Physiological disorders

Differences from Infectious Diseases

The main difference between physiological disorders and diseases caused by pathogens (fungi, bacteria, viruses) is the absence of an infectious agent. They are not contagious.

Practical takeaway: If you notice symptoms on one plant while neighboring ones look healthy, it could be the start of an infection. If the problem is widespread and linked to weather conditions or your agronomic practices, it is most likely a physiological disorder.

Main Causes

All physiological disorders arise because the plant is experiencing stress. Essentially, it is its "cry for help." The main groups of causes include:

1. Water regime disturbances: both drought and waterlogging.

2. Nutritional imbalances: an imbalance of macro- and microelements (Agustí, 2010). This can be a deficiency or an excess of a particular element (Milošević and Milošević, 2020).

3. Adverse weather conditions: frost, sharp temperature fluctuations, sunburn, hail (Trunov and Samoshchenkov, 2012).

4. Environmental factors: air pollution, soil salinity (Milošević and Milošević, 2020).

Reversibility of Changes

It is crucial to understand that the consequences of physiological disorders can be reversible, partially reversible, or irreversible.

1. Reversible: These are disorders that can be fixed by eliminating the cause. For example, leaves yellowed from nitrogen deficiency will regain their color after fertilization. Fruits damaged by drought can plump up after timely watering. Young shoots affected by spring frosts can produce new growth.

2. Partially reversible: Tissue damage may not fully recover, but the plant can heal wounds and continue to develop normally. For instance, frost cracks on the trunk can be cleaned and treated, after which the tree can survive. Sunburn on the bark can also heal over time. However, the appearance of these areas will remain altered.

3. Irreversible: These are cases where damage leads to the death of entire organs or the whole plant. For example, the death of fruit buds during severe winter frosts means there will be no harvest that year. The death of bark in a complete ring around the trunk will inevitably lead to the tree's death (Trunov and Samoshchenkov, 2012).

Key Diagnostic Principle

To distinguish a physiological disorder from a disease:

1. Rule out pathogens: inspect leaves and branches with a magnifying glass for spores, webs, insects, or their larvae.

2. Recall the weather: has there been severe drought, torrential rain, sharp cold snaps, or extreme heat recently?

3. Analyze your care: did you apply fertilizers on time? What was the last watering like? Was there any herbicide drift from a neighboring field?

4. Assess the scale: is the problem localized (on one branch) or widespread (on all trees)?

The answers to these questions will guide you towards the right path to saving your harvest.

This was a draft of the first chapter. How do you find this approach and style? We can move on to the next chapter: 2. Water-Related Disorders.

2.1. Drought (Water Deficit)

Symptoms:

Lack of water is one of the most severe stressors for plums. You may notice the following signs:

• Leaves: lose turgor, become limp, droop; the edges of the leaf blade may curl upward and turn yellow (chlorosis). In severe drought, leaves may fall prematurely (Westwood, 1993).
• Shoots: stop growing. Annual growth becomes short and thin.
• Fruits: become smaller, less juicy, and may drop before reaching maturity. Taste deteriorates: sugar content decreases, acidity increases.
• Overall tree: weakens, winter hardiness and disease resistance decrease.

Cause:

Lack of available moisture in the soil. This can be caused by:

• Prolonged absence of rain.
• High temperatures increasing evaporation.
• Improper (insufficient) irrigation regime.
• Excessive weed growth competing for moisture.

What to do and why it works:

1. Ensure regular watering. During active growth and fruit filling (late spring to summer), the soil in the root zone (down to 50-70 cm) should be moist (Krivko, 2014).

• For young orchards: watering during dry periods is particularly critical as the root system is not yet developed. Water into the tree pits, aiming to wet the soil to a depth of 40-50 cm (Krivko, 2014).
• For bearing orchards: the optimal method is drip irrigation, which delivers water directly to the root zone. If unavailable, use furrow or basin irrigation. The irrigation rate depends on soil type and tree age but averages 30-50 liters per square meter of the tree circle.
• Why it works: water is necessary for dissolving and transporting nutrients, maintaining cell turgor, cooling leaves, and most importantly, for photosynthesis, which provides the tree with energy for growth and fruit development.

