addition, high salt concentration in soil (salinisation) disrupts osmotic pressure, and roots stop absorbing water – the plant wilts even in moist soil.

How to do it correctly. Before applying fertilisers, diagnose: assess plant appearance, determine which element is lacking (by symptom localisation), and only then apply a balanced dose of that specific element. It is better to under‑fertilise than to over‑fertilise. Apply fertilisers in fractions, according to growth stages, and always follow label instructions (Tarakanov & Mukhin, 2003).

Mistake 4. Ignoring Temperature and Watering Regime

Focusing on fertilisation, gardeners often overlook the two main factors determining cucumber health: temperature and humidity. Yet, it is water and temperature regime disturbances that are the root of most problems.

Why it is a mistake. Cucumber is a tropical crop, and its physiological processes (cell division, photosynthesis, assimilate transport, pollination) work normally only within a narrow temperature range and with stable humidity. If soil temperature drops below +16 °C, roots stop absorbing phosphorus and potassium – and even the most generous fertilisation becomes useless. If watering is insufficient in heat, fruits become bitter and curved (Wien & Stützel, 2020; Mondal et al., 2020).

How to do it correctly. For any problem, first check soil temperature (at 10‑15 cm depth) and soil moisture (visually or using simple methods – squeeze a lump). If they are outside cucumber's comfort range, all other measures will be of little effect. Restoring normal hydro‑thermal conditions is 80% of success in combating physiological disorders (Tarakanov & Mukhin, 2003).

Mistake 5. Diagnosing Based on a Single Symptom

Many beginning gardeners try to diagnose based on a single symptom, ignoring other signs and conditions. For example, seeing interveinal chlorosis, they immediately claim iron deficiency, although it could be magnesium, manganese deficiency or even potassium excess.

Why it is a mistake. Different disorders can give similar external manifestations. For instance, interveinal chlorosis on young leaves can be caused by iron, manganese, zinc deficiency or even calcium excess. Localisation of symptoms (on old or young leaves) and accompanying conditions (soil pH, weather, watering) are decisive for correct diagnosis (Mondal et al., 2020; Wehner et al., 2020).

How to do it correctly. Analyse the combination of signs:

• Where do symptoms appear – on old or young leaves?
• What is the form of symptoms – interveinal chlorosis, marginal scorch, necrosis, deformation?
• What conditions preceded the symptoms (cold snap, heat, drought, heavy watering)?
• What is the soil pH (critical for availability of many elements)?

Only by comparing all these factors can you make the correct “diagnosis” and choose the right course of action.

Mistake 6. Applying Aggressive Measures Without Analysing Conditions

For example, when plants wilt (often caused by cold soil or waterlogging), the gardener starts treating plants with stimulants, pruning leaves, or even transplanting them.

Why it is a mistake. Wilting under cold soil or waterlogging is a result of root dysfunction, not disease. Leaf pruning in such a situation only increases stress, and transplanting injures roots further. Stimulants may give a temporary effect but do not eliminate the cause (Akhatov et al., 2013; Wien & Stützel, 2020).

How to do it correctly. Before taking any action, determine the root cause. Check soil temperature: if below +16 °C – warm it (covers, mulch, warm‑water irrigation). Check moisture: if waterlogged – stop watering, ensure drainage, loosen soil. Only after eliminating the cause apply supportive measures – foliar feeding, stimulants.

Mistake 7. Using Cold Water for Watering in Hot Weather

On hot days, gardeners often rush to water cucumbers with cold water from a well or borehole, thinking it will refresh the plants. In fact, this is one of the most dangerous mistakes.

Why it is a mistake. The sharp temperature contrast between cold water (often +10…+12 °C) and sun‑heated soil causes root shock. Root vessels contract, and the plant cannot absorb water despite its abundance in the soil. This leads to so‑called “physiological wilting” – the plant looks dried out although the soil is wet. In addition, cold water promotes root rot (Pythium, Fusarium) and blocks phosphorus uptake (Tarakanov & Mukhin, 2003; Wien & Stützel, 2020).

How to do it correctly. Always use warm water (+20…+25 °C) for watering cucumbers. To do this, place barrels or other containers on site where water will heat in the sun. In cool weather, water can be additionally warmed. Water only at the root, avoiding leaves.

Mistake 8. Ignoring Varietal Characteristics

Growing parthenocarpic hybrids in open ground where insects are present, or conversely, bee‑pollinated varieties in a greenhouse without pollinators – a common mistake.

Why it is a mistake. Parthenocarpic hybrids do not need pollination, but when pollinated by insects, they often develop ugly, curved fruits with rough skin and large seeds. Bee‑pollinated varieties planted in a greenhouse without insect access either do not set fruit at all or produce very few ovaries (Wehner et al., 2020; Wien & Stützel, 2020).

How to do it correctly. Clearly distinguish the purpose of varieties:

• For greenhouses and polytunnels choose parthenocarpic hybrids – they do not require pollination and produce even, beautiful fruits.
• For open ground – bee‑pollinated or self‑pollinating varieties, while ensuring insect access to flowers (do not use insecticides during flowering, plant nectar‑bearing plants nearby).
• In regions with unstable weather or absence of insects – give preference to parthenocarpic varieties even for open ground; they are more reliable.

Final Conclusion

Physiological disorders of cucumber are not a verdict, but a signal that growing conditions need adjustment. To successfully cope with them, it is important to avoid typical mistakes:

1. Do not look for disease where there is none. First check conditions – temperature, watering, nutrition.

2. Do not overuse pesticides. They do not cure physiological disorders, only add stress.

3. Feed plants in a balanced way, according to growth stage needs, not “by eye”.

4. Remember the main thing: watering and temperature are the foundation of cucumber health. Fertilisation is only a supplement.

5. Diagnose comprehensively, not by a single symptom.

6. Do not act aggressively without analysis – first find the cause, then correct it.

7. Use only warm water for watering.

8. Choose varieties that match your growing conditions.

And most importantly: observe your plants daily. The earlier you notice deviations, the easier and faster you can correct them. Cucumber is a very responsive crop, and with proper care it will surely reward you with a bountiful and high‑quality harvest.