2. Mulching. Covering the tree circle with a layer (about 10 cm) of organic material (compost, mown grass, straw, manure) significantly reduces moisture evaporation from the soil. Mulch also prevents weed growth and root overheating.

3. Keep the soil loose. Unlike bare fallow, which severely dries out the soil, it is better to use systems with grassed inter-rows, regularly mowing the grass to reduce evaporation (Krivko, 2014). However, during dry periods, it is recommended to keep the tree rows as black fallow to conserve moisture, avoiding cultivation which breaks capillaries and increases evaporation.

2.2. Waterlogging (Water Stress)

Symptoms:

Excess water is as harmful as its deficit. Problems arise because water displaces air from the soil, causing roots to suffer from oxygen starvation (asphyxia).

• Leaves: become pale green or yellow (chlorosis), especially on young leaves. With prolonged waterlogging, leaves may fall prematurely.
• Shoots: growth is suppressed.
• Roots: rot, especially the absorbing rootlets. Cracks and gum exudate may appear on the trunk bark.
• Fruits: become watery, lose sugar content, and often crack.

Cause:

• Prolonged heavy rains.
• Frequent and excessive watering, especially on heavy clay soils.
• High water table.
• Poor site drainage.

What to do and why it works:

1. Provide drainage. This is the main condition for growing plums on heavy, waterlogged soils. Plums prefer well-drained loamy soils (Agustí, 2010; Trunov and Samoshchenkov, 2012).

• Why it works: roots need oxygen for respiration. It is virtually absent in water. Good drainage allows excess water to drain away, leaving air pores in the soil essential for normal root function.

2. Choose the right location. Do not plant plums in lowlands where cold air and water stagnate, nor on sites with a high water table (closer than 1.5-2 m) (Trunov and Samoshchenkov, 2012).

3. Adjust watering. During rainy periods, watering should be completely stopped. With drip irrigation, adjust the regime according to the weather. To check soil moisture, use the "hand feel" method—squeeze a handful of soil from a 15-20 cm depth. If it easily crumbles, watering is needed.

2.3. Water Balance Disruption: Fruit Cracking

Symptoms:

This is perhaps the most noticeable and unpleasant water-related disorder. Deep cracks appear on the fruit, making them unsuitable for storage and often for consumption (Westwood, 1993). Cracks can be radial (from the stem end) or transverse. Pathogens often enter through these cracks, leading to rapid spoilage (Agustí, 2010).

Cause:

Cracking occurs due to a sudden shift in water balance. Fruits adapted to dry conditions have thick, less elastic skins. When heavy rain or intense irrigation follows a prolonged drought, the tree actively sends water to the fruits. The flesh (mesocarp) swells rapidly, increasing in volume, while the skin (exocarp), having lost elasticity, cannot withstand the pressure and bursts.

What to do and why it works:

1. Regular watering. The main preventive measure is to maintain stable soil moisture throughout the fruit growth period. Avoid sharp transitions from "dry" to "wet." Watering should be regular and moderate (Westwood, 1993). A plum that has not experienced severe thirst will not react so violently to rain.

• Why it works: the fruit skin will constantly be in a state of "readiness" and will be elastic enough to withstand water intake.

2. Mulching and loosening. As mentioned, these practices help smooth out fluctuations in soil moisture.

Important: This disorder is a classic example of how stress (drought) triggers a physiological response (cracking), which is often mistaken for a disease. Remember, the culprit here is not a fungus but an unstable water regime.

3.1. Nutrient Deficiencies

Nutrient deficiency symptoms vary depending on the element's mobility within the plant. Mobile elements (N, P, K, Mg) can move from old leaves to young ones, so their deficiency first appears on older, lower leaves. Immobile elements (Ca, Fe, Zn, B, Mn) cannot do this, and their deficiency shows on young, terminal leaves (Srivastava et al., 2020).

3.2. Nutrient Excesses

Excess nutrients are as dangerous as deficiencies. They can cause toxicity, block the uptake of other elements, and lead to serious physiological disorders.

• Excess Nitrogen (N): Causes "luxuriant" growth — excessive shoot growth that does not mature properly and overwinters poorly. The tree becomes more susceptible to diseases. Fruits store poorly, their taste deteriorates, and the skin may become coarse. Plum flavor becomes less pronounced (Agustí, 2010). Excess nitrogen also promotes dense canopy growth, reducing light and air circulation.
• Excess Potassium (K): Blocks the uptake of magnesium and calcium, causing their deficiency despite their presence in the soil. Symptoms include marginal scorch and chlorosis linked to Mg and Ca shortages.
• Excess Boron (B): The threshold between deficiency and toxicity for boron is very narrow. Excess causes necrosis of leaf margins and tips, and dieback. Can lead to bud and fruit death.
• Excess Chlorine (Cl): Plum is very sensitive to chlorine. Using potassium fertilizers containing chlorine (potassium chloride) can cause chlorosis and marginal leaf scorch. Therefore, it is recommended to use chlorine-free potassium forms (Agustí, 2010; Milošević and Milošević, 2020).

What to do in case of excess:

1. Stop applying the corresponding fertilizer.

2. Heavy watering on light soils can help leach excess salts from the root zone.

3. Applying organic matter helps bind excess ions into less available forms.

4. To reduce boron toxicity, liming of acidic soils can be done.

3.3. Nutrient Imbalance (Antagonism and Synergism)

This is the most subtle and complex issue. Often, an element deficiency occurs not from its absence in the soil, but from impaired uptake due to interactions with other elements. This phenomenon is called antagonism.

Examples of antagonism:

• Potassium ⇄ Magnesium ⇄ Calcium: Excess of one of these elements blocks the uptake of the other two. For example, excessive potassium application can cause magnesium chlorosis, even if enough magnesium is in the soil (Milošević and Milošević, 2020).
• Potassium ⇄ Sodium: In saline soils, excess sodium hinders potassium uptake.
• Phosphorus ⇄ Zinc: Excess phosphorus in the soil often causes zinc deficiency (zinc deficiency, "rosetting") (Milošević and Milošević, 2020).
• Nitrogen ⇄ Potassium: Excessive nitrogen nutrition increases the need for potassium.

What to do:

1. Rely on soil and leaf analysis. This is the only accurate way to know what is happening in your orchard. Levels of macro- and micronutrients in soil and leaves (in midsummer, 120 days after flowering) are objective indicators (Agustí, 2010; Milošević and Milošević, 2020).

2. Apply fertilizers in a balanced manner, considering the ratios between elements. For example, a good K:Mg:Ca balance is approximately 3:1:2.

3. Use complex fertilizers that contain all necessary elements in a balanced form.

4. Regularly check soil pH and maintain it in the optimal range (5.5-6.5 for plums), as pH strongly affects the availability of all elements (Milošević and Milošević, 2020).

Practical takeaway: An element deficiency does not always mean "add it." First, find out why it occurred: perhaps due to incorrect pH, excess of another element, or root system problems. Treatment should start by addressing these root causes.

4.1. Frost Damage

Frost is the most dangerous abiotic factor for plums, especially in regions with harsh winters and late spring frosts. Damage can range from death of flower buds to cracking of the trunk bark.

Symptoms and types of frost damage:

1. Damage to flower buds: This is the most common cause of crop failure. Buds turn brown, blacken, become loose and dry when cut. In spring, they do not open or produce deformed flowers. Buds are particularly vulnerable after thaws when they break dormancy (Westwood, 1993; Trunov and Samoshchenkov, 2012).

2. Frost cracks (bark splits): Vertical tears in the bark and wood on the trunk and scaffold branches. Most often appear on the south and southwest sides of the tree due to sharp day-night temperature fluctuations ("winter sunscald") (Westwood, 1993). The crack area can rot over time, weakening and killing the tree.

3. Freezing of bark and cambium: On the trunk and branches, bark peels, darkens, and becomes loose. The cambium (green layer under the bark), when cut, has a brown color instead of green.

4. Root damage: Less visible but very dangerous. Plum roots are less winter-hardy than the above-ground parts. Root damage manifests as weak spring growth, leaf chlorosis, and delayed bud break.

Cause:

• Winter frosts: Tissue damage occurs when water inside cells freezes, forming ice crystals that rupture cell walls (Westwood, 1993). Frosts after prolonged thaws are especially dangerous, as plants lose their acclimation to cold.
• Spring frosts: Late frosts during flowering are the main enemy of the plum harvest. Plum flowers are damaged at temperatures of -2...-4°C, and fruit set can die at -1...-2°C (Agustí, 2010; Trunov and Samoshchenkov, 2012).

What to do and why it works:

1. Proper variety and site selection. Choose regionalized varieties suited to your climate zone. For northern regions, varieties with late flowering are preferred to avoid spring frosts (Trunov and Samoshchenkov, 2012). Avoid planting in lowlands ("cold pockets") where cold air accumulates.

• Why it works: Late-flowering varieties pass the critical stage when frost probability is already lower.

2. Protection against spring frosts:

• Smudging: Lighting smoky fires when the temperature drops to 0°C creates a smoke screen that reduces heat radiation from the soil (Westwood, 1993; Krivko, 2014).
• Sprinkling: Using fine mist sprinklers during frost. Freezing water releases heat that protects flowers from damage (Westwood, 1993).
• Covering: Young trees or low-growing varieties can be covered with agrotextile, paper, or cloth overnight.

3. Post-frost care:

• Pruning damaged branches: In spring, remove all dry, blackened, and frost-damaged branches back to healthy wood. This prevents disease development.
• Treating wounds: Frost cracks and other bark wounds should be cleaned to healthy tissue, disinfected (with copper sulfate solution), and covered with grafting wax.

4. Winter preparation: Autumn water-charging irrigation (November) significantly increases tree winter hardiness. Moist soil freezes slower and protects roots (Krivko, 2014).

• Why it works: Water has high heat capacity; it accumulates heat and protects the root system from sharp temperature fluctuations.

4.2. Heat and Sunburn Damage

Symptoms:

• Leaf scorch: Leaves (especially young ones) become pale, with dry, discolored areas, often between veins or at margins. Leaves curl and drop.
• Fruit sunburn: On fruits, especially the south-facing side, pale, then browning, depressed spots appear. The flesh under the spot becomes dry, hard, and loses taste. Affected fruits often crack and rot.
• Bark sunburn (winter sunscald): As mentioned, in late winter to early spring, when the sun starts to warm but nights are still cold, the bark on the south side of the trunk heats up and then rapidly cools. This causes cambium tissue death; the bark cracks and peels (Westwood, 1993; Trunov and Samoshchenkov, 2012).

Cause:

• High temperature + low humidity: This combination leads to strong evaporation from leaves and fruit surfaces, which roots cannot compensate for.
• Sharp temperature fluctuations: Particularly dangerous for bark.

What to do and why it works:

1. Regular watering in heat: During dry periods, water plums, especially when temperatures exceed 30°C. This prevents overheating and dehydration.

• Why it works: Water evaporating from leaf surfaces cools the plant, protecting it from overheating.

2. Whitewashing trunks and scaffold branches: In autumn or late winter, whitewash trunks and large branch bases (Trunov and Samoshchenkov, 2012). This is one of the most effective ways to protect against winter sunscald. Whitewash reflects sunlight, preventing bark overheating.

• Why it works: White reflects up to 90% of solar rays, keeping the bark cool. Use lime (2 kg per bucket of water) with added copper sulfate and glue for better adherence.

3. Fruit protection: In southern regions, shade nets can be used to prevent fruit sunburn, or avoid removing excess foliage on the south side of the canopy.

4.3. Air Pollution

Symptoms:

Industrial emissions (especially sulfur dioxide, fluoride compounds, ozone) can cause leaf necrosis and chlorosis in plums. Often, this appears as small yellowish or brown spots between veins, which expand over time. Leaf margins may curl and dry.

Cause:

Toxic gases enter leaves through stomata and cause tissue death. Plum is quite sensitive to air pollution (Westwood, 1993).

What to do:

• Primarily, this is about proper site selection. It is not recommended to establish orchards near large industrial facilities or high-traffic highways.
• Regular watering and balanced fertilization (especially potassium and calcium) increase plant resistance to toxicants.
• Why it works: A well-developed, healthy plant has a stronger antioxidant system and copes better with oxidative stress caused by pollutants.

4.4. Salt Stress (Soil Salinization)

Symptoms:

Externally, salt stress resembles drought: leaves wilt, margins and tips dry, turning brown ("marginal scorch"). Tree growth is suppressed; leaves may yellow and drop. In severe salinization, a whitish salt crust appears on the soil surface.

Cause:

Excess soluble salts (especially sodium, chlorine, and sulfates) in the soil solution. This can be caused by:

• Irrigation with water of high mineralization (above 1-2 g/L).
• Excessive application of mineral fertilizers.
• High saline groundwater table.
• Salt accumulation in arid regions due to insufficient rainfall (Milošević and Milošević, 2020; Krivko, 2014).

High salt concentration prevents roots from absorbing water (osmotic shock) and causes toxicity. Plum is particularly sensitive to salinity (Agustí, 2010).

What to do and why it works:

1. Water and soil analysis: Before establishing an orchard, check water quality and soil salinity levels. Plums grow poorly when irrigation water total mineralization exceeds 1.5-2 g/L (Krivko, 2014).

2. Leaching irrigation: If soil is saline, apply abundant watering (water-charging) to wash salts into deeper layers, beyond the root zone (Krivko, 2014).

• Why it works: Excess water dissolves salts and carries them downward, cleaning the upper, root-occupied layer.
• Apply organic fertilizers: Organic matter improves soil structure, increases water-holding capacity and buffering, partially reducing salt toxicity.
• Use gypsum application: On solonetzic soils (with excess sodium), gypsum application is effective, replacing sodium ions with less harmful calcium (Milošević and Milošević, 2020).
• Choose the right rootstock: On saline soils, prefer varieties and rootstocks with higher salt tolerance (e.g., certain myrobalan plum forms).

5.1. Flower and Fruit Drop (Physiological Fruit Drop)

Symptoms:

Massive shedding of flowers (usually right after flowering) or young fruit set (about pea-sized, the so-called "June drop"). This is normal if the tree only drops weak, deformed, or excess fruitlets. But if shedding is massive and threatens the harvest, it is a disorder.

Causes:

1. Nutrient and water deficiency: After flowering, the tree expends huge nutrient reserves on fruit set growth. If reserves are insufficient, it sheds "extra" fruits it cannot "feed" (Agustí, 2010). This is especially common with nitrogen, potassium, phosphorus, or soil moisture shortages after flowering (Westwood, 1993).

2. Poor pollination: If flowers were poorly pollinated (cold, rainy, or windy weather during flowering, lack of bees), few seeds develop. Fruits with few seeds produce less hormones that keep them attached, and they drop (Trunov and Samoshchenkov, 2012).

3. Crop overload: In a year of abundant flowering, the tree attempts to set more fruits than it can support. This is a natural self-regulation mechanism, but if the variety is prone to overload, drop can be excessive.

4. Frost: Damage to flowers or set by spring frosts causes them to blacken and drop (Westwood, 1993; Trunov and Samoshchenkov, 2012).

5. Stress: Sharp temperature changes, drought, waterlogging—all increase drop.

Distinction from pests:

• Codling moth or sawfly bore holes inside the fruitlets, leaving pinholes and signs of feeding (frass). Dropped fruits often have damage.
• Physiological drop occurs with undamaged flowers and fruitlets, without signs of pests.

What to do and why it works:

1. Ensure adequate nutrition and watering: During flowering and immediately after (1-2 weeks), apply nitrogen and potassium (e.g., a complex fertilizer with NPK) and provide regular watering (if no rain) (Agustí, 2010; Krivko, 2014).

• Why it works: The tree receives "building materials" for fruit set growth and reduces stress from resource shortage.

2. Improve pollination: To attract bees, spray trees with sugar water (1 tablespoon sugar per liter of water) or plant nectar-bearing plants nearby. During weak flowering, keep bees in the orchard throughout the bloom. During abundant flowering, the first 2-3 days are enough to limit excessive fruit set (Trunov and Samoshchenkov, 2012).

3. Crop thinning: If the tree is overloaded with flowers, perform manual thinning of fruitlets when they reach the size of a hazelnut. Leave a distance of 5–8 cm between fruits (depending on variety). This reduces competition for nutrients and lowers the risk of massive drop (Agustí, 2010).

• Why it works: Remaining fruits receive more nutrition, grow better, and cause less stress to the tree.

4. Frost protection: See the previous chapter (smudging, sprinkling, covering).

Important: Some fruit drop (up to 20-30%) is normal for plum. If more than half drops, it is a signal for action. During abundant flowering, only 5-10% of flowers set fruit; the rest are shed (Agustí, 2010).

5.2. Fruit Cracking

Symptoms:

Longitudinal or transverse cracks appear on fruits, often deep. They make fruits unsuitable for storage and often attract pathogens (gray mold).

Causes:

• Sharp moisture fluctuations: After prolonged drought—heavy rain or intense irrigation. Fruits adapted to dry conditions have thick skins. When water rushes in, the flesh swells rapidly, and the skin bursts (Westwood, 1993).
• Calcium deficiency: This element strengthens cell walls. Its deficiency makes skins weaker (Milošević and Milošević, 2020).
• Genetic predisposition: Some plum varieties are more prone to cracking than others (e.g., those with thin skins and juicy flesh).

What to do and why it works:

1. Regular watering: Maintain stable soil moisture during fruit growth. It is better to water more frequently in smaller amounts than rarely and heavily. Use drip irrigation or furrow watering.

• Why it works: Stable moisture prevents sudden pressure changes inside the fruit.

2. Mulching: Mulch helps retain moisture and smooths out fluctuations.

3. Foliar calcium sprays: During fruit growth (2-3 weeks before expected harvest), spray trees with calcium nitrate or calcium chloride solution (0.5-1%) (Milošević and Milošević, 2020).

• Why it works: Calcium enters fruits directly and strengthens their skin.

5.3. Fruit Shrinkage (Small Fruits)

Symptoms:

Fruits grow small, not reaching the variety's typical size, even with a normal number of set fruits.

Causes:

1. Crop overload: The tree cannot "feed" all the set fruits, leaving them all small. This is a classic problem without thinning.

2. Nutrient and water deficiency: Especially during active fruit growth (the "filling" phase). Nitrogen, potassium, and water shortages severely limit fruit growth (Agustí, 2010).

3. Dense canopy: Poor light penetration to the canopy interior results in small, pale fruits.

4. Tree aging: Older trees have reduced productivity and fruits shrink even under good care.

What to do and why it works:

1. Crop thinning: The most effective method—remove some fruitlets manually or with chemical thinners (e.g., NAA, Sevin) from flowering to pit hardening (Agustí, 2010). Remaining fruits get more nutrients and grow larger.

• Why it works: Reducing the number of "competitors" for resources lets each remaining fruit receive more sugars, water, and minerals.

2. Abundant watering and fertilization: During active fruit growth (2-3 weeks after flowering), water and fertilize trees with complex fertilizers high in potassium.

3. Rejuvenation pruning: For old trees, perform rejuvenation pruning (removing old, bare branches) to stimulate new, more productive shoots.

5.4. Uneven Fruit Ripening

Symptoms:

Fruits on the same tree do not ripen simultaneously. Some have reached variety color and softness, while others remain green and firm. This complicates harvest and reduces marketability.

Causes:

1. Potassium deficiency: Potassium is responsible for sugar synthesis and transport, as well as fruit color. Its deficiency delays ripening (Agustí, 2010).

2. Lack of light: Fruits inside the canopy, in shade, ripen later than those in sunlight.

3. Dense canopy: Reduces both light and air circulation.

4. Crop overload: The tree distributes energy unevenly, and fruits on different branches may lack resources for simultaneous ripening.

5. Varietal characteristics: Some varieties (e.g., Hungarian) have more extended ripening than others (e.g., Reine Claude).

What to do and why it works:

1. Potassium fertilization: During fruit growth, apply potassium (potassium sulfate, potassium magnesium sulfate). This accelerates ripening and improves taste (Agustí, 2010).

• Why it works: Potassium activates enzymes responsible for sugar and anthocyanin (pigment) synthesis.

2. Canopy thinning: Remove overcrowded branches so sunlight reaches the entire canopy (Westwood, 1993). Especially important for tall varieties.

3. Selective harvesting: Pick fruits in 2-3 passes, starting with the largest and most colored ones.

5.5. Gummosis

Symptoms:

Drops or streaks of thick, sticky, amber or dark brown resin (gum) appear on the trunk, branches, and even fruits. Dried gum may look like glassy or matte growths (Agustí, 2010; Trunov and Samoshchenkov, 2012).

Causes:

Gum is the tree's defense reaction to damage. The resin "seals" the wound, preventing infection. However, gummosis itself is a symptom of stress. Main physiological causes:

1. Mechanical damage: Improper pruning (large stubs, bark tears), frost damage (frost cracks), sunburn, damage by rodents and insects (Westwood, 1993).

2. Waterlogging or drought: Sharp fluctuations in water balance cause internal tissue ruptures.

3. Excess nitrogen: Stimulates vigorous growth, making tissues loose and more vulnerable to damage and gummosis.

4. Scion-rootstock incompatibility: In rare cases, poor union of scion and rootstock tissues can cause gummosis at the graft union.

5. Fungal diseases (e.g., bacterial canker): Important to distinguish physiological gummosis from infectious. In bacterial canker, gum is often exuded from deep cankers with defined margins, and surrounding bark darkens and dies. In physiological cases, damage is usually superficial (mechanical) with no signs of active pathogen growth.

What to do and why it works:

1. Eliminate the cause: Stop gummosis by removing the source of stress:

• Adjust watering (do not overwater, but avoid drought).
• Stop nitrogen fertilization, especially in the second half of summer.

2. Treat wounds: Gum exudates must be removed by cleaning the wound to healthy wood (Westwood, 1993; Trunov and Samoshchenkov, 2012).

• Carefully scrape off gum and dead bark with a sharp knife.
• Wash the cleaned area with 1% copper sulfate solution (100 g per 10 L water) or 3% Bordeaux mixture.
• After drying, cover the wound with grafting wax, linseed oil-based paint, or a special paste (petrolatum + paraffin).
• Why it works: Grafting wax creates a barrier, preventing infection from entering the open wound and promoting healing.

Important: Gum is not a disease but a symptom. Treat not the gum but its cause. If gummosis is accompanied by deep cankers with dying bark, it is a sign of bacterial canker (Pseudomonas syringae), requiring more serious measures (removal of infected branches).

6.1. Optimal Agronomy

A healthy tree is one that receives everything it needs in the right amounts at the right time. Your task is to create this "baseline" environment.

6.2. Regular Tree Monitoring

An attentive gardener always spots problems early. Regular inspection is your main insurance against crop failure.

• Inspect trees: Conduct visual inspections at least 2-3 times a month, especially in spring and early summer.
• Pay attention to key indicators:
• Leaf color: any yellowing, paleness, chlorosis (interveinal or general), brown spots.
• Shoot condition: strong or weak growth, internode length.
• Bark appearance: any cracks, peeling, gummosis.
• Fruit development: normal size, shape, color; any spots, cracks, deformations.
• Record changes: Compare current state with previous observations. If leaves start to yellow or shoots slow down, it is a signal for action.
• Keep a garden diary: Record fertilization, watering, pruning, and weather conditions. This helps analyze the causes of disorders in the future.

6.3. Preventing Stress Factors

Stress is the main trigger for all physiological disorders. Your task is to mitigate its impact.

1. Avoid sharp changes: Do not apply large fertilizer doses at once; split them. Do not allow prolonged drought followed by heavy watering—this leads to fruit cracking.

2. Create a buffer zone: Mulch and a proper watering regime smooth out soil temperature and moisture fluctuations.

3. Control weeds: Around the trunk, they create additional competition.

4. Ensure balanced nutrition: Neither starvation nor overfeeding. Imbalance is also stress.

5. Monitor root health: Root damage is a major stressor. Avoid deep cultivation (especially in tree circles) that damages absorbing rootlets (Krivko, 2014).

Example Annual Prevention Plan: